CVE-2016-10520 in jadedown
Summary
by MITRE
jadedown is vulnerable to regular expression denial of service (ReDoS) when certain types of user input is passed in.
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Analysis
by VulDB Data Team • 02/10/2020
The vulnerability identified as CVE-2016-10520 affects the jadedown library, which is a node.js markdown parser that processes markdown text and converts it to html. This particular vulnerability stems from the library's insufficient validation of user input during the markdown parsing process, creating a potential security risk that can be exploited by malicious actors. The issue manifests when specific types of user-provided input are processed through the library's regular expression patterns, leading to excessive computational resource consumption and potential system instability.
The technical flaw resides in the regular expression patterns used within the jadedown library to parse markdown syntax elements such as links, code blocks, and other formatting constructs. When attackers craft malicious input strings that match the regular expression patterns in a way that causes catastrophic backtracking, the parsing engine becomes trapped in an exponential time complexity scenario. This behavior is characteristic of regular expression denial of service vulnerabilities where the input string is designed to cause the regular expression engine to perform an enormous number of operations, effectively consuming all available processing resources. The vulnerability is classified under CWE-400 as a Regular Expression Denial of Service attack, which specifically targets the computational complexity of regular expression evaluation.
The operational impact of this vulnerability extends beyond simple performance degradation, as it can lead to complete system unavailability and denial of service conditions. When exploited, the vulnerability allows attackers to craft specially formatted markdown content that, when processed by the affected library, consumes excessive CPU cycles and memory resources. This can result in application crashes, system slowdowns, or complete service interruption, particularly in environments where the library is used to process untrusted user input such as comment systems, content management platforms, or collaborative editing tools. The vulnerability is particularly concerning in web applications where markdown processing occurs in real-time, as the attack can be executed with minimal resources and maximum impact.
Mitigation strategies for CVE-2016-10520 should focus on both immediate remediation and long-term architectural improvements. The most effective immediate solution involves updating to a patched version of the jadedown library where the vulnerable regular expressions have been either rewritten to prevent catastrophic backtracking or replaced with more efficient parsing approaches. Organizations should also implement input validation and sanitization measures that limit the length and complexity of user-provided markdown content, particularly when processing untrusted input. Additionally, implementing resource limits and timeouts for parsing operations can help prevent exploitation by limiting the computational resources that can be consumed during markdown processing. The mitigation approach aligns with ATT&CK technique T1499.004 for resource exhaustion and follows defensive practices recommended in the OWASP Top Ten for preventing denial of service vulnerabilities in web applications.