Resource exhaustion in Path-To-Regexp
CVE-2026-4926
Impact: A bad regular expression is generated any time you have multiple sequential optional groups (curly brace syntax), such as `{a}{b}{c}:z`. The generated regex grows exponentially with the number of groups, causing denial of service. Patches: Fixed in version 8.4.0. Workarounds: Limit the number of sequential optional groups in route patterns. Avoid passing user-controlled input as route patterns.
Vulnerability class: DoS (Denial of Service)
EPSS: 0.008 (52.6th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/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)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Frequently asked questions
- What is CVE-2026-4926?
- CVE-2026-4926 is a high-severity vulnerability in Path-To-Regexp, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-03-26.
- How severe is CVE-2026-4926?
- High severity. CVSS v3 base score is 7.5 out of 10.