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.
The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack.