Package Instance

DOMPurify allows tampering by prototype pollution
It has been discovered that malicious HTML using special nesting techniques can bypass the depth checking added to DOMPurify in recent releases. It was also possible to use Prototype Pollution to weaken the depth check.

This renders dompurify unable to avoid XSS attack.

Fixed by https://github.com/cure53/DOMPurify/commit/1e520262bf4c66b5efda49e2316d6d1246ca7b21 (3.x branch) and https://github.com/cure53/DOMPurify/commit/26e1d69ca7f769f5c558619d644d90dd8bf26ebc (2.x branch).

path-to-regexp outputs backtracking regular expressions
### Impact

A bad regular expression is generated any time you have two parameters within a single segment, separated by something that is not a period (`.`). For example, `/:a-:b`.

### Patches

For users of 0.1, upgrade to `0.1.10`. All other users should upgrade to `8.0.0`.

These versions add backtrack protection when a custom regex pattern is not provided:

- [0.1.10](https://github.com/pillarjs/path-to-regexp/releases/tag/v0.1.10)
- [1.9.0](https://github.com/pillarjs/path-to-regexp/releases/tag/v1.9.0)
- [3.3.0](https://github.com/pillarjs/path-to-regexp/releases/tag/v3.3.0)
- [6.3.0](https://github.com/pillarjs/path-to-regexp/releases/tag/v6.3.0)

They do not protect against vulnerable user supplied capture groups. Protecting against explicit user patterns is out of scope for old versions and not considered a vulnerability.

Version [7.1.0](https://github.com/pillarjs/path-to-regexp/releases/tag/v7.1.0) can enable `strict: true` and get an error when the regular expression might be bad.

Version [8.0.0](https://github.com/pillarjs/path-to-regexp/releases/tag/v8.0.0) removes the features that can cause a ReDoS.

### Workarounds

All versions can be patched by providing a custom regular expression for parameters after the first in a single segment. As long as the custom regular expression does not match the text before the parameter, you will be safe. For example, change `/:a-:b` to `/:a-:b([^-/]+)`.

If paths cannot be rewritten and versions cannot be upgraded, another alternative is to limit the URL length. For example, halving the attack string improves performance by 4x faster.

### Details

Using `/:a-:b` will produce the regular expression `/^\/([^\/]+?)-([^\/]+?)\/?$/`. This can be exploited by a path such as `/a${'-a'.repeat(8_000)}/a`. [OWASP](https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS) has a good example of why this occurs, but the TL;DR is the `/a` at the end ensures this route would never match but due to naive backtracking it will still attempt every combination of the `:a-:b` on the repeated 8,000 `-a`.

Because JavaScript is single threaded and regex matching runs on the main thread, poor performance will block the event loop and can lead to a DoS. In local benchmarks, exploiting the unsafe regex will result in performance that is over 1000x worse than the safe regex. In a more realistic environment using Express v4 and 10 concurrent connections, this translated to average latency of ~600ms vs 1ms.

### References

* [OWASP](https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS)
* [Detailed blog post](https://blakeembrey.com/posts/2024-09-web-redos/)