CVE-2025-66578: robrichards/xmlseclibs has an Libxml2 Canonicalization error which can bypass Digest/Signature validation

Vulnerability summary

CVE-2025-66578 is a high (CVSS 7.5) Uncaught Exception vulnerability in robrichards xmlseclibs. EPSS estimates a 0.24% chance of exploitation in the next 30 days, higher than 14.4% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 09-12-2025
   PublishedVulnerability first disclosed.
2. 09-12-2025
   Last modifiedVulnerability information updated.

Description

xmlseclibs is a library written in PHP for working with XML Encryption and Signatures. Versions 3.1.3 contain an authentication bypass vulnerability due to a flaw in the libxml2 canonicalization process during document transformation. When libxml2’s canonicalization is invoked on an invalid XML input, it may return an empty string rather than a canonicalized node. xmlseclibs then proceeds to compute the DigestValue over this empty string, treating it as if canonicalization succeeded. This issue is fixed in version 3.1.4. Workarounds include treating canonicalization failures (exceptions or nil/empty outputs) as fatal and aborting validation, and/or adding explicit checks to reject when canonicalize returns nil/empty or raises errors.

• CWE-248Uncaught ExceptionAn exception is thrown from a function, but it is not caught.