# CVE-2026-53425: Missing InResponseTo validation in Samly allows acceptance of unsolicited SAML responses

> CVE-2026-53425: Missing InResponseTo validation in Samly allows acceptance of unsolicited SAML responses. CVSS 7.6 (CVSS 4.0).

Canonical: https://rewindex.com/cve/CVE-2026-53425
Last updated: 2026-08-24T16:47:56Z

- Published: 2026-08-20 17:26 UTC · Updated: 2026-08-24 16:47 UTC · Assigner: EEF
- CVSS: 7.6 (CVSS 4.0) · Severity: High
- EPSS: 0.22%, 13th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-345

## 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.

## Affected vendors and products

- dropbox: samly
- handnot2: samly

## Tracked companies

- [Dropbox](https://rewindex.com/company/dropbox.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-53425)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-53425)
- [https://cna.erlef.org/cves/CVE-2026-53425.html](https://cna.erlef.org/cves/CVE-2026-53425.html)
- [https://osv.dev/vulnerability/EEF-CVE-2026-53425](https://osv.dev/vulnerability/EEF-CVE-2026-53425)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-53425 · Markdown: https://rewindex.com/cve/CVE-2026-53425.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-53425 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:17:03.169Z