# CVE-2026-63343: Arbitrary File Read/Write: metadata.yaml symlink in image allows host filesystem access as root

> Authenticated users can read or overwrite arbitrary host files as root via a malicious metadata.yaml symlink in an image.

- **Severity:** Critical 9.9 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 Aug 2026
- **Updated:** 21 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-63343, GHSA-fmjx-5j3g-997p, UBUNTU-CVE-2026-63343

## What is CVE-2026-63343?

CVE-2026-63343 is a critical path traversal vulnerability in lxc incus, published on 21 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Incus is a system container and virtual machine manager. Prior to version 7.3.0, a malicious image containing a `metadata.yaml` symlink pointing to an arbitrary host path allows an authenticated Incus user to read or overwrite any file on the host as root via the instance metadata API. The `exec-output` and `templates/` paths were patched in a prior release using `Lstat` rejection and `os.OpenRoot` confinement; `metadata.yaml` was not included in either patch and remains exploitable. Version 7.3.0 patches the issue.

Weakness: CWE-73 (External Control of File Name or Path)

## Which versions are affected by CVE-2026-63343?


## How do I fix CVE-2026-63343?

Upgrade to a fixed version.

## Is CVE-2026-63343 being exploited?

There is no known exploitation of CVE-2026-63343 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63343 and fix it if it is affected.

What it is: CVE-2026-63343 is a critical path traversal vulnerability in lxc incus, published on 21 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-63343 in the wild and no public exploit code.

Affected product: lxc incus. 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-2026-63343/ (Markdown: https://insights.sbomify.com/CVE-2026-63343/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63343
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63343
- OSV: https://osv.dev/vulnerability/CVE-2026-63343

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63343/
Summaries are generated and may contain mistakes; the official description above is the record.