Path-to-regexp is a lightweight utility for converting Express-style path strings into regular expressions. It provides a simple way to match routes and extract parameters from URLs, vital for routing logic in web applications and servers. Focusing on versions 0.1.2 and 0.1.3, the core functionality remains the same: developers can define routes using patterns like /users/:id and easily generate regular expressions to match these patterns against actual URL paths. The primary difference lies in the timing of the releases. Version 0.1.2 was released on March 10, 2014, while version 0.1.3 came out on July 6, 2014.
While both versions share the same dependencies(mocha and istanbul are listed as devDependencies), suggesting a focus on testing and code coverage, the later release hints at potential bug fixes, performance improvements, or minor feature enhancements that are however not explicitly documented in the metadata. Developers already using version 0.1.2 and encountering issues or seeking better performance might find upgrading to 0.1.3 beneficial. For new users,opting for the newer version 0.1.3 is advisable as it incorporates any improvements made since the earlier release, ensuring a more stable and reliable experience with the path-to-regexp library.
All the vulnerabilities related to the version 0.1.3 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.
path-to-regexp contains a ReDoS
The regular expression that is vulnerable to backtracking can be generated in versions before 0.1.12 of path-to-regexp, originally reported in CVE-2024-45296
Upgrade to 0.1.12.
Avoid using two parameters within a single path segment, when the separator is not . (e.g. no /:a-:b). Alternatively, you can define the regex used for both parameters and ensure they do not overlap to allow backtracking.
