Path-to-regexp is a popular utility for converting Express-style path strings into regular expressions, widely used in routing libraries and frameworks. Version 6.1.0 represents a minor update over the previous stable version, 6.0.0, both maintained under the MIT license and accessible through the official GitHub repository. Examining the package.json data, the core functionality and intended use remain the same. Both versions share identical development dependencies, including testing frameworks like Jest and TypeScript-related tooling like tslint and @types/node, suggesting a consistent development and testing process.
The key difference lies within the dist object. Version 6.1.0 has an unpackedSize of 476190 bytes compared to 468051 bytes for version 6.0.0, indicating a slight increase in the package size. The fileCount remains constant at 14. While the increase is relatively small, this might reflect minor code changes, updated dependencies, or modifications to build artifacts improving performance. Furthermore, the releaseDate of version 6.1.0 is later (November 20, 2019) than version 6.0.0 (also November 20, 2019), showing it was released approximately 15 hours later. Developers looking to integrate path-to-regexp into their projects should consider these minor differences when choosing between the two versions. Although, functionally, they will behave similarly. Version 6.1.0 is recommended due to bugfixes or performance improvements in its later release. The library is robust and well-tested.
All the vulnerabilities related to the version 6.1.0 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.
