Detect CVE-2026-48753: Incus S3 Multipart Upload Path Traversal Arbitrary File Write in Elastic Security
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
Elastic Detection Query
sequence by host.name with maxspan=2m
[
network where process.name == "incusd"
and (
url.path like~ "*../*"
or url.path like~ "*%2e%2e%2f*"
or url.path like~ "*%2e%2e/*"
or url.query like~ "*../*"
)
and (
destination.port == 443
or destination.port == 9000
or destination.port == 9001
)
] by process.pid
[
file where process.name == "incusd"
and event.action in ("creation", "overwrite")
and not (
file.path like "/var/lib/incus/storage-pools/*"
or file.path like "/var/lib/incus/containers/*"
or file.path like "/run/incus/*"
or file.path like "/tmp/incus*"
)
] by process.pidEQL sequence rule correlating Incus S3 network requests containing path traversal sequences with subsequent file creation events outside expected Incus storage directories, using process PID correlation within a 2-minute window.
Data Sources
Required Tables
False Positives & Tuning
- Incus storage pool migration operations touching filesystem paths temporarily outside default locations
- Legitimate object keys containing encoded characters misidentified as traversal sequences
- Custom plugin or extension processes spawned by incusd writing to authorized non-default paths
- Backup agents reading Incus data and creating staging files in non-standard directories
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
Unlock Pro Content
Get the full detection package for CVE-2026-48753 including response playbook, investigation guide, and atomic red team tests.