Detect CVE-2026-48753: Incus S3 Multipart Upload Path Traversal Arbitrary File Write in Sumo Logic CSE
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
Sumo Detection Query
_sourceCategory=linux/syslog OR _sourceCategory=endpoint/file_events OR _sourceCategory=audit/auditd
| where _sourceCategory matches "*incus*" or process_name matches "incusd"
| parse field=message "*" as raw_message nodrop
| if(raw_message matches "*../*" or raw_message matches "*%2e%2e%2f*" or raw_message matches "*%2e%2e/*" or raw_message matches "*%252e%252e*", true, false) as has_traversal
| if(_sourceCategory = "endpoint/file_events" and !(file_path matches "/var/lib/incus/*" or file_path matches "/run/incus/*"), true, false) as file_outside_incus
| where has_traversal or file_outside_incus
| eval risk = if(has_traversal and file_outside_incus, "CRITICAL", if(has_traversal, "HIGH", "MEDIUM"))
| count by _sourceHost, process_name, risk, has_traversal, file_outside_incus
| where _count > 0
| order by risk, _count descSumo Logic query detecting CVE-2026-48753 exploitation patterns including path traversal sequences in Incus daemon messages and anomalous file write activity outside standard Incus directories.
Data Sources
False Positives & Tuning
- Authorized Incus storage pool migrations using non-default paths during maintenance windows
- Penetration testing activities against Incus S3 endpoint with explicit authorization
- Custom Incus configurations storing data outside the default /var/lib/incus directory structure
- Log parsers or SIEM forwarding agents processing Incus data from alternate locations
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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