# CVE-2026-91018: Double Free in lwIP (lightweight IP)

> A double free vulnerability in the lwIP library allows attackers to cause denial of service or execute arbitrary code on affected systems.

- **Severity:** High 8.7 (`CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Sep 2026
- **Updated:** 23 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-91018, GHSA-rmx4-24pf-8x6h, UBUNTU-CVE-2026-91018

## What is CVE-2026-91018?

CVE-2026-91018 is a high-severity use after free vulnerability in lwIP API, published on 22 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

lwIP (Lightweight IP) has a double free vulnerability, which could crash the system, cause a DoS, memory corruption, or allow code execution on the victim system.

Weakness: CWE-415 (Double Free)

## Which versions are affected by CVE-2026-91018?


## How do I fix CVE-2026-91018?

Apply the vendor's patch.

## Is CVE-2026-91018 being exploited?

There is no known exploitation of CVE-2026-91018 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-91018 and fix it if it is affected.

What it is: CVE-2026-91018 is a high-severity use after free vulnerability in lwIP API, published on 22 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-91018 in the wild and no public exploit code.

Affected product: lwIP API. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-91018/ (Markdown: https://insights.sbomify.com/CVE-2026-91018/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-91018
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-91018
- OSV: https://osv.dev/vulnerability/CVE-2026-91018

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-91018/
Summaries are generated and may contain mistakes; the official description above is the record.