Authentication Bypass Vulnerability in Dropbox's Samly
CVE-2026-53424

9.1CRITICAL

Key Information:

Vendor

Dropbox

Status
Samly
Vendor
CVE Published:
20 August 2026

What is CVE-2026-53424?

The Dropbox Samly library contains an authentication bypass vulnerability that allows attackers to resubmit captured SAML assertions. The default duplicate detector in the library is ineffective, meaning that an attacker can repeatedly use a valid SAMLResponse until its expiration is reached. This behavior fails to comply with the SAML 2.0 Web Browser SSO Profile, which requires that bearer assertions be used only once. As a result, unauthorized authentication sessions can be established using previously captured assertions.

Affected Version(s)

samly 0.3.0

samly 8a5bb1b4a4753d05470da2036323477f63cfdf4c

samly 8a5bb1b4a4753d05470da2036323477f63cfdf4c

References

https://cna.erlef.org/cves/CVE-2026-53424.html
relatedthird-party-advisory
https://osv.dev/vulnerability/EEF-CVE-2026-53424
related

CVSS V4

Score:
9.1
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
Physical
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Mark Madsen
Jonatan Männchen / EEF
.