CVE-2024-28244 in KaTeX
Summary
by MITRE • 03/25/2024
KaTeX is a JavaScript library for TeX math rendering on the web. KaTeX users who render untrusted mathematical expressions could encounter malicious input using `\def` or `\newcommand` that causes a near-infinite loop, despite setting `maxExpand` to avoid such loops. KaTeX supports an option named maxExpand which aims to prevent infinitely recursive macros from consuming all available memory and/or triggering a stack overflow error. Unfortunately, support for "Unicode (sub|super)script characters" allows an attacker to bypass this limit. Each sub/superscript group instantiated a separate Parser with its own limit on macro executions, without inheriting the current count of macro executions from its parent. This has been corrected in KaTeX v0.16.10.
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Analysis
by VulDB Data Team • 09/02/2025
The vulnerability CVE-2024-28244 affects KaTeX, a popular JavaScript library used for rendering mathematical expressions on web pages. This security flaw represents a critical bypass of the library's intended protection mechanisms, specifically targeting the maxExpand parameter that developers rely on to prevent infinite recursion in macro processing. The issue stems from how KaTeX handles Unicode subscript and superscript characters, creating a scenario where attackers can circumvent the established safety limits through carefully crafted mathematical expressions.
The technical implementation of this vulnerability exploits a fundamental flaw in KaTeX's parser architecture where each sub/superscript group initializes its own independent Parser instance with its own macro execution limit. This design decision means that when processing Unicode subscript or superscript characters, each new Parser instance starts with a fresh counter rather than inheriting the macro execution count from its parent Parser. Consequently, even when developers set maxExpand to prevent stack overflow conditions, attackers can create nested structures that effectively reset or bypass these limits through Unicode character combinations, leading to near-infinite loops that consume excessive system resources.
From an operational perspective, this vulnerability poses significant risks to web applications that render user-generated mathematical content, including educational platforms, scientific publishing systems, and collaborative mathematics tools. The impact extends beyond simple resource exhaustion as it can lead to complete application unresponsiveness or denial of service conditions, making it particularly dangerous in production environments where system availability is critical. The vulnerability specifically targets the ATT&CK technique T1499.004 - Network Denial of Service, where attackers can exploit the library's parsing behavior to consume system resources through malicious input.
The flaw manifests when attackers utilize Unicode subscript and superscript characters in conjunction with KaTeX's macro definition commands such as \def or \newcommand. This combination allows them to create recursive macro structures that appear to respect the maxExpand limit but actually bypass it through the separate Parser instantiation mechanism. The vulnerability has been classified under CWE-835 as "Loop with Unreachable Exit Condition" and represents a classic case of inadequate input validation and state management in recursive parsing systems. Security researchers have documented similar patterns in other mathematical expression libraries where Unicode character handling creates unexpected execution paths that circumvent intended safety mechanisms.
Organizations using KaTeX should immediately upgrade to version 0.16.10 or later to address this vulnerability, as the fix implements proper inheritance of macro execution counts between parent and child Parser instances. Additional mitigations include implementing input validation for mathematical expressions, limiting user-generated content complexity, and monitoring for unusual resource consumption patterns. The vulnerability highlights the importance of considering Unicode character handling in security design and demonstrates how seemingly benign character encoding support can create unexpected attack vectors in parsing systems.