What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2025-12-09 · updated 2026-10-07
• Weakness: CWE-248

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.

Affected products

• robrichards xmlseclibs: before 3.1.4 — fixed in 3.1.4

How to fix

Upgrade to a fixed version: robrichards xmlseclibs 3.1.4. Check the vendor advisory for mitigations.

References

• https://github.com/robrichards/xmlseclibs/blob/f4131320c6dcd460f1b0c67f16f8bf24ce4b5c3e/src/XMLSecurityDSig.php#L296
• https://github.com/robrichards/xmlseclibs/commit/69fd63080bc47a8d51bc101c30b7cb756862d1d6
• https://github.com/robrichards/xmlseclibs/security/advisories/GHSA-c4cc-x928-vjw9

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