CVE-2022-21670 in markdown-it
Summary
by MITRE • 01/11/2022
markdown-it is a Markdown parser. Prior to version 1.3.2, special patterns with length greater than 50 thousand characterss could slow down the parser significantly. Users should upgrade to version 12.3.2 to receive a patch. There are no known workarounds aside from upgrading.
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Analysis
by VulDB Data Team • 01/13/2022
The markdown-it library represents a widely adopted JavaScript implementation for parsing Markdown text into HTML format, serving as a critical component in numerous web applications, content management systems, and documentation tools. This particular vulnerability affects the library's parsing engine and specifically targets its handling of specially crafted input sequences that exceed fifty thousand characters in length. The flaw exists within the core parsing algorithm that processes markdown patterns, creating a performance degradation scenario where the parser becomes significantly slowed down when encountering these extended input sequences. The vulnerability stems from insufficient input validation and inadequate optimization in the parsing routine that fails to efficiently handle unusually long patterns, leading to exponential execution time growth during processing.
The technical implementation of this vulnerability manifests when the parser encounters markdown patterns containing special characters or sequences that exceed the threshold of fifty thousand characters. This condition triggers a parsing behavior that causes the algorithm to enter an inefficient execution path where computational resources are consumed disproportionately. The vulnerability can be classified under CWE-770, which addresses allocation of resources without limits or with inadequate limits, as the parser fails to implement proper bounds checking for input pattern lengths. The parser's performance degrades significantly because it processes these extended patterns using nested loops or recursive operations that scale exponentially with input size rather than maintaining linear or polynomial complexity. This behavior creates a potential denial of service condition where legitimate parsing operations become unresponsive or consume excessive computational resources.
The operational impact of CVE-2022-21670 extends beyond simple performance degradation to encompass broader security implications within web applications that rely on markdown-it for content processing. Attackers could exploit this vulnerability through server-side request manipulation or user input processing where markdown content is rendered, potentially causing service disruption or resource exhaustion attacks. Applications that process untrusted markdown input from users, including blog platforms, wikis, comment systems, and documentation generators, become vulnerable to this attack vector. The vulnerability affects the library's ability to maintain consistent response times and can lead to cascading failures in systems where markdown processing is a core functionality. From an attacker's perspective, this vulnerability aligns with ATT&CK technique T1496, which involves resource exhaustion attacks that can be executed through input manipulation, making it particularly dangerous in environments where markdown processing is exposed to untrusted inputs.
The recommended mitigation strategy involves upgrading to version 1.3.2 or later, which contains the necessary patches to address the parsing inefficiency. The fix implements proper input length validation and optimization techniques to prevent the exponential execution time growth when processing extended patterns. Security practitioners should ensure that all dependent applications and services are updated to use the patched version of markdown-it, as the vulnerability does not have any known workarounds aside from the upgrade path. Organizations should implement comprehensive testing procedures to verify that the upgrade does not introduce any regressions in their markdown processing functionality while ensuring that the performance improvements are effectively realized. Additionally, monitoring systems should be configured to detect unusual parsing behavior that might indicate exploitation attempts, particularly in environments where user-provided markdown content is processed.