CVE-2026-123802: SuperTokens Core SAML: identity taken from an assertion that never passed the audience check, allowing sign-in as any IdP user

SuperTokens Core is an open source authentication server. From 11.3.0 until 11.3.8, 11.4.8, 12.0.11, 12.1.2, 12.2.1, and 12.3.1, a licensed deployment with a configured SAML client can authenticate an identity from an assertion that did not satisfy the audience check. When the identity provider uses assertion-level signing, an attacker who has a still-valid IdP-signed assertion naming the victim for any audience and the attacker's own valid assertion for the target audience can combine them because validateSamlResponseAudience accepts an audience from one assertion while extractAllClaims takes the final NameID and attributes from another; response-level signing does not expose this multi-assertion variant. Independently, an assertion from an identity provider configured for the target deployment but issued to another SuperTokens deployment using the shared default samlspentityid can satisfy the target's audience check. Successful exploitation authenticates the attacker as the victim IdP user. This issue is fixed in versions 11.3.8, 11.4.8, 12.0.11, 12.1.2, 12.2.1, and 12.3.1.