{"id":"CVE-2026-53425","state":"PUBLISHED","title":"Missing InResponseTo validation in Samly allows acceptance of unsolicited SAML responses","description":"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.","publishedAt":"2026-08-20T17:26:35.537Z","updatedAt":"2026-08-21T19:50:34.320Z","severity":{"score":7.6,"label":"High","version":"4.0","vector":"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","source":"EEF"},"assigner":"EEF","products":["dropbox samly","handnot2 samly"],"affected":[{"vendor":"dropbox","product":"samly","packageName":"samly","packageURL":"pkg:hex/samly","defaultStatus":"unaffected","versions":[{"version":"0.3.0","status":"affected","lessThan":"*","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Samly.SPHandler'"],"programFiles":["lib/samly/sp_handler.ex"],"programRoutines":[{"name":"'Elixir.Samly.SPHandler':consume_signin_response/1"}],"repo":"https://github.com/dropbox/samly"},{"vendor":"dropbox","product":"samly","packageName":"dropbox/samly","packageURL":"pkg:github/dropbox/samly","defaultStatus":"unaffected","versions":[{"version":"8a5bb1b4a4753d05470da2036323477f63cfdf4c","status":"affected","lessThan":"*","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Samly.SPHandler'"],"programFiles":["lib/samly/sp_handler.ex"],"programRoutines":[{"name":"'Elixir.Samly.SPHandler':consume_signin_response/1"}],"repo":"https://github.com/dropbox/samly"},{"vendor":"handnot2","product":"samly","packageName":"handnot2/samly","packageURL":"pkg:github/handnot2/samly","defaultStatus":"unaffected","versions":[{"version":"8a5bb1b4a4753d05470da2036323477f63cfdf4c","status":"affected","lessThan":"*","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:handnot2:samly:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Samly.SPHandler'"],"programFiles":["lib/samly/sp_handler.ex"],"programRoutines":[{"name":"'Elixir.Samly.SPHandler':consume_signin_response/1"}],"repo":"https://github.com/handnot2/samly"}],"references":["https://cna.erlef.org/cves/CVE-2026-53425.html","https://osv.dev/vulnerability/EEF-CVE-2026-53425"],"weaknesses":["CWE-345"],"ingestedAt":"2026-10-29T20:12:16.098Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/53xxx/CVE-2026-53425.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-53425","state":"PUBLISHED","datePublished":"2026-08-20T17:26:35.537Z","dateUpdated":"2026-08-21T19:50:34.320Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-06-09T11:01:47.529Z"},"containers":{"cna":{"title":"Missing InResponseTo validation in Samly allows acceptance of unsolicited SAML responses","descriptions":[{"lang":"en","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."}],"affected":[{"vendor":"dropbox","product":"samly","packageName":"samly","packageURL":"pkg:hex/samly","defaultStatus":"unaffected","versions":[{"version":"0.3.0","status":"affected","lessThan":"*","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Samly.SPHandler'"],"programFiles":["lib/samly/sp_handler.ex"],"programRoutines":[{"name":"'Elixir.Samly.SPHandler':consume_signin_response/1"}],"repo":"https://github.com/dropbox/samly"},{"vendor":"dropbox","product":"samly","packageName":"dropbox/samly","packageURL":"pkg:github/dropbox/samly","defaultStatus":"unaffected","versions":[{"version":"8a5bb1b4a4753d05470da2036323477f63cfdf4c","status":"affected","lessThan":"*","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Samly.SPHandler'"],"programFiles":["lib/samly/sp_handler.ex"],"programRoutines":[{"name":"'Elixir.Samly.SPHandler':consume_signin_response/1"}],"repo":"https://github.com/dropbox/samly"},{"vendor":"handnot2","product":"samly","packageName":"handnot2/samly","packageURL":"pkg:github/handnot2/samly","defaultStatus":"unaffected","versions":[{"version":"8a5bb1b4a4753d05470da2036323477f63cfdf4c","status":"affected","lessThan":"*","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:handnot2:samly:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Samly.SPHandler'"],"programFiles":["lib/samly/sp_handler.ex"],"programRoutines":[{"name":"'Elixir.Samly.SPHandler':consume_signin_response/1"}],"repo":"https://github.com/handnot2/samly"}],"references":[{"url":"https://cna.erlef.org/cves/CVE-2026-53425.html","tags":["related","third-party-advisory"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-53425","tags":["related"]}],"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":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-08-20T18:38:13.727Z"},"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*","versionStartIncluding":"0.3.0","vulnerable":true},{"criteria":"cpe:2.3:a:handnot2:samly:*:*:*:*:*:*:*:*","versionStartIncluding":"0.3.0","vulnerable":true}],"negate":false,"operator":"OR"}],"operator":"AND"}],"credits":[{"lang":"en","type":"reporter","value":"Mark Madsen"},{"lang":"en","type":"coordinator","value":"Jonatan Männchen / EEF"}],"impacts":[{"capecId":"CAPEC-62","descriptions":[{"lang":"en","value":"CAPEC-62 Cross Site Request Forgery"}]}],"source":{"discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","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"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-21T19:50:34.320Z"}}]}}}