Path-to-regexp is a compact and versatile JavaScript utility designed for converting Express-style path strings into regular expressions. This package is a valuable tool for developers building routing systems, API endpoints, or any application requiring pattern matching against URL paths. Version 1.2.0, released on May 21, 2015, builds upon the foundation laid by version 1.1.1, released just days prior on May 12, 2015. While the core functionality and dependencies (like "isarray") remain consistent between the two versions, the newer release may incorporate bug fixes, performance enhancements, or subtle adjustments to the core algorithm which are not explicitly detailed in metadata but can improve stability and reliability. Both versions share the same development dependencies, including tools like Chai for testing, Mocha for running tests, Istanbul for code coverage, Standard for code style enforcement, and pre-commit hooks to ensure code quality before committing changes. The MIT license ensures broad usability. Developers should always prioritize the latest stable version (in this case, 1.2.0) to benefit from any improvements and fixes implemented since the previous release. Always check the project's repository on GitHub for a comprehensive changelog detailing version-specific updates and contributions that went into creating the new release, allowing for a thoroughly informed upgrade decision.
All the vulnerabilities related to the version 1.2.0 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.
