CVE-2026-53424
Missing one-time-use enforcement in Samly allows replay of SAML bearer assertions
- State
- Published
- Severity
- 9.1 Critical
- Published
- Aug 20, 2026
- Updated
- Aug 21, 2026
- Reserved
- Jun 9, 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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 9.1 Critical | 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 | EEF |
Weaknesses
- CWE-294 Authentication Bypass by Capture-replay
Affected Products
| Product | Versions |
|---|---|
samlydropbox |
|
samlydropbox |
|
samlyhandnot2 |
|
References
- https://cna.erlef.org/cves/CVE-2026-53424.htmlrelatedthird-party-advisory
- https://osv.dev/vulnerability/EEF-CVE-2026-53424related
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