CVE-2026-4926: path-to-regexp vulnerable to Denial of Service via sequential optional groups

March 27, 2026

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.

References

cna.openjsf.org/security-advisories.html
github.com/advisories/GHSA-j3q9-mxjg-w52f
github.com/pillarjs/path-to-regexp
github.com/pillarjs/path-to-regexp/security/advisories/GHSA-j3q9-mxjg-w52f
nvd.nist.gov/vuln/detail/CVE-2026-4926

Code Behaviors & Features

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