Path-to-regexp is a popular JavaScript utility for converting Express-style path strings into regular expressions, enabling flexible and powerful route matching in web applications and other projects. Version 3.2.0 introduces several notable changes compared to version 3.1.0, potentially influencing developers using the library. A key difference lies in the development dependencies. The newer version upgrades several packages, including TypeScript (from 3.0.1 to 3.7.2) and introduces "nyc" for code coverage, suggesting an increased focus on testing and code quality. "Istanbul" which was present in the previous stable version is not present in the newer version. These updates likely contribute to improved stability and reliability of the package. Furthermore, the unpacked size of the package has grown slightly (from 28721 to 30871 bytes), indicating added features, improved code, or updated dependencies. Developers choosing between these versions should consider that v3.2.0 benefits from newer tooling and focuses on quality, potentially leading to a more robust and maintainable dependency. If your project requires the latest TypeScript features or relies on "nyc" for code coverage, v3.2.0 is the preferred choice. However, if you need a smaller dependency or require Typescript 3.0.1, v3.1.0 might be sufficient. Always ensure compatibility with other parts of your project when updating dependencies.
All the vulnerabilities related to the version 3.2.0 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.
