verify_xml in Net::SAML2::Role::VerifyXML runs "return if !$anchors && !$cacert;" as soon as the XML::Sig check succeeds, and that check uses the X.509 certificate taken from the response's own dsig:KeyInfo/dsig:X509Certificate element, so an unanchored response is checked only against the key it carries. Binding::POST declares cacert as an optional Maybe[Str] with no default, so a POST binding built without one takes that path, and _verify_encrypted_assertion returns early the same way with "return $xml unless $cacert;".
Any caller that constructs Binding::POST or calls Assertion->new_from_xml without a cacert, cert_text, or anchors argument accepts a response signed by an attacker generated key whose self-signed certificate is embedded in that response, authenticating an arbitrary assertion.
Analysis
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Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| TIMLEGGE | Net::SAML2 | unaffected |
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Vendor Solution
Upgrade to Net::SAML2 0.86 or later, which requires a cacert or cert_text trust anchor before a response or assertion signature is verified.
Vendor Workaround
For deployments that cannot upgrade, construct Net::SAML2::Binding::POST, and call Net::SAML2::Protocol::Assertion->new_from_xml, with a cacert, cert_text, or anchors argument identifying the IdP signing certificate.
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Mon, 03 Aug 2026 13:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | Net::SAML2 versions before 0.86 for Perl allow SAML authentication bypass by verifying responses against the response-embedded certificate in verify_xml when no trust anchor is configured. verify_xml in Net::SAML2::Role::VerifyXML runs "return if !$anchors && !$cacert;" as soon as the XML::Sig check succeeds, and that check uses the X.509 certificate taken from the response's own dsig:KeyInfo/dsig:X509Certificate element, so an unanchored response is checked only against the key it carries. Binding::POST declares cacert as an optional Maybe[Str] with no default, so a POST binding built without one takes that path, and _verify_encrypted_assertion returns early the same way with "return $xml unless $cacert;". Any caller that constructs Binding::POST or calls Assertion->new_from_xml without a cacert, cert_text, or anchors argument accepts a response signed by an attacker generated key whose self-signed certificate is embedded in that response, authenticating an arbitrary assertion. | |
| Title | Net::SAML2 versions before 0.86 for Perl allow SAML authentication bypass by verifying responses against the response-embedded certificate in verify_xml when no trust anchor is configured | |
| Weaknesses | CWE-295 CWE-347 |
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MITRE
Status: PUBLISHED
Assigner: CPANSec
Published:
Updated: 2026-08-03T12:42:08.879Z
Reserved: 2026-07-28T16:26:10.967Z
Link: CVE-2026-18089
Vulnrichment
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