CVE-2026-53425 (GCVE-0-2026-53425)

Vulnerability from cvelistv5 – Published: 2026-08-20 17:26 – Updated: 2026-08-20 18:38
VLAI
Title
Missing InResponseTo validation in Samly allows acceptance of unsolicited SAML responses
Summary
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. 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. This issue affects samly: from 0.3.0 onward.
CWE
  • CWE-345 - Insufficient Verification of Data Authenticity
Assigner
References
Impacted products
Vendor Product Version CPE status
dropbox samly Affected: 0.3.0 , < * (semver)
    cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*
Create a notification for this product.
dropbox samly Affected: 8a5bb1b4a4753d05470da2036323477f63cfdf4c , < * (git)
    cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*
Create a notification for this product.
handnot2 samly Affected: 8a5bb1b4a4753d05470da2036323477f63cfdf4c , < * (git)
    cpe:2.3:a:handnot2:samly:*:*:*:*:*:*:*:*
Create a notification for this product.
Show details on NVD website

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      "affected": [
        {
          "collectionURL": "https://repo.hex.pm",
          "cpes": [
            "cpe:2.3:a:dropbox:samly:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "unaffected",
          "modules": [
            "\u0027Elixir.Samly.SPHandler\u0027"
          ],
          "packageName": "samly",
          "packageURL": "pkg:hex/samly",
          "product": "samly",
          "programFiles": [
            "lib/samly/sp_handler.ex"
          ],
          "programRoutines": [
            {
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          "vendor": "dropbox",
          "versions": [
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              "status": "affected",
              "version": "0.3.0",
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          "modules": [
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          "modules": [
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          "type": "reporter",
          "value": "Mark Madsen"
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          "type": "coordinator",
          "value": "Jonatan M\u00e4nnchen / EEF"
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              "value": "\u003cp\u003eInsufficient 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.\u003c/p\u003e\n\u003cp\u003e\u003ccode\u003eSamly.SPHandler.validate_authresp/3\u003c/code\u003e in \u003ccode\u003elib/samly/sp_handler.ex\u003c/code\u003e validates a SAML response for the SP-initiated flow by comparing only the \u003ccode\u003eRelayState\u003c/code\u003e value, the IdP identifier, and the presence of a target URL held in the session. It never compares \u003ccode\u003eSubjectConfirmationData/@InResponseTo\u003c/code\u003e against the ID of the \u003ccode\u003eAuthnRequest\u003c/code\u003e 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 \u003ccode\u003eInResponseTo\u003c/code\u003e does not match a request it made. The underlying \u003ccode\u003eesaml\u003c/code\u003e library checks status, signature, recipient, audience, and staleness, but likewise never inspects \u003ccode\u003eInResponseTo\u003c/code\u003e, 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 \u003ccode\u003eRelayState\u003c/code\u003e matching the victim\u0027s session; the assertion signature itself remains intact, so this is not a signature-forgery issue.\u003c/p\u003e\n\u003cp\u003eThis issue affects samly: from 0.3.0 onward.\u003c/p\u003e"
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              "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\u0027s 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\u0027s 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."
        }
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      "impacts": [
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            "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",
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            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
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            "vulnerabilityResponseEffort": "NOT_DEFINED"
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              "value": "GENERAL"
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          "descriptions": [
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              "description": "CWE-345 Insufficient Verification of Data Authenticity",
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              "type": "CWE"
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      "providerMetadata": {
        "dateUpdated": "2026-08-20T18:38:13.727Z",
        "orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
        "shortName": "EEF"
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        },
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            "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"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
    "assignerShortName": "EEF",
    "cveId": "CVE-2026-53425",
    "datePublished": "2026-08-20T17:26:35.537Z",
    "dateReserved": "2026-06-09T11:01:47.529Z",
    "dateUpdated": "2026-08-20T18:38:13.727Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2",
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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. 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  }
}



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