Path-to-regexp is a utility for converting Express-style path strings into regular expressions, useful for route matching in web applications and other scenarios where dynamic path handling is required. Examining versions 3.1.0 and 3.0.0 reveals subtle but potentially impactful changes. Both versions maintain the same core description and MIT license, indicating a commitment to open-source principles. The primary difference lies in the development dependencies, showcasing updates to the testing and linting toolchain. Version 3.1.0 upgrades mocha from 5.2.0 to 6.2.0, ts-node from 7.0.1 to 8.3.0, and standard from 12.0.1 to 14.1.0. @types/node also sees a jump from version 10.7.1 to 12.7.3.
These upgrades suggest improvements in testing capabilities, enhanced TypeScript support, and adherence to more modern JavaScript coding standards. While the core functionality likely remains the same, developers upgrading to 3.1.0 benefit from a more robust development environment leading to potential performance improvements or new TypeScript features. The dist information provides insights into the package size; version 3.1.0 has a slightly larger unpacked size (28721 bytes) compared to version 3.0.0 (27504 bytes), possibly due to the updated dependencies. Developers should consider these updated dependencies for potential benefits and any compatibility considerations within their existing projects. The release date difference also signifies a significant period of refinement and maintenance between the versions.
All the vulnerabilities related to the version 3.1.0 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.
