Path-to-regexp is a small utility that translates Express-style path strings into regular expressions, allowing developers to easily match routes. Comparing versions 2.1.0 and 2.0.0, we see primarily a timing update, with version 2.1.0 released on October 20, 2017, succeeding version 2.0.0 released on August 23, 2017. The core functionality and development dependencies like Chai, Mocha, TypeScript, and Standard remain consistent across both versions, suggesting a maintenance release rather than a major overhaul.
For developers, path-to-regexp provides a simple yet powerful way to define routes in their applications. Its compatibility with Express's familiar syntax means a shallow learning curve for those already using the framework. The library enables developers to define parameters within their paths, which can then be extracted when a match occurs. Crucially, path-to-regexp gives developers fine-grained control over route matching, accommodating complex routing needs, by allowing regular expressions parameters. Despite the minor version bump between 2.0.0 and 2.1.0, developers should check the changelog (available on the project's GitHub repository) for any specific bug fixes or minor behavioral changes that could impact their applications, ensuring a smooth upgrade path for their code. The MIT license ensures flexibility in how the library is used and integrated into different projects.
All the vulnerabilities related to the version 2.1.0 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.
