Path-to-regexp is a utility for converting Express-style path strings into regular expressions, useful for routing and pattern matching in JavaScript applications. Comparing versions 2.1.0 and 2.2.0 of this package exposes minor but potentially relevant changes for developers. Both versions share the same core description and development dependencies, including testing frameworks like Chai and Mocha, along with TypeScript support through ts-node and type definitions. The license remains MIT, and the repository URL is consistent, indicating no fundamental shift in project ownership or licensing.
The primary difference lies in the dist section and the release date. Version 2.2.0, released on March 7, 2018, specifies fileCount as 6 and unpackedSize as 26717, suggesting some code modification, added files, or optimization leading to changes in the overall size of the package. Version 2.1.0 was released earlier, on October 20, 2017, and lacks these specific size details within the metadata.
For developers, upgrading to version 2.2.0 might be desirable due to potential bug fixes, performance improvements, or minor feature enhancements that justified the new release. The increased unpackedSize implies possible additions, which may offer extended functionality. However, developers should thoroughly test the update to ensure compatibility with their existing codebase, particularly if they rely on specific internal behaviors of the library. Considering the unchanged dependencies, a smooth transition is likely, focusing on the core path-to-regexp logic and its impact on routing within the application.
All the vulnerabilities related to the version 2.2.0 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.
