Forge Web Credentials: SAML Tokens
An adversary may forge SAML tokens with any permissions claims and lifetimes if they possess a valid SAML token-signing certificate. The default lifetime of a SAML token is one hour, but the validity period can be specified in the
NotOnOrAfter value of the
conditions ... element in a token. This value can be changed using the
AccessTokenLifetime in a
LifetimeTokenPolicy. Forged SAML tokens enable adversaries to authenticate across services that use SAML 2.0 as an SSO (single sign-on) mechanism.
An adversary may utilize Private Keys to compromise an organization's token-signing certificate to create forged SAML tokens. If the adversary has sufficient permissions to establish a new federation trust with their own Active Directory Federation Services (AD FS) server, they may instead generate their own trusted token-signing certificate. This differs from Steal Application Access Token and other similar behaviors in that the tokens are new and forged by the adversary, rather than stolen or intercepted from legitimate users.
An adversary may gain administrative Azure AD privileges if a SAML token is forged which claims to represent a highly privileged account. This may lead to Use Alternate Authentication Material, which may bypass multi-factor and other authentication protection mechanisms.
|M1015||Active Directory Configuration||
For containing the impact of a previously forged SAML token, rotate the token-signing AD FS certificate in rapid succession twice, which will invalidate any tokens generated using the previous certificate.
Enable advanced auditing on AD FS. Check the success and failure audit options in the AD FS Management snap-in. Enable Audit Application Generated events on the AD FS farm via Group Policy Object.
|M1026||Privileged Account Management||
Restrict permissions and access to the AD FS server to only originate from privileged access workstations.
|M1018||User Account Management||
Ensure that user accounts with administrative rights follow best practices, including use of privileged access workstations, Just in Time/Just Enough Administration (JIT/JEA), and strong authentication. Reduce the number of users that are members of highly privileged Directory Roles.
This technique may be difficult to detect as SAML tokens are signed by a trusted certificate. The forging process may not be detectable since it is likely to happen outside of a defender's visibility, but subsequent usage of the forged token may be seen. Monitor for anomalous logins using SAML tokens created by a compromised or adversary generated token-signing certificate. These logins may occur on any on-premises resources as well as from any cloud environment that trusts the certificate. Search for logins to service providers using SAML SSO which do not have corresponding 4769, 1200, and 1202 events in the Domain.
Consider modifying SAML responses to include custom elements for each service provider. Monitor these custom elements in service provider access logs to detect any anomalous requests.
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- Bierstock, D., Baker, A. (2019, March 21). I am AD FS and So Can You. Retrieved December 17, 2020.
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