Malicious SesameOp Netapi64 Artifact Files Written to Windows Temp (via file_event)

ATT&CK techniques

Priv Esc → Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
- T1055Process Injection
Defense Evasion
- T1055Process Injection
- T1140Deobfuscate/Decode Files or Information
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule detects creation of SesameOp working files such as Netapi64.start and Netapi64.Exception in Windows Temp along with files carrying the .Netapi64 extension. These artifacts are dropped by the SesameOp backdoor while it decrypts payloads and stores state for its OpenAI Assistants API C2 relay. Surfacing these distinctive on-disk markers reveals an active backdoor foothold that hides its traffic inside a legitimate cloud API.

Reporting behind it

Related detections9 linkedT1140 — drag to rearrange

Suspicious Base64 Decoded Payload Piped to Shell on Linux

Suspicious Remote File Download via certutil URLCache (via process_creation)

Suspicious PowerShell Shellcode Loader via Function Pointer Delegate

Malicious certutil Decodehex Payload Reconstruction by DarkGate

Suspicious StrelaStealer Base64 Payload Decode via Certutil (via process_creation)

Suspicious Named Pipe Created by Kazuar Backdoor for Interprocess Command Channel

Suspicious File Download via certutil URLCache (via process_creation)

Suspicious Base64 Decoding Piped to Shell on macOS

Suspicious Hex Decoding Piped to Shell via xxd on macOS

Malicious SesameOp Netapi64 Artifact Files Written to Windows Temp (via file_event)

Pivot detection · T1140 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

Full detection rule

Unlock this rule to view and copy it

The detection logic is included with a plan. Everything else — context, mappings and implementation details — stays free on this page.

Sign in for 3 free unlocks

Signing in gives you 3 unlocks to spend on any rule in the library. No card, and they do not expire.

Also included

Unlocked rules convert on this page — to Splunk SPL or Splunk — Raw Index SPL or Microsoft Sentinel KQL or Microsoft Sentinel ASIM ASIM KQL or Microsoft Defender XDR KQL or Elastic Security KQL or Elastic Security Lucene or Elastic Security ES|QL or CrowdStrike Falcon CQL or SentinelOne PowerQuery or Palo Alto Cortex XDR XQL or Carbon Black Cloud Platform Search or Carbon Black EDR Process Search or Google Security Operations UDM Search or IBM QRadar AQL or Sumo Logic Cloud SIEM Rules expression or Rapid7 InsightIDR LEQL or Graylog Search or OpenSearch Lucene or OpenSearch PPL PPL or Grafana Loki LogQL or SQLite SQL or Zircolite SQLite — with the log-source profile the engine picked, the field map it used, and everything it could not express. Converting a rule you have unlocked costs no further credit.

See it run on a free rule →Convert your own rule →