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.

Affected: npm: katex

### Impact 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. This can be used as an availability attack, where e.g. a client rendering another user's KaTeX input will be unable to use the site due to memory overflow, tying up the main thread, or stack overflow.

### Patches Upgrade to KaTeX v0.16.10 to remove this vulnerability.

### Workarounds Forbid inputs containing any of the characters `₊₋₌₍₎₀₁₂₃₄₅₆₇₈₉ₐₑₕᵢⱼₖₗₘₙₒₚᵣₛₜᵤᵥₓᵦᵧᵨᵩᵪ⁺⁻⁼⁽⁾⁰¹²³⁴⁵⁶⁷⁸⁹ᵃᵇᶜᵈᵉᵍʰⁱʲᵏˡᵐⁿᵒᵖʳˢᵗᵘʷˣʸᶻᵛᵝᵞᵟᵠᵡ` before passing them to KaTeX. (There is no easy workaround for the auto-render extension.)

### Details 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"](https://github.com/KaTeX/KaTeX/commit/d8fc35e6a97f8e561c723b93ad275cf5a7f3094a) 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.

### For more information If you have any questions or comments about this advisory: * Open an issue or security advisory in the [KaTeX repository](https://github.com/KaTeX/KaTeX/) * Email…

Withdrawn by the publisher.

Affected: Ubuntu:24.04:LTS: node-katex, Ubuntu:25.04: node-katex

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.