# CVE-2026-4867

## Summary

- **CVE ID:** CVE-2026-4867
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** CWE-1333
- **Published:** Mar 26, 2026
- **Last Modified:** Mar 26, 2026

## Description

Impact:

A bad regular expression is generated any time you have three or more parameters within a single segment, separated by something that is not a period (.). For example, /:a-:b-:c or /:a-:b-:c-:d. The backtrack protection added in path-to-regexp@0.1.12 only prevents ambiguity for two parameters. With three or more, the generated lookahead does not block single separator characters, so capture groups overlap and cause catastrophic backtracking.

Patches:

Upgrade to path-to-regexp@0.1.13

Custom regex patterns in route definitions (e.g., /:a-:b([^-/]+)-:c([^-/]+)) are not affected because they override the default capture group.

Workarounds:

All versions can be patched by providing a custom regular expression for parameters after the first in a single segment. As long as the custom regular expression does not match the text before the parameter, you will be safe. For example, change /:a-:b-:c to /:a-:b([^-/]+)-:c([^-/]+).

If paths cannot be rewritten and versions cannot be upgraded, another alternative is to limit the URL length.

## Affected Products

- path-to-regexp — path-to-regexp (0)

## References

- [CNA](https://cna.openjsf.org/security-advisories.html)
- [CNA](https://github.com/advisories/GHSA-9wv6-86v2-598j)
- [CNA](https://blakeembrey.com/posts/2024-09-web-redos)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.50%
- **EPSS Percentile:** 41.0

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._