In short
- CVE-2026-4926 is a HIGH (CVSS 7.5) vulnerability affecting path-to-regexp (pillarjs), path-to-regexp.
- Chance of exploitation in the next 30 days (EPSS): 0.80%, higher than 56.9% of all vulnerabilities.
- Fix: update to 8.4.0 or later.
Description
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.
NVD description
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.
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