Vulnerability in Path-To-Regexp
CVE-2026-4923
Impact: When using multiple wildcards, combined with at least one parameter, a regular expression can be generated that is vulnerable to ReDoS. This backtracking vulnerability requires the second wildcard to be somewhere other than the end of the path. Unsafe examples: /*foo-*bar-:baz /*a-:b-*c-:d /x/*a-:b/*c/y Safe examples: /*foo-:bar /*foo-:bar-*baz Patches: Upgrade to version 8.4.0. Workarounds: If you are using multiple wildcard parameters, you can check the regex output with a tool such as https://makenowjust-labs.github.io/recheck/playground/ to confirm whether a path is vulnerable.
Vulnerability class: ReDoS (Regular Expression Denial of Service)
EPSS: 0.004 (27.9th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H.
Affected products
- Path-to-regexp — versions 8.0.0, 8.4.0
- Pillarjs Path-to-regexp
Weakness classification (CWE)
References
- ce714d77-add3-4f53-aff5-83d477b104bb (Third Party Advisory)
Frequently asked questions
- What is CVE-2026-4923?
- CVE-2026-4923 is a medium-severity vulnerability in Path-To-Regexp, classified under Inefficient Regular Expression Complexity. CVSS score: 5.9/10. Published 2026-03-26.
- How severe is CVE-2026-4923?
- Medium severity. CVSS v3 base score is 5.9 out of 10.