CVE-2026-4926

CVE-2026-4926 is a high-severity vulnerability in Pillarjs Path-to-regexp with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-400.

Key facts

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-4926?
CVE-2026-4926 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-4926 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (52nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-4926?
CVE-2026-4926 affects Pillarjs Path-to-regexp. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-4926?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-4926 have an EU (EUVD) identifier?
Yes. CVE-2026-4926 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16324.
When was CVE-2026-4926 published?
CVE-2026-4926 was published on 2026-03-26 and last updated on 2026-06-30.

References

Affected products (1)

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