CVE-2026-53425
HighCVSS 7.6Exploitation Probability (EPSS)
Low risk7th percentile - higher than 7% of all known CVEs
Summary
Samly from version 0.3.0 has a vulnerability of insufficient verification of data authenticity, allowing an attacker to establish an authenticated session using a SAML response the service provider never requested. Validation does not compare the InResponseTo attribute with the AuthnRequest ID.
Risk Assessment
An attacker can gain access to a victim's session using a signed assertion from a trusted IdP, potentially leading to unauthorized access to the application.
Recommendation
Update samly to a patched version or implement additional SAML response validation mechanisms, such as checking InResponseTo.
Other vulnerabilities in samly
Original NVD description (English source)
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.