CVE-2026-53425

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.

CVSS

No CVSS.

References

Link	Resource
https://cna.erlef.org/cves/CVE-2026-53425.html
https://osv.dev/vulnerability/EEF-CVE-2026-53425

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-20 18:16

Updated : 2026-08-24 16:47

NVD link : CVE-2026-53425

Mitre link : CVE-2026-53425

CVE.ORG link : CVE-2026-53425

JSON object : View

Products Affected

No product.

CWE

CWE-345

Insufficient Verification of Data Authenticity

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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."}], "lastModified": "2026-08-24T16:47:56.007", "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}