Path-to-Regexp is a utility for converting path strings, commonly used in routing, into regular expressions, heavily inspired by Express's routing mechanism. Version 1.5.3 and 1.5.2 share nearly identical characteristics, both offering the core functionality of translating route paths into regular expressions suitable for matching URLs. The minimal difference between these versions lies primarily in their release dates. Version 1.5.3 was released on June 16, 2016, slightly after version 1.5.2, released on the same day.
Both versions depend on the isarray package for array checking and include an identical set of development dependencies crucial for testing and code quality, such as Chai for assertions, Mocha for testing framework, ts-node for executing TypeScript code, Typings for managing TypeScript definition files, Istanbul for code coverage, Standard for code style enforcement, and TypeScript for static typing. Developers migrating from 1.5.2 to 1.5.3 should experience no breaking changes given the similarities. The MIT license ensures open usage and modification, and the repository remains consistent for both versions, indicating a stable and maintained project. The relevant factor for developers interested in integrating Path-to-Regexp is its core function for streamlined URL parsing and matching within routing implementations.
All the vulnerabilities related to the version 1.5.3 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.
