Detect Incus exec-output Symlink Arbitrary File Write on Host (CVE-2026-48750) in Elastic Security
CVE-2026-48750 is a critical arbitrary file write vulnerability (CVSS 9.9) in Incus container/VM manager (github.com/lxc/incus/v7/cmd/incusd) versions prior to 7.2.0. A crafted container image can place a symlink at the exec-output path, causing incusd to write attacker-controlled content to arbitrary locations on the host filesystem. This enables container escape leading to full host compromise. A public PoC is available.
MITRE ATT&CK
Elastic Detection Query
sequence by host.name with maxspan=5m
[process where process.parent.name in ("incusd", "incus") and
process.name in ("ln", "cp", "mv", "bash", "sh", "tee", "install") and
process.command_line : ("*exec*output*", "*exec_output*", "*/var/log/incus*", "*/run/incus*")]
[file where process.parent.name in ("incusd", "incus") and
file.path : ("/etc/*", "/root/*", "/var/spool/cron/*", "/usr/local/bin/*", "/lib/systemd/*", "/home/*/.ssh/*") and
event.action in ("creation", "overwrite")]EQL sequence detecting incusd spawning a process referencing exec-output followed by a file write to a sensitive host path within 5 minutes, indicating possible CVE-2026-48750 exploitation chain.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate incus administration creating files in monitored locations as part of authorized maintenance
- Container image build pipelines that invoke exec-output and write artifacts to system paths in controlled environments
- Monitoring agents running under incusd that read and copy system files for telemetry
Other platforms for CVE-2026-48750
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Create malicious symlink in exec-output path within container image
Expected signal: Auditd symlink syscall from process tree rooted at incusd; file write event to /etc/passwd path originating from incusd child process
- Test 2Detect symlink traversal via exec-output to /root/.ssh/authorized_keys
Expected signal: File write syscall to /root/.ssh/authorized_keys with incusd ancestor in process tree; auditd type=PATH record for authorized_keys
- Test 3Simulate exec-output symlink to systemd service unit for persistence
Expected signal: File creation event under /lib/systemd/system/ with incusd ancestor; subsequent systemd daemon-reload or service enable events
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