Path-to-regexp is a small, focused utility that converts Express-style path strings into Regular Expressions. This allows developers to easily match routes in their applications, a critical aspect of routing in web servers and single-page applications. Comparing version 1.2.0 and 1.2.1 of the package reveals that the update is a patch release, likely containing bug fixes and minor improvements rather than major feature additions. Both versions share the same core functionality, using the isarray dependency and development tools like Chai for testing. Developers will find that both versions offer the same foundational approach to path matching. The key difference between them appears to be the release date, with version 1.2.1 being released approximately three months after version 1.2.0.
For developers, this comparison indicates the stability and maturity of path-to-regexp. The lack of changes suggests a reliable core with each version. Upgrading from 1.2.0 to 1.2.1 is likely a safe and recommended practice since patch version upgrades usually include essential bug fixes. When selecting which version to use, developers will want to choose the latest available. The presence of development dependencies like Mocha, Istanbul, and Standard showcases the project's commitment to quality through testing, code coverage analysis, and code style consistency.
All the vulnerabilities related to the version 1.2.1 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.
