{"id":"CVE-2026-53424","state":"PUBLISHED","title":"Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions","description":"Authentication Bypass by Capture-replay vulnerability in dropbox samly allows an attacker to authenticate as the subject of a captured SAML assertion by resubmitting it.\n\nSamly.Helper.decode_idp_auth_resp/3 in lib/samly/helper.ex calls esaml_sp:validate_assertion/2, whose default duplicate detector is a no-op. The /3 arity accepting a DuplicateFun exists in esaml and implements the check, but Samly never calls it and offers no configuration to supply one, so the SAML 2.0 Web Browser SSO Profile requirement that a bearer assertion be used once is unenforced. An attacker holding a valid SAMLResponse obtained from the network, from browser history, or from logs can submit the identical bytes repeatedly until the assertion's NotOnOrAfter passes, each time establishing a session as the assertion's subject.\n\nThis issue affects samly: from 0.3.0 onward.","publishedAt":"2026-08-20T17:27:11.115Z","updatedAt":"2026-08-21T19:42:21.623Z","severity":{"score":9.1,"label":"Critical","version":"4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/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.Helper'"],"programFiles":["lib/samly/helper.ex"],"programRoutines":[{"name":"'Elixir.Samly.Helper':decode_idp_auth_resp/3"}],"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.Helper'"],"programFiles":["lib/samly/helper.ex"],"programRoutines":[{"name":"'Elixir.Samly.Helper':decode_idp_auth_resp/3"}],"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.Helper'"],"programFiles":["lib/samly/helper.ex"],"programRoutines":[{"name":"'Elixir.Samly.Helper':decode_idp_auth_resp/3"}],"repo":"https://github.com/handnot2/samly"}],"references":["https://cna.erlef.org/cves/CVE-2026-53424.html","https://osv.dev/vulnerability/EEF-CVE-2026-53424"],"weaknesses":["CWE-294"],"ingestedAt":"2026-10-29T20:12:16.098Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/53xxx/CVE-2026-53424.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-53424","state":"PUBLISHED","datePublished":"2026-08-20T17:27:11.115Z","dateUpdated":"2026-08-21T19:42:21.623Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-06-09T11:01:47.529Z"},"containers":{"cna":{"title":"Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions","descriptions":[{"lang":"en","value":"Authentication Bypass by Capture-replay vulnerability in dropbox samly allows an attacker to authenticate as the subject of a captured SAML assertion by resubmitting it.\n\nSamly.Helper.decode_idp_auth_resp/3 in lib/samly/helper.ex calls esaml_sp:validate_assertion/2, whose default duplicate detector is a no-op. The /3 arity accepting a DuplicateFun exists in esaml and implements the check, but Samly never calls it and offers no configuration to supply one, so the SAML 2.0 Web Browser SSO Profile requirement that a bearer assertion be used once is unenforced. An attacker holding a valid SAMLResponse obtained from the network, from browser history, or from logs can submit the identical bytes repeatedly until the assertion's NotOnOrAfter passes, each time establishing a session as the assertion's subject.\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.Helper'"],"programFiles":["lib/samly/helper.ex"],"programRoutines":[{"name":"'Elixir.Samly.Helper':decode_idp_auth_resp/3"}],"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.Helper'"],"programFiles":["lib/samly/helper.ex"],"programRoutines":[{"name":"'Elixir.Samly.Helper':decode_idp_auth_resp/3"}],"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.Helper'"],"programFiles":["lib/samly/helper.ex"],"programRoutines":[{"name":"'Elixir.Samly.Helper':decode_idp_auth_resp/3"}],"repo":"https://github.com/handnot2/samly"}],"references":[{"url":"https://cna.erlef.org/cves/CVE-2026-53424.html","tags":["related","third-party-advisory"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-53424","tags":["related"]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":9.1,"baseSeverity":"CRITICAL","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/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-294","description":"CWE-294 Authentication Bypass by Capture-replay","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-08-20T18:37:24.439Z"},"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-60","descriptions":[{"lang":"en","value":"CAPEC-60 Reusing Session IDs (aka Session Replay)"}]}],"source":{"discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-21T19:41:30.269903Z","id":"CVE-2026-53424","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-21T19:42:21.623Z"}}]}}}