Insufficient 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.
\nSamly.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.
This issue affects samly: from 0.3.0 onward.
" }, { "base64": false, "type": "text/markdown", "value": "Insufficient 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." } ], "value": "Insufficient 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\nSamly.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." } ], "impacts": [ { "capecId": "CAPEC-62", "descriptions": [ { "lang": "en", "value": "CAPEC-62 Cross Site Request Forgery" } ] } ], "metrics": [ { "cvssV4_0": { "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "baseScore": 7.6, "baseSeverity": "HIGH", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "PASSIVE", "valueDensity": "NOT_DEFINED", "vectorString": "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", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "HIGH", "vulnerabilityResponseEffort": "NOT_DEFINED" }, "format": "CVSS", "scenarios": [ { "lang": "en", "value": "GENERAL" } ] } ], "problemTypes": [ { "descriptions": [ { "cweId": "CWE-345", "description": "CWE-345 Insufficient Verification of Data Authenticity", "lang": "en", "type": "CWE" } ] } ], "providerMetadata": { "orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-08-20T18:38:13.727Z" }, "references": [ { "tags": [ "related", "third-party-advisory" ], "url": "https://cna.erlef.org/cves/CVE-2026-53425.html" }, { "tags": [ "related" ], "url": "https://osv.dev/vulnerability/EEF-CVE-2026-53425" } ], "source": { "discovery": "UNKNOWN" }, "title": "Missing InResponseTo validation in Samly allows acceptance of unsolicited SAML responses" }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "timestamp": "2026-08-21T19:50:24.245049Z", "id": "CVE-2026-53425", "options": [ { "Exploitation": "none" }, { "Automatable": "no" }, { "Technical Impact": "total" } ], "role": "CISA Coordinator", "version": "2.0.3" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-08-21T19:50:34.320Z" } } ] } }