# CVE-2026-4923: path-to-regexp vulnerable to Regular Expression Denial of Service via multiple wildcards

> Attackers can cause denial of service in applications using path-to-regexp by crafting URLs with multiple wildcards that trigger excessive regex backtracking.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Mar 2026
- **Updated:** 27 Mar 2026
- **Also known as:** CLEANSTART-2026-AN94003, CLEANSTART-2026-KM38577, DEBIAN-CVE-2026-4923, ECHO-1509-22ad-8ce5, GHSA-27v5-c462-wpq7, MINI-6v7v-889h-vcq9, MINI-6vf4-rvq2-23mm, MINI-735h-cx4w-4pr5, MINI-7vm9-p8vg-74wr, MINI-8fcg-w36j-43jf, MINI-c6w2-xqrm-wf28, MINI-ggxr-x3v5-chp2, MINI-mv57-qgqr-p8x8, MINI-qw4h-wm39-fx6v, MINI-qxj2-gvg7-wpjg, MINI-r77w-pg34-96g4, MINI-v52w-w34c-mp2r, ROOT-APP-NPM-CVE-2026-4923

## What is CVE-2026-4923?

CVE-2026-4923 is a medium-severity denial of service vulnerability in path-to-regexp, published on 26 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Impact:

When using multiple wildcards, combined with at least one parameter, a regular expression can be generated that is vulnerable to ReDoS. This backtracking vulnerability requires the second wildcard to be somewhere other than the end of the path.

Unsafe examples:

/*foo-*bar-:baz
/*a-:b-*c-:d
/x/*a-:b/*c/y

Safe examples:

/*foo-:bar
/*foo-:bar-*baz

Patches:

Upgrade to version 8.4.0.

Workarounds:

If you are using multiple wildcard parameters, you can check the regex output with a tool such as https://makenowjust-labs.github.io/recheck/playground/ to confirm whether a path is vulnerable.

Weakness: CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2026-4923?

2 open source packages ship an affected version, including path-to-regexp. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `path-to-regexp` | npm | From 8.0.0 | 8.4.0 |
| `path-to-regexp` | npm | From 8.0.0 | 8.4.0 |

Products: Pillarjs Path-to-Regexp.

## How do I fix CVE-2026-4923?

Upgrade path-to-regexp to 8.4.0 or later.

## Is CVE-2026-4923 being exploited?

There is no known exploitation of CVE-2026-4923 in the wild and no public exploit code.

## Other vulnerabilities in path-to-regexp

- [CVE-2026-4867](https://insights.sbomify.com/CVE-2026-4867/): path-to-regexp vulnerable to Regular Expression Denial of Service via multiple route parameters (high 7.5)
- [CVE-2026-4926](https://insights.sbomify.com/CVE-2026-4926/): path-to-regexp vulnerable to Denial of Service via sequential optional groups (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-4923 and fix it if it is affected.

What it is: CVE-2026-4923 is a medium-severity denial of service vulnerability in path-to-regexp, published on 26 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-4923 in the wild and no public exploit code.

Affected packages and fixed versions:
- path-to-regexp (npm): affected from 8.0.0; fixed in 8.4.0
- path-to-regexp (npm): affected from 8.0.0; fixed in 8.4.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-4923/ (Markdown: https://insights.sbomify.com/CVE-2026-4923/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-4923
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-4923
- OSV: https://osv.dev/vulnerability/CVE-2026-4923

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-4923/
Summaries are generated and may contain mistakes; the official description above is the record.