KaTeX's maxExpand bypassed by Unicode sub/superscripts

Vulnerability Description

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.

References

• https://github.com/KaTeX/KaTeX/security/advisories/GHSA-cvr6-37gx-v8wc
• https://github.com/KaTeX/KaTeX/commit/085e21b5da05414efefa932570e7201a7c70e5b2