CVE-2025-40934 is a critical security vulnerability affecting the TIMLEGGE XML::Sig Perl module versions 0.27 through 0.67. XML::Sig is designed to validate cryptographic signatures on XML documents to ensure their authenticity and integrity. However, due to improper verification logic (classified under CWE-347: Improper Verification of Cryptographic Signature), the module incorrectly validates XML files that have had their signatures removed. Instead of returning an error or failure when no signature is present, the affected versions return a successful validation result. This flaw allows an attacker to strip the signature from an XML document and have it accepted as valid by the system relying on XML::Sig, effectively bypassing signature verification. The vulnerability requires no privileges or user interaction and can be exploited remotely by submitting manipulated XML documents. The CVSS v3.1 score of 9.3 indicates a critical severity, with a network attack vector, low attack complexity, no privileges required, no user interaction, and a scope change due to the potential for widespread impact. The primary impact is on data integrity, as attackers can inject or modify XML content without detection, potentially leading to unauthorized actions, data corruption, or privilege escalation in systems that trust XML::Sig validation. No known exploits are currently reported in the wild, but the high severity and ease of exploitation make this a significant threat. No official patches are listed yet, so mitigation may require additional validation layers or disabling XML::Sig usage until a fix is released.

For European organizations, especially those in sectors that rely heavily on XML for secure data exchange—such as finance, government, healthcare, and critical infrastructure—this vulnerability poses a severe risk. Attackers can exploit this flaw to bypass signature verification, potentially injecting malicious XML payloads that could alter transactions, manipulate configurations, or escalate privileges within applications. This undermines trust in digital signatures and can lead to data integrity breaches, unauthorized access, and operational disruptions. Given the widespread use of Perl in legacy systems and backend processes in Europe, organizations may have unpatched systems vulnerable to this attack. The critical severity and network exploitability mean attackers can remotely compromise systems without authentication, increasing the likelihood of targeted attacks or automated exploitation campaigns. The lack of a patch at the time of disclosure further elevates the risk, necessitating immediate compensating controls to prevent exploitation.

1. Immediately audit all systems and applications using the TIMLEGGE XML::Sig Perl module, identifying versions between 0.27 and 0.67. 2. Where possible, disable or replace XML::Sig usage with alternative, verified XML signature validation libraries that correctly enforce signature presence and validation. 3. Implement additional application-layer checks to verify the presence and validity of XML signatures before processing or accepting XML documents. 4. Employ strict input validation and XML schema validation to detect and reject unsigned or malformed XML documents. 5. Monitor network traffic and application logs for anomalous XML documents lacking signatures or exhibiting suspicious patterns. 6. Prepare to apply vendor patches or updates as soon as they become available, and subscribe to vendor security advisories. 7. Consider deploying Web Application Firewalls (WAFs) with custom rules to detect and block unsigned XML payloads. 8. Educate developers and system administrators about the risks of improper signature validation and encourage secure coding practices around XML processing.