medium CVSS 6

CVE-2025-66578·PHP vulnerability

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.

Severity
medium
Software
PHP
Fixed in
3.1.4
Published
2025-12-09

Affected versions

Until: 3.1.4

Fixed in: 3.1.4

How to fix this CVE

Update PHP and the xmlseclibs library to version 3.1.4 or later to resolve an authentication bypass vulnerability in XML signature validation. The vulnerability allows attackers to bypass signature verification when invalid XML input is processed, potentially leading to unauthorized access. Ensure all dependent applications using xmlseclibs are restarted after patching.

sudo dnf update php php-xml

Defensia detects this vulnerability

How to check if you are affected

  1. Check PHP version: php -v
  2. Verify xmlseclibs installation: php -r "echo (class_exists('XMLSecurityDSig') ? 'Installed' : 'Not installed');"
  3. Find xmlseclibs location: find /usr -name 'xmlseclibs.php' -o -name 'XMLSecurityDSig.php' 2>/dev/null
  4. Confirm fix by checking if xmlseclibs version is 3.1.4+: grep -r 'VERSION\|version' /path/to/xmlseclibs/ | grep -i '3\.1\.[4-9]'

FAQ

What is CVE-2025-66578?

CVE-2025-66578 is an authentication bypass vulnerability in xmlseclibs (a PHP library for XML encryption and signatures) where invalid XML input causes canonicalization to return an empty string instead of failing, allowing signature validation to pass on tampered documents.

Is CVE-2025-66578 being actively exploited?

No, CVE-2025-66578 is not currently listed on the CISA Known Exploited Vulnerabilities catalog, and no public exploits have been disclosed at this time.

What versions of PHP are affected by CVE-2025-66578?

PHP applications using xmlseclibs versions up to 3.1.3 are vulnerable. The vulnerability is fixed in xmlseclibs 3.1.4 and later.

How do I check if my server is vulnerable to CVE-2025-66578?

Run: php -r "require '/path/to/xmlseclibs/xmlseclibs.php'; echo 'xmlseclibs loaded';" and verify the xmlseclibs version is below 3.1.4 by inspecting the library's version constant or composer.lock file.

Does Defensia detect CVE-2025-66578?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PHP with xmlseclibs is installed on a monitored server, CVE-2025-66578 will appear in your dashboard with remediation steps.

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References

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