{"id":"CVE-2026-49284","aliases":["GHSA-q8r6-xj3f-wrrm"],"url":"https://o3.security/vulnerability/CVE-2026-49284","summary":"SimpleSAMLphp SP accepts a response from an unexpected IdP when unsigned `Response/InResponseTo` is combined with a signed assertion lacking `SubjectConfirmationData/InResponseTo`","details":"## Summary\n\nSimpleSAMLphp's SAML SP ACS path does not enforce the IdP selected for an SP-initiated login. If a saved SP state contains `ExpectedIssuer = IdP A`, but the ACS receives a valid response from `IdP B`, the code logs a warning and continues processing instead of rejecting the response.\n\nThat behavior becomes security-relevant when combined with the response-processing rule that accepts an unsigned `samlp:Response/@InResponseTo` outside the signed assertion whenever the signed assertion's `SubjectConfirmationData` does not carry its own `InResponseTo`. A response issued by one trusted IdP can therefore be bound to SP state created for another IdP.\n\n## Impact\n\nIn a multi-IdP deployment, a lower-trust IdP can satisfy SP state created for a different expected IdP. This can bypass an SP flow that intentionally routes the user to a specific IdP, including deployments that set `enable_unsolicited` to `false` to prevent IdP-initiated logins.\n\nThe impact is highest when the SP trusts multiple IdPs with different assurance levels, tenant boundaries, or attribute namespaces, and application authorization depends on the selected/expected IdP. In those deployments this is an authentication/authorization bypass candidate. Impact strongly depends on whether an attacker can obtain a signed IdP-initiated assertion from a lower-trust trusted IdP and whether the downstream application maps identifiers globally.","published":"2026-07-17T19:17:23.897Z","modified":"2026-08-12T03:51:19.133282010Z","cvss":{"score":7.1,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N"},"epss":{"score":0.00222,"percentile":0.12722,"asOf":"2026-09-06"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"simplesamlphp/simplesamlphp","fixedVersion":"2.5.2"},{"ecosystem":"Packagist","name":"simplesamlphp/simplesamlphp","fixedVersion":"2.4.7"}],"fix":null,"references":[{"type":"WEB","url":"https://github.com/simplesamlphp/simplesamlphp/releases/tag/v2.4.7"},{"type":"WEB","url":"https://github.com/simplesamlphp/simplesamlphp/releases/tag/v2.5.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/49xxx/CVE-2026-49284.json"},{"type":"ADVISORY","url":"https://github.com/simplesamlphp/simplesamlphp/security/advisories/GHSA-q8r6-xj3f-wrrm"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-49284"},{"type":"PACKAGE","url":"https://github.com/simplesamlphp/simplesamlphp"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:19.133282010Z"}}