SimpleSAMLphp SAML2 library has incorrect signature verification for HTTP-Redirect binding

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

• simplesamlphp saml2

  • < 4.17.0, >= 5.0.0-alpha.1, < 5.0.0-alpha.20affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Other highest-scoring records for the same primary product.

• CVE-2026-49283SimpleSAMLphp HTTP-Artifact TLS validator confusion allows cross-IdP authentication bypass
  34Monitor
• CVE-2024-52806SimpleSAMLphp SAML2 has an XXE in parsing SAML messages
  33Monitor
• CVE-2018-6519The SAML2 library before 1.10.4, 2.x before 2.3.5, and 3.x before 3.1.1 in SimpleSAMLphp has a Regular Expression Denial of Service vulnerab
  31Monitor
• CVE-2026-49289SimpleSAMLphp SAML2: Possible DoS via XPath Transform
  30Monitor
• CVE-2023-49087Validation of SignedInfo
  30Monitor

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Root cause

The verifier takes the algorithm to verify with from the token’s own header. Untrusted data ends up deciding its own verification rule.

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

1const claims = jwt.verify(token, publicKey);

1const claims = jwt.verify(token, publicKey, {2  algorithms: ["RS256"],3  issuer: "https://id.example.com",4  audience: "portal",5});

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.