Multi-factor authentication

Authentication takes place when someone tries to log into a computer resource (such as a computer network, device, or application). The resource requires the user to supply the identity by which the user is known to the resource, along with evidence of the authenticity of the user's claim to that identity. Simple authentication requires only one such piece of evidence (factor), typically a password, or occasionally multiple pieces of evidence all of the same type, as with a credit card number and a card verification code (CVC). For additional security, the resource may require more than one factor—multi-factor authentication, or two-factor authentication in cases where exactly two types of evidence are to be supplied.{{cite web |title = Two-factor authentication: What you need to know (FAQ) – CNET |url = http://www.cnet.com/news/two-factor-authentication-what-you-need-to-know-faq |website = CNET|access-date = 2015-10-31}}

The use of multiple authentication factors to prove one's identity is based on the premise that an unauthorized actor is unlikely to be able to supply all of the factors required for access. If, in an authentication attempt, at least one of the components is missing or supplied incorrectly, the user's identity is not established with sufficient certainty and access to the asset (e.g., a building, or data) being protected by multi-factor authentication then remains blocked. The authentication factors of a multi-factor authentication scheme may include:{{Cite journal|last1=Jacomme|first1=Charlie|last2=Kremer|first2=Steve|date=February 1, 2021|title=An Extensive Formal Analysis of Multi-factor Authentication Protocols|url=https://dl.acm.org/doi/10.1145/3440712|journal=ACM Transactions on Privacy and Security|publisher=Association for Computing Machinery|location=New York City|language=en|volume=24|issue=2|pages=1–34|doi=10.1145/3440712|s2cid=231791299|issn=2471-2566}}

• Something the user has: Any physical object in the possession of the user, such as a security token (USB stick), a bank card, a key, a phone that can be reached at a certain number, etc.
• Something the user knows: Certain knowledge only known to the user, such as a password, PIN, PUK, etc.
• Something the user is: Some physical characteristic of the user (biometrics), such as a fingerprint, eye iris, voice, typing speed, pattern in key press intervals, etc.

An example of two-factor authentication is the withdrawing of money from an ATM; only the correct combination of a physically present bank card (something the user possesses) and a PIN (something the user knows) allows the transaction to be carried out. Two other examples are to supplement a user-controlled password with a one-time password (OTP) or code generated or received by an authenticator (e.g. a security token or smartphone) that only the user possesses.{{Cite web|last=kaitlin.boeckl@nist.gov|date=2016-06-28|title=Back to basics: Multi-factor authentication (MFA)|url=https://www.nist.gov/itl/applied-cybersecurity/tig/back-basics-multi-factor-authentication|access-date=2021-04-06|website=NIST|language=en|archive-date=2021-04-06|archive-url=https://web.archive.org/web/20210406235123/https://www.nist.gov/itl/applied-cybersecurity/tig/back-basics-multi-factor-authentication|url-status=dead}}

An authenticator app enables two-factor authentication in a different way, by showing a randomly generated and constantly refreshing code, rather than sending an SMS or using another method.{{cite magazine | last=Barrett | first=Brian | title=How to Secure Your Accounts With Better Two-Factor Authentication | magazine=Wired | url=https://www.wired.com/story/two-factor-authentication-apps-authy-google-authenticator/ | date=July 22, 2018|access-date=12 September 2020}} This code is a Time-based one-time password (a TOTP)), and the authenticator app contains the key material that allows the generation of these codes.

{{main|knowledge-based authentication}}

Knowledge factors ("something only the user knows") are a form of authentication. In this form, the user is required to prove knowledge of a secret in order to authenticate.

A password is a secret word or string of characters that is used for user authentication. This is the most commonly used mechanism of authentication. Many multi-factor authentication techniques rely on passwords as one factor of authentication. Variations include both longer ones formed from multiple words (a passphrase) and the shorter, purely numeric, PIN commonly used for ATM access. Traditionally, passwords are expected to be memorized, but can also be written down on a hidden paper or text file.

File:SecureID token new.JPG

Possession factors ("something only the user has") have been used for authentication for centuries, in the form of a key to a lock. The basic principle is that the key embodies a secret that is shared between the lock and the key, and the same principle underlies possession factor authentication in computer systems. A security token is an example of a possession factor.

Disconnected tokens have no connections to the client computer. They typically use a built-in screen to display the generated authentication data, which is manually typed in by the user. This type of token mostly uses a OTP that can only be used for that specific session.{{cite web |title=Configuring One-Time Passwords |url=https://www.sonicwall.com/support/knowledge-base/configuring-one-time-passwords/170505594681886/ |website=www.sonicwall.com |publisher=Sonic Wall |access-date=19 January 2022}}

File:Black YubiKey 06.jpg

Connected tokens are devices that are physically connected to the computer to be used. Those devices transmit data automatically.{{Cite book|title = Encyclopedia of Cryptography and Security, Volume 1|publisher=Springer Science & Business Media|location=Berlin, Germany|year = 2011|isbn = 9781441959058|page = 1305|editor-last =van Tilborg|editor-first = Henk C.A.|editor-last2 = Jajodia|editor-first2 = Sushil}} There are a number of different types, including USB tokens, smart cards and wireless tags. Increasingly, FIDO2 capable tokens, supported by the FIDO Alliance and the World Wide Web Consortium (W3C), have become popular with mainstream browser support beginning in 2015.

A software token (a.k.a. soft token) is a type of two-factor authentication security device that may be used to authorize the use of computer services. Software tokens are stored on a general-purpose electronic device such as a desktop computer, laptop, PDA, or mobile phone and can be duplicated. (Contrast hardware tokens, where the credentials are stored on a dedicated hardware device and therefore cannot be duplicated, absent physical invasion of the device). A soft token may not be a device the user interacts with. Typically an X.509v3 certificate is loaded onto the device and stored securely to serve this purpose.{{Citation needed | date = September 2023 | reason = The last two sentences are not elaborated by the linked software token article.}}

Multi-factor authentication can also be applied in physical security systems. These physical security systems are known and commonly referred to as access control. Multi-factor authentication is typically deployed in access control systems through the use, firstly, of a physical possession (such as a fob, keycard, or QR-code displayed on a device) which acts as the identification credential, and secondly, a validation of one's identity such as facial biometrics or retinal scan. This form of multi-factor authentication is commonly referred to as facial verification or facial authentication.

Inherent factors ("something the user is"), are factors associated with the user, and are usually biometric methods, including fingerprint, face,{{Cite journal |last1=Cao |first1=Liling |last2=Ge |first2=Wancheng |date=2015-03-10 |title=Analysis and improvement of a multi-factor biometric authentication scheme: Analysis and improvement of a MFBA scheme |url=https://onlinelibrary.wiley.com/doi/10.1002/sec.1010 |journal=Security and Communication Networks |language=en |volume=8 |issue=4 |pages=617–625 |doi=10.1002/sec.1010}} voice, or iris recognition. Behavioral biometrics such as keystroke dynamics can also be used.

Increasingly, a fourth factor is coming into play involving the physical location of the user. While hard wired to the corporate network, a user could be allowed to login using only a pin code. Whereas if the user was off the network or working remotely, a more secure MFA method such as entering a code from a soft token as well could be required. Adapting the type of MFA method and frequency to a users' location will enable you to avoid risks common to remote working.{{Cite web |title=11 Tips for Protecting Active Directory While Working from Home |url=https://www.darkreading.com/cyberattacks-data-breaches/11-tips-for-protecting-active-directory-while-working-from-home |access-date=2024-08-29 |website=www.darkreading.com |language=en}}

Systems for network admission control work in similar ways where the level of network access can be contingent on the specific network a device is connected to, such as Wi-Fi vs wired connectivity. This also allows a user to move between offices and dynamically receive {{Clarify | text = the same level of network access| date = October 2023 | reason = The previous sentence sets the expectation that the user would be granted different levels of access when using from different devices/network.}} in each.{{cn|date=May 2023}}

File:Aegis Authenticator 3.2 screenshot.png

Two-factor authentication over text message was developed as early as 1996, when AT&T described a system for authorizing transactions based on an exchange of codes over two-way pagers.{{Cite web |date=2013-05-23 |title=Does Kim Dotcom have original 'two-factor' login patent? |url=http://www.theguardian.com/technology/2013/may/23/kim-dotcom-authentication-patents |access-date=2022-11-02 |website=the Guardian |language=en}}{{cite patent |number=0745961 |title=

Transaction authorization and alert system |gdate=1996-12-04 |country=EP}}

Many multi-factor authentication vendors offer mobile phone-based authentication. Some methods include push-based authentication, QR code-based authentication, one-time password authentication (event-based and time-based), and SMS-based verification. SMS-based verification suffers from some security concerns. Phones can be cloned, apps can run on several phones and cell-phone maintenance personnel can read SMS texts. Not least, cell phones can be compromised in general, meaning the phone is no longer something only the user has.

The major drawback of authentication including something the user possesses is that the user must carry around the physical token (the USB stick, the bank card, the key or similar), practically at all times. Loss and theft are risks. Many organizations forbid carrying USB and electronic devices in or out of premises owing to malware and data theft risks, and most important machines do not have USB ports for the same reason. Physical tokens usually do not scale, typically requiring a new token for each new account and system. Procuring and subsequently replacing tokens of this kind involves costs. In addition, there are inherent conflicts and unavoidable trade-offs between usability and security.{{cite journal |first1=Ding|last1=Wang|first2=Debiao|last2=He|first3=Ping|last3=Wang|first4=Chao-Hsien|last4=Chu|url=http://eprint.iacr.org/2014/135.pdf |title=Anonymous Two-Factor Authentication in Distributed Systems: Certain Goals Are Beyond Attainment |journal=IEEE Transactions on Dependable and Secure Computing|publisher=Institute of Electrical and Electronics Engineers|location=Piscataway, New Jersey|date=2014|access-date=2018-03-23}}

Two-step authentication involving mobile phones and smartphones provides an alternative to dedicated physical devices. To authenticate, people can use their personal access codes to the device (i.e. something that only the individual user knows) plus a one-time-valid, dynamic passcode, typically consisting of 4 to 6 digits. The passcode can be sent to their mobile device by SMS or can be generated by a one-time passcode-generator app. In both cases, the advantage of using a mobile phone is that there is no need for an additional dedicated token, as users tend to carry their mobile devices around at all times.

Notwithstanding the popularity of SMS verification, security advocates have publicly criticized SMS verification,{{cite magazine |url=https://www.wired.com/2016/06/hey-stop-using-texts-two-factor-authentication/ |title=So Hey You Should Stop Using Texts For Two-factor Authentication |author=Andy Greenberg |date=2016-06-26 |access-date=2018-05-12 |magazine=Wired}} and in July 2016, a United States NIST draft guideline proposed deprecating it as a form of authentication.{{cite web|title= NIST is No Longer Recommending Two-Factor Authentication Using SMS|url= https://www.schneier.com/blog/archives/2016/08/nist_is_no_long.html|date= August 3, 2016|access-date= November 30, 2017|publisher= Schneier on Security}} A year later NIST reinstated SMS verification as a valid authentication channel in the finalized guideline.{{cite web|title= Rollback! The United States NIST no longer recommends "Deprecating SMS for 2FA"|url= https://blogs.sap.com/2017/07/06/rollback-the-united-states-nist-no-longer-recommends-deprecating-sms-for-2fa/|date= July 6, 2017|access-date= May 21, 2019}}

As early as 2011, Duo Security was offering push notifications for MFA via a mobile app.{{cite web|url= http://www.duosecurity.com/features|title= Duo Security - Features|website= Internet Archive|archive-url= https://web.archive.org/web/20110628231224/http://www.duosecurity.com/features|access-date= 28 Jun 2011|archive-date= 28 June 2011}} In 2016 and 2017 respectively, both Google and Apple started offering user two-step authentication with push notifications as an alternative method.

{{cite web|last1= Tung|first1= Liam|url= https://www.zdnet.com/article/google-prompt-you-can-now-just-tap-yes-or-no-on-ios-android-to-approve-gmail-sign-in/|title= Google prompt: You can now just tap 'yes' or 'no' on iOS, Android to approve Gmail sign-in|website= ZD Net|access-date= 11 September 2017}}{{cite news

|author=Chance Miller |title= Apple prompting iOS 10.3

|url= https://9to5mac.com/2017/02/25/two-factor-authentication-ios-10-3/

|website= 9to5 Mac|access-date= 11 September 2017|date= 2017-02-25

}}

Security of mobile-delivered security tokens fully depends on the mobile operator's operational security and can be easily breached by wiretapping or SIM cloning by national security agencies.{{cite web|url= https://www.bellingcat.com/news/2016/04/30/russia-telegram-hack/|title= How Russia Works on Intercepting Messaging Apps – bellingcat|date= 2016-04-30|website= bellingcat|language= en-US|access-date= 2016-04-30|archive-url= https://web.archive.org/web/20160430211219/https://www.bellingcat.com/news/2016/04/30/russia-telegram-hack/|archive-date= 2016-04-30|url-status= dead}}

Advantages:

• No additional tokens are necessary because it uses mobile devices that are (usually) carried all the time.
• As they are constantly changed, dynamically generated passcodes are safer to use than fixed (static) log-in information.
• Depending on the solution, passcodes that have been used are automatically replaced in order to ensure that a valid code is always available, transmission/reception problems do not, therefore, prevent logins.

Disadvantages:

• Users may still be susceptible to phishing attacks. An attacker can send a text message that links to a spoofed website that looks identical to the actual website. The attacker can then get the authentication code, user name and password.{{cite news |last1=Kan |first1=Michael |title=Google: Phishing Attacks That Can Beat Two-Factor Are on the Rise |url=https://www.pcmag.com/news/367026/google-phishing-attacks-that-can-beat-two-factor-are-on-the |access-date=9 September 2019 |work=PC Mag |date=7 March 2019}}
• A mobile phone is not always available—it can be lost, stolen, have a dead battery, or otherwise not work.
• Despite their growing popularity, some users may not even own a mobile device, and take umbrage at being required to own one as a condition of using some service on their home PC.
• Mobile phone reception is not always available—large areas, particularly outside of towns, lack coverage.
• SIM cloning gives hackers access to mobile phone connections. Social-engineering attacks against mobile-operator companies have resulted in the handing over of duplicate SIM cards to criminals.{{cite web|url=https://www.theregister.co.uk/2017/07/10/att_falls_for_hacker_tricks/|title=Two-factor FAIL: Chap gets pwned after 'AT&T falls for hacker tricks'|first=Shaun|last=Nichols|date=10 July 2017|website=The Register|access-date=2017-07-11}}
• Text messages to mobile phones using SMS are insecure and can be intercepted by IMSI-catchers. Thus third parties can steal and use the token.{{Cite book|arxiv=1002.3171 |doi=10.1109/ISCC.2008.4625610 |isbn=978-1-4244-2702-4 |chapter=SSMS - A secure SMS messaging protocol for the m-payment systems |title=2008 IEEE Symposium on Computers and Communications |year=2008 |last1=Toorani |first1=Mohsen |last2=Beheshti |first2=A. |pages=700–705 |s2cid=5066992 }}
• Account recovery typically bypasses mobile-phone two-factor authentication.{{Failed verification | date = October 2023 | reason = The article says account recovery typically bypasses ALL 2FA, not just mobile phone.}}
• Modern smartphones are used both for receiving email and SMS. So if the phone is lost or stolen and is not protected by a password or biometric, all accounts for which the email is the key can be hacked as the phone can receive the second factor.
• Mobile carriers may charge the user messaging fees.

The Payment Card Industry (PCI) Data Security Standard, requirement 8.3, requires the use of MFA for all remote network access that originates from outside the network to a Card Data Environment (CDE).{{cite web|url=https://www.pcisecuritystandards.org/document_library?document=pci_dss|title=Official PCI Security Standards Council Site – Verify PCI Compliance, Download Data Security and Credit Card Security Standards|website=www.pcisecuritystandards.org|access-date=2016-07-25}} Beginning with PCI-DSS version 3.2, the use of MFA is required for all administrative access to the CDE, even if the user is within a trusted network.

The second Payment Services Directive requires "strong customer authentication" on most electronic payments in the European Economic Area since September 14, 2019.{{Citation|title=Commission Delegated Regulation (EU) 2018/389 of 27 November 2017 supplementing Directive (EU) 2015/2366 of the European Parliament and of the Council with regard to regulatory technical standards for strong customer authentication and common and secure open standards of communication (Text with EEA relevance.)|date=2018-03-13|url=http://data.europa.eu/eli/reg_del/2018/389/oj/eng|issue=32018R0389|language=en|access-date=2021-04-06}}

In India, the Reserve Bank of India mandated two-factor authentication for all online transactions made using a debit or credit card using either a password or a one-time password sent over SMS. This requirement was removed in 2016 for transactions up to ₹2,000 after opting-in with the issuing bank.{{cite news |last1=Karnik |first1=Madhura |title=Finally, Indians can use credit cards online without painful OTPs—but only for purchases under Rs2,000 |url=https://qz.com/india/854701/rbi-eases-two-factor-authentication-finally-indians-can-use-credit-cards-online-without-painful-otps-but-only-for-under-rs2000 |access-date=10 December 2023 |work=Quartz |date=7 December 2016 |language=en}} Vendors such as Uber have been mandated by the bank to amend their payment processing systems in compliance with this two-factor authentication rollout.{{cite news |last1=Agarwal |first1=Surabhi |title=Payment firms applaud RBI's move to waive off two-factor authentication for small value transactions |url=https://economictimes.indiatimes.com/news/economy/policy/payment-firms-applaud-rbis-move-to-waive-off-two-factor-authentication-for-small-value-transactions/articleshow/55856755.cms?from=mdr |access-date=28 June 2020 |work=The Economic Times |date=7 December 2016}}{{cite news |last1=Nair |first1=Vishwanath |title=RBI eases two-factor authentication for online card transactions up to Rs2,000 |url=https://www.livemint.com/Industry/bJmdHvAuLVC5af1O0NCE0O/RBI-eases-rules-for-online-card-payments-up-to-Rs2000.html |access-date=28 June 2020 |work=Livemint |date=6 December 2016 |language=en}}{{Cite web|date=2014-11-30|title=Uber now complies with India's two-factor authentication requirement, calls it unnecessary and burdensome|url=https://venturebeat.com/2014/11/30/uber-now-complies-with-indias-two-factor-authentication-requirement-calls-it-unnecessary-and-burdensome/|access-date=2021-09-05|website=VentureBeat|language=en-US}}

Details for authentication for federal employees and contractors in the U.S. are defined in Homeland Security Presidential Directive 12 (HSPD-12).{{Cite web|url=https://www.dhs.gov/homeland-security-presidential-directive-12|archive-url=https://web.archive.org/web/20120916062033/http://hspd12.usda.gov/about.html|url-status=dead|title=Homeland Security Presidential Directive 12|date=August 1, 2008|archive-date=September 16, 2012|website=Department of Homeland Security}}

IT regulatory standards for access to federal government systems require the use of multi-factor authentication to access sensitive IT resources, for example when logging on to network devices to perform administrative tasks{{cite web|url=http://www.sans.org/critical-security-controls/control.php?id=10|title=SANS Institute, Critical Control 10: Secure Configurations for Network Devices such as Firewalls, Routers, and Switches|access-date=2013-02-11|archive-url=https://web.archive.org/web/20130128051636/http://www.sans.org/critical-security-controls/control.php?id=10|archive-date=2013-01-28|url-status=dead}} and when accessing any computer using a privileged login.{{cite web|url=https://www.sans.org/critical-security-controls/control.php?id=12|title=SANS Institute, Critical Control 12: Controlled Use of Administrative Privileges|access-date=2013-02-11|archive-url=https://web.archive.org/web/20130128051708/http://www.sans.org/critical-security-controls/control.php?id=12|archive-date=2013-01-28|url-status=dead}}

NIST Special Publication 800-63-3 discusses various forms of two-factor authentication and provides guidance on using them in business processes requiring different levels of assurance.{{cite web|url=https://pages.nist.gov/800-63-3/|title=Digital Identity Guidelines|date=June 22, 2017|work=NIST Special Publication 800-63-3|publisher=NIST|access-date=February 2, 2018}}

In 2005, the United States' Federal Financial Institutions Examination Council issued guidance for financial institutions recommending financial institutions conduct risk-based assessments, evaluate customer awareness programs, and develop security measures to reliably authenticate customers remotely accessing online financial services, officially recommending the use of authentication methods that depend on more than one factor (specifically, what a user knows, has, and is) to determine the user's identity.{{cite web | url=http://www.ffiec.gov/press/pr101205.htm | title=FFIEC Press Release | date=2005-10-12 | access-date=2011-05-13 }} In response to the publication, numerous authentication vendors began improperly promoting challenge-questions, secret images, and other knowledge-based methods as "multi-factor" authentication. Due to the resulting confusion and widespread adoption of such methods, on August 15, 2006, the FFIEC published supplemental guidelines{{emdash}}which state that by definition, a "true" multi-factor authentication system must use distinct instances of the three factors of authentication it had defined, and not just use multiple instances of a single factor.{{cite web | date = 2006-08-15 | title = Frequently Asked Questions on FFIEC Guidance on Authentication in an Internet Banking Environment | url = https://www.ffiec.gov/pdf/authentication_faq.pdf | publisher = FFIEC | archiveurl = https://web.archive.org/web/20121115102618/http://www.ffiec.gov/pdf/authentication_faq.pdf | archivedate = 2012-11-15 | url-status = live }}

According to proponents, multi-factor authentication could drastically reduce the incidence of online identity theft and other online fraud, because the victim's password would no longer be enough to give a thief permanent access to their information. However, many multi-factor authentication approaches remain vulnerable to phishing,{{cite news|url=http://voices.washingtonpost.com/securityfix/2006/07/citibank_phish_spoofs_2factor_1.html|archive-url=https://web.archive.org/web/20110703141728/http://voices.washingtonpost.com/securityfix/2006/07/citibank_phish_spoofs_2factor_1.html|url-status=dead|archive-date=July 3, 2011|title=Security Fix – Citibank Phish Spoofs 2-Factor Authentication|newspaper=Washington Post |date=July 10, 2006 |author=Brian Krebs |access-date=20 September 2016}} man-in-the-browser, and man-in-the-middle attacks.{{cite web|url=http://www.schneier.com/blog/archives/2005/03/the_failure_of.html|title=The Failure of Two-Factor Authentication |work=Schneier on Security |author=Bruce Schneier |date=March 2005 |access-date=20 September 2016}} Two-factor authentication in web applications are especially susceptible to phishing attacks, particularly in SMS and e-mails, and, as a response, many experts advise users not to share their verification codes with anyone,{{cite web|url=https://www.kaspersky.com/blog/dont-send-codes/22448/|title=Why you shouldn't ever send verification codes to anyone |work=Kaspersky |author=Alex Perekalin|date=May 2018 |access-date=17 October 2020}} and many web application providers will place an advisory in an e-mail or SMS containing a code.{{cite journal|title=Mind your SMSes: Mitigating Social Engineering in Second Factor Authentication|year = 2017|doi = 10.1016/j.cose.2016.09.009|last1 = Siadati|first1 = Hossein|last2 = Nguyen|first2 = Toan|last3 = Gupta|first3 = Payas|last4 = Jakobsson|first4 = Markus|last5 = Memon|first5 = Nasir|journal = Computers & Security|volume = 65|pages = 14–28| s2cid=10821943 |doi-access = free}}

{{vague|text=Multi-factor authentication may be ineffective{{Cite web|last=Shankland|first=Stephen|title=Two-factor authentication? Not as secure as you'd expect when logging into email or your bank|url=https://www.cnet.com/news/two-factor-authentication-isnt-as-secure-as-you-might-expect-world-password-day/|access-date=2020-09-27|website=CNET|language=en}} against modern threats, like ATM skimming, phishing, and malware.{{cite web

|url=https://www.schneier.com/blog/archives/2012/02/the_failure_of_2.html

|title=The Failure of Two-Factor Authentication – Schneier on Security

|work=schneier.com |date=6 February 2012

|access-date=23 October 2015}}|date=April 2025}}{{Update inline|date=April 2025|?=yes}}

In May 2017, O2 Telefónica, a German mobile service provider, confirmed that cybercriminals had exploited SS7 vulnerabilities to bypass SMS based two-step authentication to do unauthorized withdrawals from users' bank accounts. The criminals first infected the account holder's computers in an attempt to steal their bank account credentials and phone numbers. Then the attackers purchased access to a fake telecom provider and set up a redirect for the victim's phone number to a handset controlled by them. Finally, the attackers logged into victims' online bank accounts and requested for the money on the accounts to be withdrawn to accounts owned by the criminals. SMS passcodes were routed to phone numbers controlled by the attackers and the criminals transferred the money out.{{Cite news|url=http://thehackernews.com/2017/05/ss7-vulnerability-bank-hacking.html|title=Real-World SS7 Attack – Hackers Are Stealing Money From Bank Accounts|last=Khandelwal|first=Swati|work=The Hacker News|access-date=2017-05-05|language=en-US}}

An increasingly common approach to defeating MFA is to bombard the user with many requests to accept a log-in, until the user eventually succumbs to the volume of requests and accepts one.{{cite web |title=MFA Fatigue: Hackers' new favorite tactic in high-profile breaches |url=https://www.bleepingcomputer.com/news/security/mfa-fatigue-hackers-new-favorite-tactic-in-high-profile-breaches/ |website=BleepingComputer |access-date=2023-08-12 |language=en-us}} This is called a multi-factor authentication fatigue attack (also MFA fatigue attack or MFA bombing) makes use of social engineering.{{Cite web |title=MFA Fatigue: Hackers' new favorite tactic in high-profile breaches |url=https://www.bleepingcomputer.com/news/security/mfa-fatigue-hackers-new-favorite-tactic-in-high-profile-breaches/ |access-date=2023-01-26 |website=BleepingComputer |language=en-us}}{{Cite web |last=Burt |first=Jeff |title=Multi-factor authentication fatigue can blow open security |url=https://www.theregister.com/2022/11/03/mfa_fatigue_enterprise_threat/ |access-date=2023-01-26 |website=www.theregister.com |language=en}}{{Cite web |last=Constantin |first=Lucian |date=2022-09-22 |title=Multi-factor authentication fatigue attacks are on the rise: How to defend against them |url=https://www.csoonline.com/article/3674156/multi-factor-authentication-fatigue-attacks-are-on-the-rise-how-to-defend-against-them.html |access-date=2023-01-26 |website=CSO Online |language=en}} When MFA applications are configured to send push notifications to end users, an attacker can send a flood of login attempts in the hope that a user will click on accept at least once.

In 2022, Microsoft has deployed a mitigation against MFA fatigue attacks with their authenticator app.{{Cite web |last=Tung |first=Liam |title=Microsoft Authenticator gains feature to thwart spam attacks on MFA |url=https://www.zdnet.com/article/microsoft-authenticator-gains-feature-to-thwart-spam-attacks-on-mfa/ |access-date=2023-01-26 |website=ZDNET |language=en}}

In September 2022 Uber security was breached by a member of Lapsus$ using a multi-factor fatigue attack.{{Cite news |last=Whittaker |first=Zack |date=2022-09-19 |title=How do you stop another Uber hack? |url=https://techcrunch.com/2022/09/19/how-to-fix-another-uber-breach/ |access-date=2023-08-24 |work=TechCrunch}}{{Cite news |last=Hardcastle |first=Jessica Lyons |date=2022-09-19 |title=Uber explains how it was pwned this month, points finger at Lapsus$ gang |url=https://www.theregister.com/2022/09/19/uber_admits_breach/ |access-date=2023-08-24 |work=The Register}} On March 24, 2023, YouTuber Linus Sebastian declared on the Linus Tech Tips channel on the YouTube platform that he had suffered an Multi-factor authentication fatigue attack.{{Cite AV media |url=https://www.youtube.com/watch?v=yGXaAWbzl5A |title=My Channel Was Deleted Last Night |date=2023-03-24 |last=Linus Tech Tips |access-date=2025-02-15 |via=YouTube}} In early 2024, a small percentage of Apple consumers experienced a MFA fatigue attack that was caused by a hacker that bypassed the rate limit and Captcha on Apple’s “Forgot Password” page.

Many multi-factor authentication products require users to deploy client software to make multi-factor authentication systems work. Some vendors have created separate installation packages for network login, Web access credentials, and VPN connection credentials. For such products, there may be four or five different software packages to push down to the client PC in order to make use of the token or smart card. This translates to four or five packages on which version control has to be performed, and four or five packages to check for conflicts with business applications. If access can be operated using web pages, it is possible to limit the overheads outlined above to a single application. With other multi-factor authentication technology such as hardware token products, no software must be installed by end-users.{{Citation needed | date = October 2023}} Some studies have shown that poorly implemented MFA recovery procedures can introduce new vulnerabilities that attackers may exploit. {{Cite arXiv |last1=Amft |first1=S. |last2=Höltervennhoff |first2=S. |last3=Huaman |first3=N. |last4=Krause |first4=A. |last5=Simko |first5=L. |last6=Acar |first6=Y. |last7=Fahl |first7=S. |title="We've Disabled MFA for You": An evaluation of the security and usability of multi-factor authentication recovery deployments |year=2023 |class=cs.CR |eprint=2306.09708 }}

There are drawbacks to multi-factor authentication that are keeping many approaches from becoming widespread. Some users have difficulty keeping track of a hardware token or USB plug. Many users do not have the technical skills needed to install a client-side software certificate by themselves. Generally, multi-factor solutions require additional investment for implementation and costs for maintenance. Most hardware token-based systems are proprietary, and some vendors charge an annual fee per user. Deployment of hardware tokens is logistically challenging. Hardware tokens may get damaged or lost, and issuance of tokens in large industries such as banking or even within large enterprises needs to be managed. In addition to deployment costs, multi-factor authentication often carries significant additional support costs.{{Citation needed | date = October 2023}} A 2008 survey{{cite web

|url=http://www.cujournal.com/issues/12_15/-100094-1.html

|archive-url=https://web.archive.org/web/20110708212931/http://www.cujournal.com/issues/12_15/-100094-1.html

|url-status=dead

|archive-date=July 8, 2011

|title=Study Sheds New Light On Costs, Effects Of Multi-Factor|date=4 April 2008}} of over 120 U.S. credit unions by the Credit Union Journal reported on the support costs associated with two-factor authentication. In their report, {{Clarify | text = software certificates and software toolbar approaches| date = October 2023 | reason = These weren't explained before.}} were reported to have the highest support costs.

Research into deployments of multi-factor authentication schemes{{Cite web|date=2011 |author1=Libicki, Martin C. |author2=Balkovich, Edward |author3=Jackson, Brian A. |author4=Rudavsky, Rena |author5=Webb, Katharine |title=Influences on the Adoption of Multifactor Authentication |url=https://www.rand.org/pubs/technical_reports/TR937.html|language=en}} has shown that one of the elements that tend to impact the adoption of such systems is the line of business of the organization that deploys the multi-factor authentication system. Examples cited include the U.S. government, which employs an elaborate system of physical tokens (which themselves are backed by robust Public Key Infrastructure), as well as private banks, which tend to prefer multi-factor authentication schemes for their customers that involve more accessible, less expensive means of identity verification, such as an app installed onto a customer-owned smartphone. Despite the variations that exist among available systems that organizations may have to choose from, once a multi-factor authentication system is deployed within an organization, it tends to remain in place, as users invariably acclimate to the presence and use of the system and embrace it over time as a normalized element of their daily process of interaction with their relevant information system.

While the perception is that multi-factor authentication is within the realm of perfect security, Roger Grimes writes{{Cite web|last=|first=|date=|title=Hacking Multifactor Authentication {{!}} Wiley|url=https://www.wiley.com/en-us/Hacking+Multifactor+Authentication-p-9781119650805|access-date=2020-12-17|website=Wiley.com|language=en-bb}} that if not properly implemented and configured, multi-factor authentication can in fact be easily defeated.

In 2013, Kim Dotcom claimed to have invented two-factor authentication in a 2000 patent,{{Cite patent | country = US | number = 6078908 | title = Method for authorizing in data transmission systems | inventor = Schmitz, Kim }} and briefly threatened to sue all the major web services. However, the European Patent Office revoked his patent{{ Cite web | url = https://arstechnica.com/information-technology/2013/05/kim-dotcom-claims-he-invented-two-factor-authentication-but-he-wasnt-first/ | title = Kim Dotcom claims he invented two-factor authentication—but he wasn't first | access-date = 25 July 2019 | first = Jon | last = Brodkin | date = 23 May 2013 | website = Ars Technica | archive-url = https://web.archive.org/web/20190709090048/https://arstechnica.com/information-technology/2013/05/kim-dotcom-claims-he-invented-two-factor-authentication-but-he-wasnt-first/ | archive-date = 9 July 2019 | df = dmy-all }} in light of an earlier 1998 U.S. patent held by AT&T.{{ Cite patent | country = US | number = 5708422 | title = Transaction authorization and alert system | inventor = Blonder, et al. }}

• Authentication factors
• Electronic authentication
• Identity management
• Multi-party authorization
• Mutual authentication
• Out-of-band
• Reliance authentication
• Universal 2nd Factor
• Identity threat detection and response

{{reflist}}

{{refbegin}}

• {{cite web |last1=Brandom |first1=Russell |title=Two-factor authentication is a mess |work=The Verge |date=2017-07-10 |url=https://www.theverge.com/2017/7/10/15946642/two-factor-authentication-online-security-mess |access-date=2017-07-10 |df=mdy-all }}

{{refend}}

{{sisterlinks|m=Help:Two-factor authentication|mw=Help:Two-factor authentication|d=Q7878662|voy=no|s=no|n=no|species=no|wikt=2FA|c=Category:Authentication_methods|b=Basic Computer Security|q=no|v=IT Security/Access Control/Authentication and Authorization}}

• [https://www.twofactorauth.org/ TwoFactorAuth.org] - TwoFactorAuth.org - An in-depth online resource for (2FA) and all it entails
• [https://www.theregister.co.uk/2011/03/18/rsa_breach_leaks_securid_data/ Attackers breached the servers of RSA and stole information that could be used to compromise the security of two-factor authentication tokens used by 40 million employees (register.com, 18 Mar 2011)]
• [http://it.slashdot.org/article.pl?sid=05/10/19/2340245&tid=172&tid=95 Banks to Use Two-factor Authentication by End of 2006], (slashdot.org, 20 Oct 2005)
• [https://web.archive.org/web/20081011073929/http://www.vnunet.com/vnunet/news/2126966/microsoft-abandon-passwords Microsoft to abandon passwords], Microsoft preparing to dump passwords in favour of two-factor authentication in forthcoming versions of Windows (vnunet.com, 14 Mar 2005)

{{Computer security}}

{{Authority control}}

Category:Authentication methods

Category:Computer access control