# CVE-2026-53424: Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions

> CVE-2026-53424: Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions. CVSS 9.1 (CVSS 4.0).

Canonical: https://rewindex.com/cve/CVE-2026-53424
Last updated: 2026-08-24T16:47:56Z

- Published: 2026-08-20 17:27 UTC · Updated: 2026-08-24 16:47 UTC · Assigner: EEF
- CVSS: 9.1 (CVSS 4.0) · Severity: Critical
- EPSS: 0.60%, 49th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-294

## Description

Authentication Bypass by Capture-replay vulnerability in dropbox samly allows an attacker to authenticate as the subject of a captured SAML assertion by resubmitting it. Samly.Helper.decode\_idp\_auth\_resp/3 in lib/samly/helper.ex calls esaml\_sp:validate\_assertion/2, whose default duplicate detector is a no-op. The /3 arity accepting a DuplicateFun exists in esaml and implements the check, but Samly never calls it and offers no configuration to supply one, so the SAML 2.0 Web Browser SSO Profile requirement that a bearer assertion be used once is unenforced. An attacker holding a valid SAMLResponse obtained from the network, from browser history, or from logs can submit the identical bytes repeatedly until the assertion's NotOnOrAfter passes, each time establishing a session as the assertion's subject. 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-2026-53424)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-53424)
- [https://cna.erlef.org/cves/CVE-2026-53424.html](https://cna.erlef.org/cves/CVE-2026-53424.html)
- [https://osv.dev/vulnerability/EEF-CVE-2026-53424](https://osv.dev/vulnerability/EEF-CVE-2026-53424)

---

_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/)_


---
Canonical: https://rewindex.com/cve/CVE-2026-53424 · Markdown: https://rewindex.com/cve/CVE-2026-53424.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-53424 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:17:01.807Z