Detect Incus exec-output Symlink Arbitrary File Write on Host (CVE-2026-48750) in Splunk
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
SPL Detection Query
index=linux_os OR index=endpoint sourcetype IN ("linux:audit", "syslog", "auditd", "osquery:results")
| eval is_incus_parent = if(match(parent_process, "incusd|incus"), 1, 0)
| eval sensitive_path = if(match(file_path, "^/(etc|root|var/spool/cron|usr/local/bin|lib/systemd|home/[^/]+/\.ssh)"), 1, 0)
| eval exec_output_ref = if(match(command, "exec.output|exec_output"), 1, 0)
| eval symlink_activity = if(match(syscall, "symlink|symlinkat|lstat"), 1, 0)
| where (is_incus_parent=1 AND sensitive_path=1) OR (is_incus_parent=1 AND exec_output_ref=1) OR (symlink_activity=1 AND exec_output_ref=1)
| eval threat_label = "CVE-2026-48750 Incus exec-output symlink host file write"
| table _time, host, user, parent_process, process, command, file_path, syscall, threat_label
| sort - _timeDetects incusd spawning processes that write to sensitive host paths or reference exec-output, and symlink syscalls associated with exec-output paths indicative of CVE-2026-48750 exploitation.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate container management tasks by incusd writing to monitored paths during authorized operations
- Security scanning tools running under incusd context examining system directories
- Automated CI/CD pipelines using incus that touch system paths as part of sanctioned test runs
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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