Path-to-regexp is a small, focused JavaScript utility designed to convert Express-style route paths into regular expressions. This enables developers to easily match URL paths against predefined patterns, a crucial capability for routing in web applications and APIs. Examining versions 0.1.5 and 0.1.6, the core functionality remains consistent: both versions utilize the same approach to translating path strings (like /users/:id) into RegExp objects that can be used to validate and extract parameters from incoming requests. From a development perspective, the key difference is the release date. Version 0.1.6 was released on June 19, 2015, subsequent to version 0.1.5 that was released on May 9, 2015.
While the provided metadata offers minimal insight into functional changes between these minor versions, the presence of "mocha" and "istanbul" in devDependencies indicates a commitment to testing and code coverage and stability using existing testing frameworks. Developers can depend on this package to provide predictable and consistent route matching, with the option to leverage the libraries' parameter extraction features for building dynamic applications. The MIT license ensures flexibility in integrating path-to-regexp into various projects, both open-source and commercial. The code repository is hosted on GitHub fostering community contributions. Both versions ship with the same dependencies and same license.
All the vulnerabilities related to the version 0.1.6 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.
