CVE-2026-53424Network attack vector

Authentication bypass via SAML assertion replay

Published Aug 20, 2026 · Updated Aug 20, 2026

Authentication bypass in Dropbox Samly 0.3.0 and later allows remote attackers to log in as another user via replayed SAML assertions. The decode_idp_auth_resp/3 function in lib/samly/helper.ex passes IdP responses to esaml_sp:validate_assertion/2, which uses a default duplicate detector that always returns ok instead of rejecting reused assertions. Attackers need a valid SAMLResponse from network capture, browser history, or logs; replay succeeds only until NotOnOrAfter expires, but each submission creates a new session as the assertion's subject.

CVSS severity9.1
Critical
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Dropbox Samly 0.3.0 and later allows remote attackers to log in as another user via replayed SAML assertions. The decode_idp_auth_resp/3 function in lib/samly/helper.ex passes IdP responses to esaml_sp:validate_assertion/2, which uses a default duplicate detector that always returns ok instead of rejecting reused assertions. Attackers need a valid SAMLResponse from network capture, browser history, or logs; replay succeeds only until NotOnOrAfter expires, but each submission creates a new session as the assertion's subject.

The record

CVE
CVE-2026-53424
Published
Aug 20, 2026
Updated
Aug 20, 2026
Vendor
Dropbox
Product
Samly
Classifications
CWE-294, CAPEC-60, T1550
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.3.0 <*
  2. Affected versionversion=8a5bb1b4a4753d05470da2036323477f63cfdf4c <*

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Dropbox · Samlyversion=0.3.0 <*; version=8a5bb1b4a4753d05470da2036323477f63cfdf4c <*
handnot2 · Samlyversion=8a5bb1b4a4753d05470da2036323477f63cfdf4c <*

Published CVSS scores

9.1EEFCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-294Authentication Bypass by Capture-replay
CAPEC-60Reusing Session IDs (aka Session Replay)
T1550Use Alternate Authentication Material

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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