Inefficient regular expression complexity in path-to-regexp - CVE-2026-4923
Published: November 9, 2026
Vulnerability identifier: #VU162701
CSH Severity: Medium
CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-4923
CWE-ID: CWE-1333
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows an unauthenticated remote attacker to cause denial of service in applications using path-to-regexp for path matching.
The vulnerability exists due to excessive regular expression backtracking in path-to-regexp when a configured path contains multiple wildcards and at least one parameter, with the second wildcard positioned before the end of the path. An unauthenticated remote attacker can submit a crafted path to trigger expensive matching and exhaust application processing resources.
Affected software
path-to-regexp
How to mitigate CVE-2026-4923
Install security update from vendor's website.
path-to-regexp - update to 8.4.0