CVE-2026-18108 Auth bypass in Net::SAML2
Attackers can bypass authentication in Perl SAML2 libraries by sending unsigned encrypted assertions, allowing them to impersonate arbitrary users.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-18108?
CVE-2026-18108 is a critical authentication bypass vulnerability in TIMLEGGE Net::SAML2, published on 3 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-347
Which versions are affected by CVE-2026-18108?
It affects 1 product.
Products include Timlegge Net\.
How do I fix CVE-2026-18108?
No fix has been published for CVE-2026-18108 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-18108 being exploited?
There is no known exploitation of CVE-2026-18108 in the wild and no public exploit code.
Other vulnerabilities in TIMLEGGE Net::SAML2
Sources
Also known as GHSA-g48m-j5m7-625h.