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Vulnerability record · CVE-2026-4923 · published 26 March 2026

CVE-2026-4923: Pillarjs path-to-regexp inefficient regular expression (redos) vulnerability

PPillarjs · Path To Regexp

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.

5.9 CVSS 3.1 Medium EPSS 0.37% · top 71.6% CWE-1333 · Inefficient regular expression (ReDoS)
5.9CVSS 3.1 base score
0.37%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
1References
17 Jun 2026Last modified by NVD

Description

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.

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://cna.openjsf.org/security-advisories.html Third Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

7.5CVE-2026-4926Pillarjs path-to-regexp uncontrolled resource consumption vulnerabilityImpact: A bad regular expression is generated any time you have multiple sequential optional groups (curly brace syntax), such as `{a}{b}{c}:z`. The …EPSS 0.89%7.5CVE-2026-4867Pillarjs path-to-regexp inefficient regular expression (redos) vulnerabilityImpact: A bad regular expression is generated any time you have three or more parameters within a single segment, separated by something that is not …EPSS 0.62%

Source: NIST National Vulnerability Database (record CVE-2026-4923), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.