Path-to-regexp is a tiny, yet powerful utility for converting Express-style route paths into regular expressions, crucial for routing and matching URLs in web applications. Comparing versions 2.2.1 and 2.2.0 reveals subtle but potentially important changes for developers. Both versions share an identical set of development dependencies, including tools for testing (Chai, Mocha), TypeScript support (ts-node, typescript, @types/chai, @types/node, @types/mocha), code coverage (istanbul), and code style enforcement (standard). This indicates a consistent development and testing process across both releases, ensuring quality and reliability. They are licensed under MIT.
While the core functionality remains the same, the most visible difference lies in the dist object. Version 2.2.1 has a slightly larger unpacked size of 26739 bytes compared to version 2.2.0's 26717 bytes. This suggests minor code adjustments, potentially bug fixes, or optimizations within the library. The release dates further highlight this, with version 2.2.1 being released on April 24, 2018, after version 2.2.0's release on March 7, 2018. For developers, upgrading from 2.2.0 to 2.2.1 is advisable to benefit from any bug fixes or performance improvements, even if they are not explicitly documented. The consistent development dependencies and MIT license provide assurance of continued maintenance and ease of integration into various projects.
All the vulnerabilities related to the version 2.2.1 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.
