LXD has arbitrary file write on host via exec-output symlink in crafted image

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.9 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Reported from https://github.com/lxc/incus/security/advisories/GHSA-48q5-w887-33wv

Summary The `record-output` parameter of the `/instances/$name/exec` endpoint stores the output of the command in the `exec-output` directory of the instance. If `exec-output` is a symlink, file named `exec_UUID.stdout` and `exec_UUID.stderr` can be written to an arbitrary location where the `.stdout` file will contain arbitrary content. This behavior can be abused for arbitrary command execution.

Details When an image is unpacked, top-level symlinks are extracted as is; allowing for `exec-output` to be placed on disk. In `instance_exec.go`, `os.Mkdir` continues of `exec-output` exists and `os.OpenFile` follows the `exec-output` symlink.

PoC Below, we place the `exec_UUID.stdout` file in `/etc/cron.d` on the host for arbitrary command execution. ``` #!/bin/sh

usage: $0 existing-imagefp set -eu basefp="${1}" die() { printf '%s' "${@}" >&2 exit 1 } command -v curl >/dev/null 2>&1 || die…

Published by the source

6 Nov 2026, 18:45 UTC

Last modified by the source

6 Nov 2026, 19:00 UTC

Source last checked

7 Nov 2026, 06:05 UTC

1. Revision 2 · amended · 7 Nov 2026

   Amended from osv record GHSA-9j25-mm2h-2f76

2. Revision 1 · created · 6 Nov 2026

   Published from ghsa record GHSA-9j25-mm2h-2f76

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# Patch Next advisory brief: GHSA-9j25-mm2h-2f76

Advisory: LXD has arbitrary file write on host via `exec-output` symlink in crafted image
IDs: GHSA-9j25-mm2h-2f76
Record: https://patchnext.com/advisories/ghsa-9j25-mm2h-2f76 (revision 2, source checked 7 Nov 2026, 06:05 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/canonical/lxd 0.0.0-20260626085134-124f90100640. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/canonical/lxd: affected < 0.0.0-20260626085134-124f90100640; fixed in 0.0.0-20260626085134-124f90100640

## Suggested inspection (read-only)
- Go github.com/canonical/lxd: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/canonical/lxd.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9j25-mm2h-2f76 (GitHub-reviewed advisory GHSA-9j25-mm2h-2f76 lists affected ranges: Go github.com/canonical/lxd >=0 <0.0.0-20260626085134-124f90100640)
- Verified: https://osv.dev/vulnerability/GHSA-9j25-mm2h-2f76 (OSV record GHSA-9j25-mm2h-2f76 lists affected ranges: Go github.com/canonical/lxd >=0 <0.0.0-20260626085134-124f90100640 (fixed))

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