Detect CVE-2026-48749: Incus Arbitrary File Read/Write via rootfs Symlink in Malicious Image in Sumo Logic CSE
Detects exploitation of CVE-2026-48749, a critical vulnerability in Incus (github.com/lxc/incus/v7/cmd/incusd) versions prior to 7.2.0. Attackers can craft a malicious container image with symlinks in the rootfs/ directory that resolve to host filesystem paths, enabling arbitrary file read and write on the underlying host. This constitutes a container escape primitive and may lead to full host compromise. CVSS 9.9 with public PoC available.
MITRE ATT&CK
Sumo Detection Query
_sourceCategory=linux/audit OR _sourceCategory=linux/syslog
| parse regex "(?<process>incusd|incus)" nodrop
| parse regex "(?<file_path>/(?:var/lib/incus|etc/passwd|etc/shadow|root/\.ssh|etc/sudoers|etc/crontab)[^\s\"']*)"
| parse regex "(?<syscall>symlink|symlinkat|open|openat|creat)" nodrop
| where !isNull(process) AND !isNull(file_path)
| eval is_rootfs = if(file_path matches "/var/lib/incus/*/rootfs/*", "yes", "no")
| eval is_host_sensitive = if(
file_path matches "/etc/passwd" OR
file_path matches "/etc/shadow" OR
file_path matches "/root/.ssh/*" OR
file_path matches "/etc/sudoers*",
"yes", "no"
)
| eval alert_priority = if(is_rootfs="yes" AND is_host_sensitive="yes", "CRITICAL",
if(is_rootfs="yes" OR is_host_sensitive="yes", "HIGH", "MEDIUM"))
| where alert_priority in ("CRITICAL", "HIGH")
| stats count AS events, values(file_path) AS accessed_paths, first(alert_priority) AS priority by _sourceHost, process, alert_priority
| sort by priority, events descSumo Logic detection parsing Linux audit and syslog sources for incusd interactions with Incus rootfs symlink paths and sensitive host files, flagging CVE-2026-48749 exploitation attempts.
Data Sources
Required Tables
False Positives & Tuning
- Routine Incus container lifecycle operations that access rootfs during start/stop sequences
- Image export operations that traverse rootfs symlinks legitimately during packaging
- Host-level monitoring agents that inspect container directories for compliance checks
- Incus cluster synchronization processes accessing shared storage paths
Other platforms for CVE-2026-48749
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 Incus image with rootfs symlink targeting /etc/passwd
Expected signal: auditd syscall events for symlink() within /var/lib/incus/*/rootfs/; file open events on host /etc/passwd initiated by incusd process; DeviceFileEvents showing incusd accessing /etc/passwd outside container namespace
- Test 2Exploit rootfs symlink for host SSH authorized_keys write
Expected signal: File write event on host /root/.ssh/authorized_keys attributed to incusd or container init process; auditd records showing write() syscall to /root/.ssh/authorized_keys from incusd context; FIM alert on /root/.ssh/authorized_keys modification
- Test 3Read host /etc/shadow via rootfs symlink for credential harvesting
Expected signal: File read event on host /etc/shadow initiated by incusd process context; auditd openat() syscall on /etc/shadow attributed to container namespace but resolved to host inode; audit log entry for privileged file access outside expected paths
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