Path-to-regexp version 2.4.0 introduces subtle enhancements over its predecessor, version 2.3.0. Both versions serve as utilities for converting Express-style paths into regular expressions, a crucial task for routing in web applications and APIs. Focusing on the core functionality, both versions equip developers with the necessary tools to define flexible and expressive route patterns. The packages share identical development dependencies, including testing frameworks like Chai and Mocha, code quality tools like Standard, and TypeScript support, ensuring consistent code quality and developer experience across versions.
The key changes reside in the dist object, specifically the unpackedSize, which increased from 26981 bytes in version 2.3.0 to 27372 bytes in version 2.4.0. This suggests that version 2.4.0 includes a few more bytes than the previous version. The other differences are the tarball URL and the release date, which changed from August 20, 2018, to August 26, 2018. This increment may stem from bug fixes, performance improvements, or potentially adding some documentation or tests rather than completely modifying the interface for the end user. For developers, this means that upgrading to version 2.4.0 is a safe bet, likely receiving a more optimized and stable version of the path-to-regexp package without any breaking changes. Because both releases are quite old, it's important to check for more recent, actively maintained versions and consider security implications before integrating them in a contemporary software project.
All the vulnerabilities related to the version 2.4.0 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.
