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

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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.

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