Path-to-Regexp is a utility for converting Express-style path strings into regular expressions, facilitating route matching in applications. Examining versions 1.5.0 and 1.5.1, we see subtle but important updates. Both versions share the same core functionality, dependencies (like isarray), and development dependencies used for testing and linting (including chai, mocha, standard, and typescript). This indicates stability and a consistent development process. The MIT license ensures freedom in usage.
The primary difference lies the release date. Version 1.5.1 was published on June 8, 2016, while 1.5.0 was released on May 20, 2016. This suggests that version 1.5.1 is a patch release addressing a bug or minor enhancement identified after the 1.5.0 release. Developers should upgrade to 1.5.1 for the latest fixes and improvements.
For developers considering Path-to-Regexp, its established presence and ongoing updates (however minor), coupled with comprehensive testing infrastructure, means it's a reliable library for handling URL routes. Its core purpose is focused on simplifying a complex web development task. The package's inclusion of TypeScript definitions (via typings) and TypeScript compilation tools shows a level of support of modern Javascript ecosystem.
All the vulnerabilities related to the version 1.5.1 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.
