CVE-2026-53425: samly Vulnerability (CVSS 7.6)

Description

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.

Metrics

CVSS 4.0

7.6/10

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/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

EPSS Probability

0.18%

7.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-345

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
dropbox	samly	>= 0.3.0, < *
dropbox	samly	>= 8a5bb1b4a4753d05470da2036323477f63cfdf4c, < *
handnot2	samly	>= 8a5bb1b4a4753d05470da2036323477f63cfdf4c, < *

References

Timeline

Published: Aug 20, 2026
Last Modified: Aug 24, 2026
Status: Awaiting Analysis

Frequently Asked Questions

What is 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.

How severe is CVE-2026-53425?

CVE-2026-53425 has a CVSS score of 7.6/10 (HIGH severity). The EPSS model estimates a 0.18% probability of exploitation in the next 30 days.

How do I fix CVE-2026-53425?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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