CVE-2026-53424
CVE-2026-53424 is a critical-severity vulnerability with a CVSS 4.0 base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-294.
Key facts
- Severity: Critical (CVSS 4.0 base score 9.1)
- EPSS exploit prediction: 0% (28th percentile)
- Actively exploited: Not listed in CISA KEV
- Weakness: CWE-294
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2026-53424?
- 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.
- How severe is CVE-2026-53424?
- CVE-2026-53424 has a CVSS 4.0 base score of 9.1, rated critical severity.
- Is CVE-2026-53424 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.
- How do I fix CVE-2026-53424?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
- When was CVE-2026-53424 published?
- CVE-2026-53424 was published on 2026-08-20 and last updated on 2026-08-21.
References
Other CWE-294 (Authentication Bypass by Capture-replay) vulnerabilities
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- CVE-2026-28564 — Critical (CVSS 9.8): Insufficient Session Expiration, Authentication Bypass by Capture-replay vulnerability in Apache IoTDB. REST Basic…
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Browse all CWE-294 (Authentication Bypass by Capture-replay) vulnerabilities →