Path-to-regexp saw a significant update between version 6.1.0 and 6.2.0, impacting the developer experience primarily through dependency upgrades. Several key development dependencies were bumped, reflecting a move towards newer tooling. Most notably, Jest was upgraded from version 24.9.0 to 26.2.2, TypeScript jumped from 3.7.2 to 4.0.3, and Node.js type definitions moved from version 12 to version 14. These changes suggest that the development team has modernized their development workflow, potentially leveraging newer features and optimizations offered by these tools. Other notable updates include husky, rimraf, prettier, size-limit, and tslint.
From a consumer perspective, while the core functionality of the library remains consistent (parsing Express-style paths into regular expressions), the update to newer versions of typescript and its related tooling should provide an improved developer experience in Typescript-based projects.
The package size has also been dramatically reduced. Version 6.1.0 had an unpacked size of approximately 476KB with 14 files, whereas version 6.2.0 has been reduced to 111KB with 9 files. This reduction hints at potential optimizations in the build process and a leaner package for distribution which improves the bundle size for your websites. The upgrade signifies a commitment to modern development practices and improved performance, making path-to-regexp a more robust and efficient choice for routing needs. Finally, it is worth noting the 6.2.0 has a newer release date.
All the vulnerabilities related to the version 6.2.0 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.
