Perl MIME-tools: Header parsing vulnerabilities (CVE-2026-116264, CVE-2026-116265, CVE-2026-116266)

The Perl MIME-tools library (versions prior to 5.521) contains multiple vulnerabilities related to the improper parsing of MIME headers. These issues, identified as CVE-2026-116264, CVE-2026-116265, and CVE-2026-116266, allow attackers to manipulate Content-Type parameters and multipart boundaries. Such manipulation can result in parameter hiding or ambiguous parsing, which may lead to security policy bypasses or desynchronization attacks when downstream components or mail filters process the malformed messages.

Impact

The vulnerabilities allow for the crafting of MIME messages that deceive parsers regarding the structure and content of the message body. This can be exploited to bypass security filters that rely on MIME-tools for identifying multipart boundaries or content types, potentially allowing malicious payloads to reach intended destinations by evading inspection.

Recommendation

• Update the Perl MIME-tools library to version 5.521 or later on all systems using this component.
• Audit applications that process external email or MIME-encoded content for reliance on MIME-tools for security-critical parsing or filtering decisions.
• Monitor for mail or web traffic logs showing anomalous Content-Type headers or RFC 2231 continuation patterns if high-risk parsing environments are in use.