CVE-2025-40934
📋 TL;DR
CVE-2025-40934 is a critical signature validation bypass vulnerability in XML-Sig Perl module versions 0.27 through 0.67. Attackers can remove signatures from XML documents to make them pass verification checks, potentially enabling forged or tampered XML data to be accepted as valid. This affects any Perl application using vulnerable XML-Sig versions for XML signature validation, particularly in SAML, SOAP, or other XML-based security implementations.
💻 Affected Systems
- XML-Sig Perl module
📦 What is this software?
\ by Xml\
⚠️ Risk & Real-World Impact
Worst Case
Complete authentication bypass in SAML/SSO systems, forged authorization tokens, tampered financial transactions, or malicious XML payloads accepted as legitimate signed documents.
Likely Case
Authentication bypass in applications relying on XML signatures for verification, allowing unauthorized access or data manipulation.
If Mitigated
Limited impact if additional validation layers exist, but XML signature verification remains compromised.
🎯 Exploit Status
Exploitation requires only removing signature elements from XML documents, which is trivial. Public proof-of-concept exists in GitHub issues.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.68 or later
Vendor Advisory: https://github.com/perl-net-saml2/perl-XML-Sig/issues/63
Restart Required: Yes
Instructions:
1. Update XML-Sig using CPAN: 'cpan XML::Sig'
2. Or install manually: 'cpanm XML::Sig@0.68'
3. Restart all Perl applications/services using XML-Sig
4. Verify the update with 'perl -MXML::Sig -e "print $XML::Sig::VERSION"'
🔧 Temporary Workarounds
Pre-validation signature check
allAdd custom validation to check for signature elements before calling XML-Sig validation
perl -e 'use XML::LibXML; my $doc = XML::LibXML->load_xml(string => $xml); if (!$doc->findnodes("//*[local-name()='Signature' and namespace-uri()='http://www.w3.org/2000/09/xmldsig#']")) { die "No signature found" }'
🧯 If You Can't Patch
- Implement additional XML schema validation to ensure required signature elements are present
- Deploy network controls to block or inspect XML traffic to vulnerable applications
🔍 How to Verify
Check if Vulnerable:
Check XML-Sig version with: perl -MXML::Sig -e 'print "VERSION: $XML::Sig::VERSION\n"; print "VULNERABLE\n" if $XML::Sig::VERSION >= 0.27 && $XML::Sig::VERSION <= 0.67'Check Version:
perl -MXML::Sig -e 'print $XML::Sig::VERSION'Verify Fix Applied:
Verify version is 0.68 or higher: perl -MXML::Sig -e 'print "VERSION: $XML::Sig::VERSION\n"; print "PATCHED\n" if $XML::Sig::VERSION >= 0.68'📡 Detection & Monitoring
Log Indicators:
- XML validation successes on documents without signature elements
- Unexpected authentication successes in SAML/SSO logs
- XML parsing errors or warnings in application logs
Network Indicators:
- XML traffic to applications using XML-Sig without proper signature elements
- Unusual XML document patterns with missing signature sections
SIEM Query:
source="application.log" AND ("XML validation" OR "signature verification") AND (success OR passed) AND NOT "signature found"