Path-to-regexp, a utility for converting Express-style paths into regular expressions, has two recent stable versions: 6.2.1 and 6.2.2. The key difference lies in their development dependencies and release dates. Version 6.2.2, released in April 2024, features updated tooling. Specifically, it upgrades size-limit to version ^11.1.2, TypeScript to ^5.1.6, @types/node to ^20.4.9, and introduces @vitest/coverage-v8 at ^1.4.0. In contrast, version 6.2.1, released in May 2022, uses older versions of these tools like size-limit at ^7.0.8, TypeScript at ^4.5.5, and @types/node at ^17.0.17.
Developers choosing between these versions should consider their project's compatibility with these dependency updates. Modern projects may benefit from the enhanced static analysis and code coverage provided by the newer tooling in 6.2.2. The updated TypeScript version, in particular, could offer improved type checking and language features if your project utilizes TypeScript. Moreover, the slight size reduction of unpacked size from 107798 to 107717 in the newer version may suggest some internal optimizations, though the impact is minimal. For projects requiring older Node.js or TypeScript versions, version 6.2.1 remains a viable option, ensuring smoother integration. However, for new projects it's advised to use the latest version.
All the vulnerabilities related to the version 6.2.2 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.
