CVE-2026-4867

Description

### Impact A bad regular expression is generated any time you have three or more parameters within a single segment, separated by something that is not a period (`.`). For example, `/:a-:b-:c` or `/:a-:b-:c-:d`. The backtrack protection added in `[email protected]` only prevents ambiguity for two parameters. With three or more, the generated lookahead does not block single separator characters, so capture groups overlap and cause catastrophic backtracking. ### Patches Upgrade to [[email protected]](https://github.com/pillarjs/path-to-regexp/releases/tag/v.0.1.13) Custom regex patterns in route definitions (e.g., `/:a-:b([^-/]+)-:c([^-/]+)`) are not affected because they override the default capture group. ### Workarounds 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-:c` to `/:a-:b([^-/]+)-:c([^-/]+)`. If paths cannot be rewritten and versions cannot be upgraded, another alternative is to limit the URL length. ### References - [GHSA-9wv6-86v2-598j](https://github.com/advisories/GHSA-9wv6-86v2-598j) - [Detailed blog post: ReDoS the web](https://blakeembrey.com/posts/2024-09-web-redos/)

Affected packages (2)

• Debian/node-path-to-regexpfrom 0, < 1.0.1-1
• npm/path-to-regexpfrom 0, < 0.1.13

CVSS scores

References (8)

• ADVISORYhttps://github.com/advisories/GHSA-9wv6-86v2-598j
• ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2026-4867
• ADVISORYhttps://security-tracker.debian.org/tracker/CVE-2026-4867
• PATCHhttps://github.com/pillarjs/path-to-regexp
• WEBhttps://blakeembrey.com/posts/2024-09-web-redos
• WEBhttps://cna.openjsf.org/security-advisories.html
• WEBhttps://github.com/pillarjs/path-to-regexp/releases/tag/v.0.1.13
• WEBhttps://github.com/pillarjs/path-to-regexp/security/advisories/GHSA-37ch-88jc-xwx2