xmlseclibs, Authentication Bypass, CVE-2025-66578 (Critical)

By /

Listen to this Post

How the CVE Works

  1. The `xmlseclibs` PHP library uses libxml2 to canonicalize (standardize) XML data during signature validation.
  2. A flaw exists when processing specifically crafted, invalid XML input.
  3. When libxml2’s `C14N()` canonicalization function receives this malformed input, it fails silently.
  4. Instead of throwing an error or returning a failure state, it returns an empty string.
  5. The `xmlseclibs` code does not properly check the output of the canonicalization process.
  6. It proceeds to compute a cryptographic digest (the DigestValue) over this empty string.
  7. This computed digest is then compared against the `DigestValue` provided in the XML signature.
  8. An attacker can craft an XML signature where the `DigestValue` is calculated for an empty string.
  9. The library’s validation logic will find a match between the computed and provided digest.
  10. Consequently, it incorrectly validates the cryptographic signature as genuine.
  11. This allows an attacker to bypass authentication or integrity checks.
  12. The system accepts tampered or forged XML documents as if they were properly signed.
  13. The vulnerability is rooted in the missing error handling between libxml2 and xmlseclibs.
  14. The fix in version 3.1.4 adds explicit checks for nil or empty canonicalization output.
  15. It treats these cases as validation failures, preventing the bypass.

DailyCVE Form

Platform: xmlseclibs
Version: 3.1.3
Vulnerability: Authentication Bypass
Severity: Critical
Date: 2025-12-12

Prediction: 2025-01-20 Patch

What Undercode Say:

Check if xmlseclibs is installed via Composer
composer show robrichards/xmlseclibs | grep version
Sample vulnerable PHP code snippet
$doc = new DOMDocument();
$doc->loadXML($malformedXML);
$objDSig = new XMLSecurityDSig();
$objDSig->locateSignature($doc);
Missing check for canonicalization failure occurs here
$objDSig->validateReference();

How Exploit:

  1. Attacker creates a malicious XML document with invalid structure.
  2. They calculate the `DigestValue` for an empty string.
  3. They place this value and a valid signature (for the empty data) in the document.
  4. The victim’s application validates the document using vulnerable xmlseclibs.

5. Canonicalization fails, returning empty string.

  1. The computed digest matches the attacker’s provided DigestValue.

7. Signature validation passes, bypassing authentication.

Protection from this CVE

  • Update `xmlseclibs` to version 3.1.4 immediately.
  • Implement pre-validation to reject malformed XML inputs.
  • Add application-level checks to abort if canonicalization yields empty output.

Impact:

  • Complete authentication bypass in systems relying on XML signatures.
  • Acceptance of forged or tampered data.
  • Potential for unauthorized access or data manipulation.

🎯Let’s Practice Exploiting & Learn Patching For Free:

Sources:

Reported By: nvd.nist.gov
Extra Source Hub:
Undercode

🔐JOIN OUR CYBER WORLD [ CVE News • HackMonitor • UndercodeNews ]

💬 Whatsapp | 💬 Telegram

📢 Follow DailyCVE & Stay Tuned:

𝕏 formerly Twitter 🐦 | @ Threads | 🔗 Linkedin Featured Image

Scroll to Top