# CVE-2026-53424

## Summary

- **CVE ID:** CVE-2026-53424
- **Severity:** CRITICAL
- **CVSS Score:** 9.1 (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-294
- **Published:** Aug 20, 2026
- **Last Modified:** Aug 21, 2026

## 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 Products

- dropbox — samly (0.3.0)
- dropbox — samly (8a5bb1b4a4753d05470da2036323477f63cfdf4c)
- handnot2 — samly (8a5bb1b4a4753d05470da2036323477f63cfdf4c)

## References

- [CNA](https://cna.erlef.org/cves/CVE-2026-53424.html)
- [CNA](https://osv.dev/vulnerability/EEF-CVE-2026-53424)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.34%
- **EPSS Percentile:** 27.5

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._