Path-to-regexp is a lightweight and versatile utility designed for converting Express-style path strings into regular expressions, enabling robust route matching in your JavaScript applications. Examining versions 1.0.2 and 1.0.3, we find subtle but important differences. Both share the same core functionality, leveraging the "isarray" dependency and employing "mocha" and "istanbul" for development-related tasks such as testing and code coverage respectively. They are both released under the MIT license, meaning that they are opensource and can be used for free.
While the core functionality remains consistent, the key distinction lies in the release dates. Version 1.0.2 was released in December 2014, while version 1.0.3 arrived a month later in January 2015. This suggests potential bug fixes, performance enhancements, or minor feature updates introduced in the newer version. For developers, choosing version 1.0.3 is generally advisable due to the likelihood of incorporating improvements and addressing any known issues present in its predecessor.
Both versions provide developers with a clean and efficient way to define routes using familiar Express-style syntax and translate them into regular expressions that can be used to match incoming requests. The library also uses Github as code repository. This makes path-to-regexp a valuable tool for building web applications and APIs where dynamic route handling is essential due to the need of strong route matching functionalities in web applications.
All the vulnerabilities related to the version 1.0.3 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.
