Dropbox samly SP Handler lib/samly/sp_handler.ex Samly.SPHandler.validate_authresp data authenticity

Summaryinfo

A vulnerability was found in Dropbox samly. It has been declared as critical. This impacts the function Samly.SPHandler.validate_authresp of the file lib/samly/sp_handler.ex of the component SP Handler. The manipulation results in data authenticity. This vulnerability was named CVE-2026-53425. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability, which was classified as critical, was found in Dropbox samly (version now known). Affected is the function Samly.SPHandler.validate_authresp of the file lib/samly/sp_handler.ex of the component SP Handler. The manipulation with an unknown input leads to a data authenticity vulnerability. CWE is classifying the issue as CWE-345. The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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 v0.3.0 onward.

The advisory is available at cna.erlef.org. This vulnerability is traded as CVE-2026-53425 since 06/09/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. Successful exploitation requires user interaction by the victim. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 08/20/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Type

• Cloud Software

Vendor

• Dropbox

Name

• samly

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