CVE-2026-18108
CriticalCVSS 9.8Summary
A vulnerability in the Net::SAML2 library for Perl (versions before 0.86) allows SAML authentication bypass. The _verify_encrypted_assertion function accepts a decrypted assertion without a signature, enabling an attacker to send an unsigned assertion encrypted with the SP's certificate and authenticate as any user.
Risk Assessment
Organizations using Net::SAML2 with a decryption key are at risk of unauthorized authentication of any user by an attacker without knowledge of the IdP's private key.
Recommendation
Update the Net::SAML2 library to version 0.86 or later.
Original NVD description (English source)
Net::SAML2 versions before 0.86 for Perl allow authentication bypass because _verify_encrypted_assertion accepts an EncryptedAssertion whose decrypted content carries no signature. _verify_encrypted_assertion decrypts the EncryptedAssertion and returns it as verified when it carries no signature, via "return $xml unless $xpath->exists('dsig:Signature', $assert);". The signature check and the trust anchor check that follow run only when a signature is present, so a decrypted assertion with no dsig:Signature element reaches new_from_xml unverified and its NameID and attributes are read into the assertion object. An SP's encryption certificate is published in its SAML metadata so the IdP can encrypt to it, so any party can encrypt an unsigned assertion to that certificate, wrap it in a samlp:Response, and post it to the assertion consumer service. Any caller that configures a decryption key_file, and so accepts EncryptedAssertions, takes identity fields from an assertion that no trust anchor covers, and an unauthenticated party can authenticate as an arbitrary user. Callers with no key_file configured do not decrypt and are unaffected.