Version Details and Security Vulnerabilities

Impact

Code that uses KaTeX's trust option, specifically that provides a function to block-list certain URL protocols, can be fooled by URLs in malicious inputs that use uppercase characters in the protocol. In particular, this can allow for malicious input to generate javascript: links in the output, even if the trust function tries to forbid this protocol via trust: (context) => context.protocol !== 'javascript'.

Patches

Upgrade to KaTeX v0.16.10 to remove this vulnerability.

Workarounds

• Allow-list instead of block protocols in your trust function.
• Manually lowercase context.protocol via context.protocol.toLowerCase() before attempting to check for certain protocols.
• Avoid use of or turn off the trust option.

Details

KaTeX did not normalize the protocol entry of the context object provided to a user-specified trust-function, so it could be a mix of lowercase and/or uppercase letters.

It is generally better to allow-list by protocol, in which case this would normally not be an issue. But in some cases, you might want to block-list, and the KaTeX documentation even provides such an example:

Allow all commands but forbid specific protocol: trust: (context) => context.protocol !== 'file'

Currently KaTeX internally sees file: and File: URLs as different protocols, so context.protocol can be file or File, so the above check does not suffice. A simple workaround would be:

trust: (context) => context.protocol.toLowerCase() !== 'file'

Most URL parsers normalize the scheme to lowercase. For example, RFC3986 says:

Although schemes are case-insensitive, the canonical form is lowercase and documents that specify schemes must do so with lowercase letters. An implementation should accept uppercase letters as equivalent to lowercase in scheme names (e.g., allow "HTTP" as well as "http") for the sake of robustness but should only produce lowercase scheme names for consistency.

Impact

KaTeX users who render untrusted mathematical expressions could encounter malicious input using \edef 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 the substring "\\edef" before passing them to KaTeX. (There is no easy workaround for the auto-render extension.)

Details

KaTeX supports an option named maxExpand which prevents infinitely recursive macros from consuming all available memory and/or triggering a stack overflow error. However, what counted as an "expansion" is a single macro expanding to any number of tokens. The expand-and-define TeX command \edef can be used to build up an exponential number of tokens using only a linear number of expansions according to this definition, e.g. by repeatedly doubling the previous definition. This has been corrected in KaTeX v0.16.10, where every expanded token in an \edef counts as an expansion.

For more information

If you have any questions or comments about this advisory:

• Open an issue or security advisory in the KaTeX repository
• Email us at katex-security@mit.edu

Impact

KaTeX users who render untrusted mathematical expressions could encounter malicious input using \includegraphics that runs arbitrary JavaScript, or generate invalid HTML.

Patches

Upgrade to KaTeX v0.16.10 to remove this vulnerability.

Workarounds

• Avoid use of or turn off the trust option, or set it to forbid \includegraphics commands.
• Forbid inputs containing the substring "\\includegraphics".
• Sanitize HTML output from KaTeX.

Details

\includegraphics did not properly quote its filename argument, allowing it to generate invalid or malicious HTML that runs scripts.

For more information

If you have any questions or comments about this advisory:

• Open an issue or security advisory in the KaTeX repository
• Email us at katex-security@mit.edu

Impact

KaTeX users who render untrusted mathematical expressions with renderToString could encounter malicious input using \htmlData that runs arbitrary JavaScript, or generate invalid HTML.

Patches

Upgrade to KaTeX v0.16.21 to remove this vulnerability.

Workarounds

• Avoid use of or turn off the trust option, or set it to forbid \htmlData commands.
• Forbid inputs containing the substring "\\htmlData".
• Sanitize HTML output from KaTeX.

Details

\htmlData did not validate its attribute name argument, allowing it to generate invalid or malicious HTML that runs scripts.

For more information

If you have any questions or comments about this advisory:

• Open an issue or security advisory in the KaTeX repository
• Email us at katex-security@mit.edu

Summary

esbuild allows any websites to send any request to the development server and read the response due to default CORS settings.

Details

esbuild sets Access-Control-Allow-Origin: * header to all requests, including the SSE connection, which allows any websites to send any request to the development server and read the response.

https://github.com/evanw/esbuild/blob/df815ac27b84f8b34374c9182a93c94718f8a630/pkg/api/serve_other.go#L121 https://github.com/evanw/esbuild/blob/df815ac27b84f8b34374c9182a93c94718f8a630/pkg/api/serve_other.go#L363

Attack scenario:

1. The attacker serves a malicious web page (http://malicious.example.com).
2. The user accesses the malicious web page.
3. The attacker sends a fetch('http://127.0.0.1:8000/main.js') request by JS in that malicious web page. This request is normally blocked by same-origin policy, but that's not the case for the reasons above.
4. The attacker gets the content of http://127.0.0.1:8000/main.js.

In this scenario, I assumed that the attacker knows the URL of the bundle output file name. But the attacker can also get that information by

• Fetching /index.html: normally you have a script tag here
• Fetching /assets: it's common to have a assets directory when you have JS files and CSS files in a different directory and the directory listing feature tells the attacker the list of files
• Connecting /esbuild SSE endpoint: the SSE endpoint sends the URL path of the changed files when the file is changed (new EventSource('/esbuild').addEventListener('change', e => console.log(e.type, e.data)))
• Fetching URLs in the known file: once the attacker knows one file, the attacker can know the URLs imported from that file

The scenario above fetches the compiled content, but if the victim has the source map option enabled, the attacker can also get the non-compiled content by fetching the source map file.

PoC

1. Download reproduction.zip
2. Extract it and move to that directory
3. Run npm i
4. Run npm run watch
5. Run fetch('http://127.0.0.1:8000/app.js').then(r => r.text()).then(content => console.log(content)) in a different website's dev tools.

Impact

Users using the serve feature may get the source code stolen by malicious websites.

Impact

When using Babel to compile regular expression named capturing groups, Babel will generate a polyfill for the .replace method that has quadratic complexity on some specific replacement pattern strings (i.e. the second argument passed to .replace).

Your generated code is vulnerable if all the following conditions are true:

• You use Babel to compile regular expression named capturing groups
• You use the .replace method on a regular expression that contains named capturing groups
• Your code uses untrusted strings as the second argument of .replace

If you are using @babel/preset-env with the targets option, the transform that injects the vulnerable code is automatically enabled if:

• you use duplicated named capturing groups, and target any browser older than Chrome/Edge 126, Opera 112, Firefox 129, Safari 17.4, or Node.js 23
• you use any named capturing groups, and target any browser older than Chrome 64, Opera 71, Edge 79, Firefox 78, Safari 11.1, or Node.js 10

You can verify what transforms @babel/preset-env is using by enabling the debug option.

Patches

This problem has been fixed in @babel/helpers and @babel/runtime 7.26.10 and 8.0.0-alpha.17, please upgrade. It's likely that you do not directly depend on @babel/helpers, and instead you depend on @babel/core (which itself depends on @babel/helpers). Upgrading to @babel/core 7.26.10 is not required, but it guarantees that you are on a new enough @babel/helpers version.

Please note that just updating your Babel dependencies is not enough: you will also need to re-compile your code.

Workarounds

If you are passing user-provided strings as the second argument of .replace on regular expressions that contain named capturing groups, validate the input and make sure it does not contain the substring $< if it's then not followed by > (possibly with other characters in between).

References

This vulnerability was reported and fixed in https://github.com/babel/babel/pull/17173.

An issue was discovered in PostCSS before 8.4.31. It affects linters using PostCSS to parse external Cascading Style Sheets (CSS). There may be \r discrepancies, as demonstrated by @font-face{ font:(\r/*);} in a rule.

This vulnerability affects linters using PostCSS to parse external untrusted CSS. An attacker can prepare CSS in such a way that it will contains parts parsed by PostCSS as a CSS comment. After processing by PostCSS, it will be included in the PostCSS output in CSS nodes (rules, properties) despite being originally included in a comment.