Path-to-regexp, a utility for converting Express-style paths into regular expressions, saw a version bump from 6.2.0 to 6.2.1, introducing some notable changes primarily in the development dependencies. Developers considering an upgrade should note these shifts. Version 6.2.1 reflects an update to more modern tooling, evidenced by the replacements in devDependencies. Notably, jest, husky, rimraf, tslint, ts-jest, prettier, lint-staged, tslint-config-prettier, and tslint-config-standard present in 6.2.0 have been removed. These are replaced by @borderless/ts-scripts, signifying a potential shift towards a more streamlined and consolidated build process.
Furthermore, version 6.2.1 includes upgrades to existing dependencies, for example, moving to newer versions of semver, size-limit, typescript, @types/jest, @types/node, and @size-limit/preset-small-lib. These dependency updates might include bug fixes, performance improvements, and compatibility with newer environments. While the core functionality of path-to-regexp likely remains consistent between the two versions, developers adopting 6.2.1 will benefit from a more contemporary development environment and potentially smaller bundle sizes due to updated size-limit. The unpacked size also decreased slighly. The move also means using newer versions of Typescript and Node.js, and it makes the overall toolchain easier to maintain and use, trading potentially some manual configuration for an opinionated but modern setup with @borderless/ts-scripts.
All the vulnerabilities related to the version 6.2.1 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.
