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

Description (CNA)

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 (CNA)

Vendor / product	Versions
dropbox / samly	affected 0.3.0 before *
dropbox / samly	affected 8a5bb1b4a4753d05470da2036323477f63cfdf4c before *
handnot2 / samly	affected 8a5bb1b4a4753d05470da2036323477f63cfdf4c before *

CWE

CWE-294

References

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.