Path-to-regexp offers a straightforward way to convert path strings, similar to those used in Express routes, into regular expressions. Examining versions 4.0.2 and 4.0.1 reveals subtle differences, but both maintain the core functionality that makes this library useful for developers involved in routing and URL parsing. Both versions share identical development dependencies, including testing frameworks like Jest and Typescript tooling, suggesting a consistent development and testing environment. The license remains MIT for both releases, ensuring broad usability in various projects. Also the repository is stable and the same between the two versions.
The key difference lies in the distribution (dist) metadata. Version 4.0.2 has a slightly larger unpacked size (470420 bytes) compared to 4.0.1 (470372 bytes). This suggests that the newer version likely contains minor bug fixes, performance improvements, or small additions, although the number of files remains the same (14). Another meaningful difference is the releaseDate, version 4.0.2 being released a few minutes after version 4.0.1, this is very useful for developers that want to monitor the correct version of the library over time. For developers already using path-to-regexp, upgrading from 4.0.1 to 4.0.2 is recommended as it likely includes stability improvements. Developers new to the library can confidently use 4.0.2, and checking the change log can give peace of mind.
All the vulnerabilities related to the version 4.0.2 of the package
path-to-regexp outputs backtracking regular expressions
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.
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:
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 can enable strict: true and get an error when the regular expression might be bad.
Version 8.0.0 removes the features that can cause a ReDoS.
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.
Using /:a-:b will produce the regular expression /^\/([^\/]+?)-([^\/]+?)\/?$/. This can be exploited by a path such as /a${'-a'.repeat(8_000)}/a. OWASP 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.
