{"id":"EEF-CVE-2026-53425","summary":"Missing InResponseTo validation in Samly allows acceptance of unsolicited SAML responses","details":"## Summary\n\nInsufficient Verification of Data Authenticity vulnerability in dropbox samly allows an attacker to establish an authenticated session using a SAML response the service provider never requested.\n\n`Samly.SPHandler.validate_authresp/3` in `lib/samly/sp_handler.ex` validates a SAML response for the SP-initiated flow by comparing only the `RelayState` value, the IdP identifier, and the presence of a target URL held in the session. It never compares `SubjectConfirmationData/@InResponseTo` against the ID of the `AuthnRequest` the service provider issued, and that request ID is never persisted, so no comparison is possible. SAML 2.0 Core section 4.1.4.3 requires a service provider to reject a response whose `InResponseTo` does not match a request it made. The underlying `esaml` library checks status, signature, recipient, audience, and staleness, but likewise never inspects `InResponseTo`, so nothing else closes the gap. Exploitation requires a validly signed assertion from the trusted IdP, which an attacker can obtain for their own account, and a `RelayState` matching the victim's session; the assertion signature itself remains intact, so this is not a signature-forgery issue.\n\nThis issue affects samly: from 0.3.0 onward.","aliases":["CVE-2026-53425"],"modified":"2026-09-08T05:30:36.652967614Z","published":"2026-08-20T17:26:35.537Z","database_specific":{"cwe_ids":["CWE-345"],"capec_ids":["CAPEC-62"],"cpe_ids":["cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*","cpe:2.3:a:handnot2:samly:*:*:*:*:*:*:*:*"]},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-53425.html"},{"type":"PACKAGE","url":"https://hex.pm/packages/samly"}],"affected":[{"package":{"name":"samly","ecosystem":"Hex","purl":"pkg:hex/samly"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.3.0"}]}],"versions":["0.10.0","0.10.1","0.4.0","0.5.0","0.6.0","0.6.1","0.6.2","0.6.3","0.7.0","0.7.1","0.7.2","0.8.0","0.8.1","0.8.2","0.8.3","0.8.4","0.9.0","0.9.1","0.9.2","0.9.3","1.0.0","1.0.0-rc.0","1.0.0-rc.1","1.1.0","1.2.0","1.3.0","1.4.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-53425.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/dropbox/samly","events":[{"introduced":"8a5bb1b4a4753d05470da2036323477f63cfdf4c"}]}],"versions":["v1.0.0","v1.0.0-rc.1","v1.0.0-rc.0","v0.10.1","v0.10.0","v0.9.3","v0.9.1","v0.9.0","v0.8.4","v0.8.3","v0.8.2","v0.8.1","v0.8.0","v0.7.2","v0.7.1","v0.7.0","v0.6.3","v0.6.2","v0.6.1","v0.6.0","v0.5.0","v0.3.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-53425.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/handnot2/samly","events":[{"introduced":"8a5bb1b4a4753d05470da2036323477f63cfdf4c"}]}],"versions":["v1.0.0","v1.0.0-rc.1","v1.0.0-rc.0","v0.10.1","v0.10.0","v0.9.3","v0.9.1","v0.9.0","v0.8.4","v0.8.3","v0.8.2","v0.8.1","v0.8.0","v0.7.2","v0.7.1","v0.7.0","v0.6.3","v0.6.2","v0.6.1","v0.6.0","v0.5.0","v0.3.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-53425.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"}],"credits":[{"name":"Mark Madsen","type":"REPORTER"},{"name":"Jonatan Männchen / EEF","type":"COORDINATOR"}]}