Detect CVE-2026-48753: Incus S3 Multipart Upload Path Traversal Arbitrary File Write in CrowdStrike LogScale
Detects exploitation of CVE-2026-48753, a critical path traversal vulnerability (CVSS 9.9) in Incus (github.com/lxc/incus/v7/cmd/incusd) versions prior to 7.1.0. An attacker can write arbitrary files on the host by crafting malicious S3 multipart upload requests containing path traversal sequences in the object key, potentially leading to container escape, privilege escalation, or persistent backdoor installation.
MITRE ATT&CK
LogScale Detection Query
#repo=base_sensor_events #category=FileWrittenEvent
| filter (ImageFileName=/\/incusd$/ OR ParentBaseFileName="incusd")
| filter NOT (
TargetFileName STARTS WITH "/var/lib/incus/storage-pools/" OR
TargetFileName STARTS WITH "/var/lib/incus/containers/" OR
TargetFileName STARTS WITH "/run/incus/" OR
TargetFileName STARTS WITH "/tmp/incus"
)
| eval risk_indicator = "file_write_outside_incus_storage"
| join type=left
(
#repo=base_sensor_events #category=NetworkConnectIP4
| filter ImageFileName=/\/incusd$/
| filter RemotePort IN (443, 9000, 9001, 8080)
| eval risk_indicator = "s3_network_connection"
| fields ProcessStartTime, aid, ContextProcessId, RemoteIP, RemotePort
)
aid, ContextProcessId
| stats count() AS event_count, values(TargetFileName) AS affected_files,
values(RemoteIP) AS remote_ips, values(RemotePort) AS remote_ports
by aid, UserName, ImageFileName, bin(timestamp, 5m)
| where event_count > 0
| sort -event_countCrowdStrike CQL detection joining Incus file write events outside expected storage paths with S3 network connections from the same process, providing high-fidelity detection of CVE-2026-48753 exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Incus backup agents writing snapshots to alternative storage paths configured by administrators
- Custom CrowdStrike exclusions for Incus hosts may suppress legitimate file write telemetry
- Incus storage pool expansion operations temporarily writing to paths not yet indexed by the sensor
- Multi-tenant Incus deployments using non-standard directory hierarchies for tenant isolation
Other platforms for CVE-2026-48753
Testing Methodology
Validate this detection against 4 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 1CVE-2026-48753 PoC: Path Traversal via S3 Multipart Upload Initiation
Expected signal: Network log showing PUT/POST request to Incus S3 endpoint with URL-encoded path traversal sequence in the request URI; incusd process log entries showing the malformed object key
- Test 2CVE-2026-48753 Simulation: Anomalous File Write by Incusd Process
Expected signal: Linux audit log (auditd) syscall record showing openat/write to /etc/cron.d/ by process running as root; osquery file_events showing new file creation at sensitive path; EDR file creation alert for /etc/cron.d/
- Test 3CVE-2026-48753 Detection Validation: Incusd Version Audit
Expected signal: Process execution telemetry showing incus binary invoked with --version flag; no file modifications or network connections generated
- Test 4CVE-2026-48753 S3 Multipart Upload with Double-Encoded Traversal
Expected signal: Network request logs showing PUT to Incus S3 endpoint with %252e%252e and %2e%2e encoded sequences; incusd application logs recording the object key with encoded traversal characters before server-side decoding
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