CVE-2026-13397 in HTML::Bare
Summary
by MITRE • 07/16/2026
HTML::Bare versions through 0.04 for Perl will hang in an infinite loop when parsing malformed attributes.
The parserc_parse function never advances the attribute-parse state cursor on certain malformed attribute forms, looping forever.
Nameless attributes such as "<a ='c'>" or unbalanced quotes "<a b='''''''c'>" can trigger this condition.
Note that the latest version available on CPAN is version 0.02. Newer versions are available on the git repository.
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Analysis
by VulDB Data Team • 07/16/2026
The HTML::Bare Perl module presents a critical denial of service vulnerability through an infinite loop in its parsing mechanism. This flaw affects versions through 0.04 and manifests when the parser encounters malformed HTML attributes that do not conform to standard syntax requirements. The vulnerability stems from the parserc_parse function which fails to properly advance its internal state cursor during attribute parsing operations, creating a condition where the parser becomes trapped in an endless loop.
The technical implementation of this vulnerability occurs within the core parsing logic where attribute validation and state management collide. When the parser encounters nameless attributes such as empty strings or unbalanced quote characters, it attempts to process these malformed elements but cannot progress beyond the initial parsing state. This failure to advance the parsing cursor creates an infinite loop condition that consumes system resources and renders the application unresponsive until manually terminated.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable resource exhaustion attacks against systems relying on HTML::Bare for content processing. Attackers can craft malicious HTML input containing specifically formatted malformed attributes that trigger the infinite loop, causing applications using this module to become unresponsive and consume excessive CPU cycles. The vulnerability affects any application that processes user-supplied HTML content through the affected Perl module.
This issue aligns with CWE-835, which describes the weakness of an infinite loop or other endless iteration in software implementations. From an adversarial perspective, the vulnerability maps to ATT&CK technique T1496, representing resource exhaustion attacks where systems are targeted through code execution that consumes excessive computational resources. The vulnerability's exploitation requires only basic knowledge of HTML syntax and does not require advanced privileges or specialized tools.
The recommended mitigation strategy involves immediate upgrading to the latest available version from the git repository, as the CPAN version 0.02 appears to be outdated and does not contain the fixes for this parsing issue. Organizations should implement input validation measures to sanitize HTML content before processing and consider implementing timeouts or resource limits on parsing operations to prevent complete system exhaustion. Additionally, monitoring systems should be configured to detect unusual CPU consumption patterns that may indicate exploitation attempts.
Security teams should also evaluate their existing deployment environments for applications using HTML::Bare and conduct thorough testing of patched versions to ensure compatibility while addressing the denial of service vulnerability. The fix implemented in newer repository versions should include proper state management within the parserc_parse function to guarantee cursor advancement regardless of input format, thereby preventing the infinite loop condition that characterizes this vulnerability.
The broader implications suggest that similar parsing vulnerabilities may exist in other HTML processing libraries and that developers should implement rigorous testing for edge cases and malformed inputs during software development phases. This vulnerability demonstrates how seemingly minor parsing flaws can create significant operational risks when deployed in production environments where user input processing is involved, emphasizing the importance of comprehensive security testing across all input handling components within application stacks.