Path-to-regexp is a small, yet powerful, utility for converting Express-style path strings into regular expressions. Used for route matching in applications, this tool provides a straightforward way to define flexible and dynamic paths. Examining versions 0.1.1 and 0.1.2 reveals minimal differences, highlighting the library's stability. The primary change appears to be the shift from declaring "mocha" and "istanbul" as dependencies in version 0.1.1 to declaring them as "devDependencies" in version 0.1.2. This subtle change implies that mocha and istanbul are used for development and testing purposes, not runtime dependencies, which can reduce the final bundle size for consumers of the library. These tools focus on testing and code coverage and are not required for the package to function.
Both versions share the same core functionality: transforming path patterns like /users/:id into regular expressions capable of extracting parameters, making it ideal for routing logic in web frameworks and applications. The "releaseDate" metadata indicates both versions were published on the same day, with only a few minutes separating them, reinforcing the notion that the 0.1.2 release was likely a minor fix to the package metadata rather than a significant functional update. Developers can use path-to-regexp to define clean REST API URL patterns, create flexible navigation for single-page applications, and other scenarios requiring dynamic route matching.
All the vulnerabilities related to the version 0.1.2 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.
