# CVE-2026-63343: Incus arbitrary file read/write via metadata.yaml symlink

Source: https://junglewise.ai/threats/cve-2026-63343-incus-arbitrary-file-read-write-via-metadata-yaml-symlink  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-21. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-63343 · Severity: critical · CVSS 9.9 · Published 2026-08-21

Incus is a system container and virtual machine manager used to run and manage isolated workloads on a host. A vulnerability in versions before 7.3.0 allows any authenticated user to read or overwrite arbitrary files on the host system as root by crafting a malicious container image with a symlink. An attacker could steal sensitive configuration files, inject backdoors into system cron jobs, or compromise critical operational files.

## Quick answers

**Is CVE-2026-63343 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-63343 being exploited in the wild.

**How severe is CVE-2026-63343?** Critical severity, with a CVSS score of 9.9, published 21 August 2026.

**Which products and versions are affected?** Incus Incus < 7.3.0.

**Is there a fix for CVE-2026-63343?** A patch was published on 2026-08-21: Version 7.3.0 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-63343 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-63343?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a path traversal via symlink in the instance metadata API. The root cause is that Incus's tar extraction uses --restrict to prevent following symlinks outside the extraction root, but does not prevent writing symlink entries themselves. The metadata.yaml file at cmd/incusd/instance_metadata.go is then accessed and written without Lstat guards or os.OpenRoot confinement that were previously applied to exec-output and templates/ paths. An authenticated user can craft an image with metadata.yaml pointing to an arbitrary host path (e.g., /etc/cron.d/backdoor), import it, create an instance, and then use PUT /1.0/instances/{name}/metadata to write YAML-formatted content as root to the symlink target, or use GET to read the target file. The vulnerability requires authentication but no special privileges or user interaction. Version 7.3.0 patches the issue.

## Affected products

- Incus Incus < 7.3.0

## Timeline

- 2026-07-30: disclosed
- 2026-08-21: patched: Version 7.3.0 released

## References

- [https://github.com/lxc/incus/security/advisories/GHSA-fmjx-5j3g-997p](https://github.com/lxc/incus/security/advisories/GHSA-fmjx-5j3g-997p)