Cross-IdP authentication bypass via validator confusion
Published Aug 19, 2026 · Updated Aug 19, 2026
Authentication bypass in SimpleSAMLphp SAML2 before 4.19.3, 4.20.2, 5.0.6, and 6.2.1 allows attackers to impersonate users via HTTP-Artifact responses. In HTTPArtifact::receive(), the outer SOAP ArtifactResponse gets a TLS-based validator, but the embedded SAML Response is later checked against metadata chosen from its own issuer, and SOAPClient::validateSSL() returns without error when the compared key does not match. In a multi-IdP federation, a malicious or lower-trust IdP can therefore supply an unsigned Response that claims a higher-trust IdP and authenticate as arbitrary users with attacker-chosen attributes, NameID, and session data.
Summary
What happened
Authentication bypass in SimpleSAMLphp SAML2 before 4.19.3, 4.20.2, 5.0.6, and 6.2.1 allows attackers to impersonate users via HTTP-Artifact responses. In HTTPArtifact::receive(), the outer SOAP ArtifactResponse gets a TLS-based validator, but the embedded SAML Response is later checked against metadata chosen from its own issuer, and SOAPClient::validateSSL() returns without error when the compared key does not match. In a multi-IdP federation, a malicious or lower-trust IdP can therefore supply an unsigned Response that claims a higher-trust IdP and authenticate as arbitrary users with attacker-chosen attributes, NameID, and session data.
The record
- CVE
- CVE-2026-49283
- Published
- Aug 19, 2026
- Updated
- Aug 19, 2026
- Vendor
- SimpleSAMLphp
- Product
- SAML2
- Classifications
- CWE-295, T1199
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 19, 2026CVE publishedPublication date reported by the CVE source.
- Aug 19, 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.
- Affected versionversion=< 4.19.3
- Affected versionversion=>= 4.20.0, < 4.20.2
- Affected versionversion=>= 5.0.0, < 5.0.6
- Affected versionversion=>= 6.0.0, < 6.2.1
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
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Technologies
Your stack
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Your stack
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