VulnerabilityModified

CVE-2026-4926

The generated regex grows exponentially with the number of groups, causing denial of service.

HIGH 7.5EPSS 0.80%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (0.80%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

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.

CVSS 3.1: 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS: 0.80% probability · 57th percentile
Public exploits: None in Exploit-DB
CISA KEV: Not listed
Weakness: CWE-400, CWE-1333
Affected: pillarjs/path-to-regexp
Source: ce714d77-add3-4f53-aff5-83d477b104bb

EPSS trend

EPSS 0.8% since 27 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.