Path-to-regexp is a small utility designed to convert Express-style path strings into regular expressions. Examining versions 1.3.0 and 1.2.1 reveals incremental improvements and updates for developers. Both versions share the same core functionality of transforming route paths into regular expressions, a common need in web application development and routing logic. Both versions depend on isarray and share the same license (MIT) and repository, ensuring stability and a permissive license for various uses.
Significant enhancements appear in the development dependencies of version 1.3.0. Specifically, ts-node, typings, and typescript are added. This suggests a move towards incorporating TypeScript for development, likely improving code maintainability, type safety, and enabling enhanced tooling for contributors. The inclusion of typings implies a focus on providing type definitions, a crucial benefit for TypeScript users who want to leverage the library with strong typing. These additions signal a commitment to modern development practices. The release data also indicates that version 1.3.0 was released significantly later than 1.2.1, suggesting a period of enhancements and bug fixing occurred between the releases. Developers using TypeScript should particularly prioritize version 1.3.0 due to its enhanced support. If not using Typescript, the differences are less important, and the upgrade value comes mainly from possible bug fixes and minor improvements.
All the vulnerabilities related to the version 1.3.0 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.
