robrichards/xmlseclibs has an Libxml2 Canonicalization error which can bypass Digest/Signature validation
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.
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 form: If an empty string has been signed once (e.g., in a prior interaction or via a misconfigured flow), that signature can potentially be replayed to bypass authentication.
Suggested remediation
Treat canonicalization failures (exceptions or nil/empty outputs) as fatal and abort validation. Add explicit checks: reject when canonicalize returns nil/empty or raise
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | robrichards/xmlseclibs | < 3.1.4 | 3.1.4 |
References
- https://github.com/robrichards/xmlseclibs/security/advisories/GHSA-c4cc-x928-vjw9
- https://nvd.nist.gov/vuln/detail/CVE-2025-66578
- https://github.com/robrichards/xmlseclibs/commit/69fd63080bc47a8d51bc101c30b7cb756862d1d6
- https://github.com/robrichards/xmlseclibs
- https://github.com/robrichards/xmlseclibs/blob/f4131320c6dcd460f1b0c67f16f8bf24ce4b5c3e/src/XMLSecurityDSig.php#L296
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:L/A:L- Weakness (CWE)
CWE-248- Platform
- Composer
- Package
robrichards/xmlseclibs- Disclosed
- 08.12.2025
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-c4cc-x928-vjw9 - CC BY 4.0
Vulnerability history: robrichards/xmlseclibs
All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 4
- First → latest
- 11.2019 03.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 3
- Medium 1
Disclosures per year
- 2019: 1
- 2020: 0
- 2021: 0
- 2022: 0
- 2023: 0
- 2024: 1
- 2025: 1
- 2026: 1
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robrichards/xmlseclibs has an Libxml2 Canonicalization error which can bypass Digest/Signature validation this entry
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