robrichards/xmlseclibs has an Libxml2 Canonicalization error which can bypass Digest/Signature validation

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.0 · CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:L/A:L

EPSS

• CVE-2025-66578: 0.24% estimated exploitation activity in the next 30 days; percentile 15.15 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary An authentication bypass vulnerability exists due to a flaw in the libxml2 canonicalization process, which is used by xmlseclibs during document transformation. This weakness allows an attacker to generate a valid signature once and reuse it indefinitely. In practice, a signature created during a previous interaction - or through a misconfigured authentication flow - can be replayed to bypass authentication checks. Details 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. https://github.com/robrichards/xmlseclibs/blob/f4131320c6dcd460f1b0c67f16f8bf24ce4b5c3e/src/XMLSecurityDSig.php#L296 Impact Digest bypass: By crafting input that causes canonicalization to yield an empty string, the attacker can manipulate validation to pass incorrectly. Signature replay on empty canonical…

Published by the source

8 Dec 2025, 17:57 UTC

Last modified by the source

9 Dec 2025, 19:17 UTC

Source last checked

26 Oct 2026, 14:35 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-c4cc-x928-vjw9

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# Patch Next advisory brief: CVE-2025-66578

Advisory: robrichards/xmlseclibs has an Libxml2 Canonicalization error which can bypass Digest/Signature validation
IDs: CVE-2025-66578, GHSA-c4cc-x928-vjw9
Record: https://patchnext.com/advisories/cve-2025-66578 (revision 1, source checked 26 Oct 2026, 14:35 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: robrichards/xmlseclibs 3.1.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist robrichards/xmlseclibs: affected <= 3.1.3; fixed in 3.1.4

## Suggested inspection (read-only)
- Packagist robrichards/xmlseclibs: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on robrichards/xmlseclibs.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-c4cc-x928-vjw9 (GitHub-reviewed advisory GHSA-c4cc-x928-vjw9 lists affected ranges: Packagist robrichards/xmlseclibs >=0 <=3.1.3)

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