Path-to-regexp version 5.0.0 introduces subtle but potentially important changes compared to its predecessor, version 4.0.5. Both versions, sharing the same MIT license and repository on Github under the pillarjs organization, serve as utilities for converting Express-style paths into regular expressions, a core function in web application routing. The primary difference lies in the dist object, where unpackedSize has slightly decreased from 471565 bytes in version 4.0.5 to 468899 bytes in version 5.0.0 suggesting potential optimizations of the code of the package. The releaseDate also differs, with version 5.0.0 being released shortly after version 4.0.5, indicating a quick iteration or patch.
For developers, this means upgrading from 4.0.5 may introduce minor improvements in terms of bundle size. However, the small difference suggests the core functionality remains the same so no breaking changes will happen. Developers should always prioritize reviewing the complete changelog and migration guide (if available) to fully understand the specific changes included in version 5.0.0 and assess any potential impact on their application before updating. The listed devDependencies remaining consistent is also a good indicator of no breaking changes since the development enviornment is consistent. Both version provide the same utility of translating routes to regular expressions, which makes path management in web apps easier.
All the vulnerabilities related to the version 5.0.0 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.
