Vulnerability Details 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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.001
EPSS Ranking 16.3%
CVSS Severity
CVSS v3 Score 7.5
Products affected by CVE-2026-4926
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cpe:2.3:a:pillarjs:path-to-regexp:*