Authentication bypass via missing InResponseTo check
Published Aug 20, 2026 · Updated Aug 20, 2026
Authentication bypass in Dropbox Samly 0.3.0 and later allows remote attackers to establish a session with an unsolicited SAML response. Samly.SPHandler.validate_authresp/3 in lib/samly/sp_handler.ex accepts SP-initiated login responses after checking RelayState, the IdP, and a session target URL, but it never stores or compares SubjectConfirmationData/@InResponseTo to the AuthnRequest ID issued by the service provider. Exploitation requires a validly signed assertion from the trusted IdP and a RelayState that matches the victim's session, enabling session swapping rather than signature forgery or IdP compromise.
Summary
What happened
Authentication bypass in Dropbox Samly 0.3.0 and later allows remote attackers to establish a session with an unsolicited SAML response. Samly.SPHandler.validate_authresp/3 in lib/samly/sp_handler.ex accepts SP-initiated login responses after checking RelayState, the IdP, and a session target URL, but it never stores or compares SubjectConfirmationData/@InResponseTo to the AuthnRequest ID issued by the service provider. Exploitation requires a validly signed assertion from the trusted IdP and a RelayState that matches the victim's session, enabling session swapping rather than signature forgery or IdP compromise.
The record
- CVE
- CVE-2026-53425
- Published
- Aug 20, 2026
- Updated
- Aug 20, 2026
- Vendor
- Dropbox
- Product
- Samly
- Classifications
- CWE-345, CAPEC-62
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 20, 2026CVE publishedPublication date reported by the CVE source.
- Aug 20, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0.3.0 <*
- Affected versionversion=8a5bb1b4a4753d05470da2036323477f63cfdf4c <*
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
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
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo