Vulnerability-Lookup

CVE-2026-53424 (GCVE-0-2026-53424)

Vulnerability from cvelistv5 – Published: 2026-08-20 17:27 – Updated: 2026-08-21 19:42

Title

Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions

Summary

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. Samly.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. This issue affects samly: from 0.3.0 onward.

Severity

9.1 (Critical)


                        
                          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

SSVC

Exploitation: none Automatable: yes Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-21 19:41 UTC

CWE

CWE-294 - Authentication Bypass by Capture-replay

Assigner

EEF mitre root

References

2 references

URL	Tags
https://cna.erlef.org/cves/CVE-2026-53424.html	relatedthird-party-advisory
https://osv.dev/vulnerability/EEF-CVE-2026-53424	related

Impacted products

3 products

Vendor	Product	Version
dropbox	samly	Affected: 0.3.0 , < * (semver) cpe:2.3:a:dropbox:samly::::::::
dropbox	samly	Affected: 8a5bb1b4a4753d05470da2036323477f63cfdf4c , < * (git) cpe:2.3:a:dropbox:samly::::::::
handnot2	samly	Affected: 8a5bb1b4a4753d05470da2036323477f63cfdf4c , < * (git) cpe:2.3:a:handnot2:samly::::::::

Credits

Mark Madsen Jonatan Männchen / EEF

Show details on NVD website

JSON

To clipboard

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The \u003ccode\u003e/3\u003c/code\u003e arity accepting a \u003ccode\u003eDuplicateFun\u003c/code\u003e exists in \u003ccode\u003eesaml\u003c/code\u003e 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 \u003ccode\u003eSAMLResponse\u003c/code\u003e obtained from the network, from browser history, or from logs can submit the identical bytes repeatedly until the assertion\u0027s \u003ccode\u003eNotOnOrAfter\u003c/code\u003e passes, each time establishing a session as the assertion\u0027s subject.\u003c/p\u003e\\n\u003cp\u003eThis issue affects samly: from 0.3.0 onward.\u003c/p\u003e\"}, {\"base64\": false, \"type\": \"text/markdown\", \"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\\n`Samly.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\u0027s `NotOnOrAfter` passes, each time establishing a session as the assertion\u0027s subject.\\n\\nThis issue affects samly: from 0.3.0 onward.\"}], \"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\u0027s NotOnOrAfter passes, each time establishing a session as the assertion\u0027s subject.\\n\\nThis issue affects samly: from 0.3.0 onward.\"}], \"impacts\": [{\"capecId\": \"CAPEC-60\", \"descriptions\": [{\"lang\": \"en\", \"value\": \"CAPEC-60 Reusing Session IDs (aka Session Replay)\"}]}], \"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\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-08-20T18:37:24.439Z\"}, \"references\": [{\"tags\": [\"related\", \"third-party-advisory\"], \"url\": \"https://cna.erlef.org/cves/CVE-2026-53424.html\"}, {\"tags\": [\"related\"], \"url\": \"https://osv.dev/vulnerability/EEF-CVE-2026-53424\"}], \"source\": {\"discovery\": \"UNKNOWN\"}, \"title\": \"Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions\"}, \"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-53424\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"yes\"}, {\"Technical Impact\": \"total\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-08-21T19:41:30.269903Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-08-21T19:41:38.301Z\"}}]}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-53424\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"state\": \"PUBLISHED\", \"assignerShortName\": \"EEF\", \"dateReserved\": \"2026-06-09T11:01:47.529Z\", \"datePublished\": \"2026-08-20T17:27:11.115Z\", \"dateUpdated\": \"2026-08-21T19:42:21.623Z\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}

FKIE_CVE-2026-53424

Vulnerability from fkie_nvd - Published: 2026-08-20 18:16 - Updated: 2026-08-21 20:16

Severity

9.1 (Critical) - 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

Summary

References

	URL	Tags
	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	https://cna.erlef.org/cves/CVE-2026-53424.html
	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	https://osv.dev/vulnerability/EEF-CVE-2026-53424

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "collectionURL": "https://repo.hex.pm",
          "cpes": [
            "cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "unaffected",
          "modules": [
            "\u0027Elixir.Samly.Helper\u0027"
          ],
          "packageName": "samly",
          "packageURL": "pkg:hex/samly",
          "product": "samly",
          "programFiles": [
            "lib/samly/helper.ex"
          ],
          "programRoutines": [
            {
              "name": "\u0027Elixir.Samly.Helper\u0027:decode_idp_auth_resp/3"
            }
          ],
          "repo": "https://github.com/dropbox/samly",
          "vendor": "dropbox",
          "versions": [
            {
              "lessThan": "*",
              "status": "affected",
              "version": "0.3.0",
              "versionType": "semver"
            }
          ]
        },
        {
          "collectionURL": "https://github.com",
          "cpes": [
            "cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "unaffected",
          "modules": [
            "\u0027Elixir.Samly.Helper\u0027"
          ],
          "packageName": "dropbox/samly",
          "packageURL": "pkg:github/dropbox/samly",
          "product": "samly",
          "programFiles": [
            "lib/samly/helper.ex"
          ],
          "programRoutines": [
            {
              "name": "\u0027Elixir.Samly.Helper\u0027:decode_idp_auth_resp/3"
            }
          ],
          "repo": "https://github.com/dropbox/samly",
          "vendor": "dropbox",
          "versions": [
            {
              "lessThan": "*",
              "status": "affected",
              "version": "8a5bb1b4a4753d05470da2036323477f63cfdf4c",
              "versionType": "git"
            }
          ]
        },
        {
          "collectionURL": "https://github.com",
          "cpes": [
            "cpe:2.3:a:handnot2:samly:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "unaffected",
          "modules": [
            "\u0027Elixir.Samly.Helper\u0027"
          ],
          "packageName": "handnot2/samly",
          "packageURL": "pkg:github/handnot2/samly",
          "product": "samly",
          "programFiles": [
            "lib/samly/helper.ex"
          ],
          "programRoutines": [
            {
              "name": "\u0027Elixir.Samly.Helper\u0027:decode_idp_auth_resp/3"
            }
          ],
          "repo": "https://github.com/handnot2/samly",
          "vendor": "handnot2",
          "versions": [
            {
              "lessThan": "*",
              "status": "affected",
              "version": "8a5bb1b4a4753d05470da2036323477f63cfdf4c",
              "versionType": "git"
            }
          ]
        }
      ],
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"
    }
  ],
  "cveTags": [],
  "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\u0027s NotOnOrAfter passes, each time establishing a session as the assertion\u0027s subject.\n\nThis issue affects samly: from 0.3.0 onward."
    }
  ],
  "id": "CVE-2026-53424",
  "lastModified": "2026-08-21T20:16:36.470",
  "metrics": {
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 9.1,
          "baseSeverity": "CRITICAL",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "NONE",
          "vulnConfidentialityImpact": "HIGH",
          "vulnIntegrityImpact": "HIGH",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-53424",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-21T19:41:30.269903Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-20T18:16:27.680",
  "references": [
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "url": "https://cna.erlef.org/cves/CVE-2026-53424.html"
    },
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-53424"
    }
  ],
  "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-294"
        }
      ],
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "type": "Secondary"
    }
  ]
}

GHSA-5X87-GF34-8WW7

Vulnerability from github – Published: 2026-08-20 18:30 – Updated: 2026-08-20 18:30

Details

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.

Samly.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.

This issue affects samly: from v0.3.0 onward.

Severity

9.1 (Critical)


                  
                    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

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-53424"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-294"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-20T18:16:27Z",
    "severity": "CRITICAL"
  },
  "details": "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\u0027s NotOnOrAfter passes, each time establishing a session as the assertion\u0027s subject.\n\nThis issue affects samly: from v0.3.0 onward.",
  "id": "GHSA-5x87-gf34-8ww7",
  "modified": "2026-08-20T18:30:59Z",
  "published": "2026-08-20T18:30:59Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-53424"
    },
    {
      "type": "WEB",
      "url": "https://cna.erlef.org/cves/CVE-2026-53424.html"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-53424"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-53424 (GCVE-0-2026-53424)

FKIE_CVE-2026-53424

GHSA-5X87-GF34-8WW7

Tags

Sightings

Nomenclature