Malicious .cmd Email Attachment Escalates Privileges, Bypasses AV, and Deploys Payload

Malicious .cmd Email Attachment Escalates Privileges, Bypasses AV, and Deploys Payload

What Happened — A phishing email delivered a disguised .cmd script that checks for admin rights, elevates itself, creates a hidden folder, adds the folder to Windows Defender exclusions, downloads a payload disguised as a JPEG, extracts a malicious executable, and then self‑deletes.

Why It Matters for TPRM —

• Email‑borne scripts can bypass traditional AV, exposing any downstream vendor or partner that trusts the same mailbox.
• The technique uses legitimate Windows tools (PowerShell, curl, tar) making detection harder for third‑party security controls.
• Persistence is achieved via Defender exclusions, a tactic that can be replicated across any organization that allows user‑level software installation.

Who Is Affected — All industries that rely on Windows endpoints and allow email attachments, especially those with limited endpoint hardening (e.g., finance, healthcare, SaaS providers, MSPs).

Recommended Actions

• Enforce strict attachment filtering and block .cmd/.bat files at the gateway.
• Require PowerShell Constrained Language Mode or Application Control (AppLocker/WDAC) to prevent unauthorized script execution.
• Audit and monitor Windows Defender exclusion changes; alert on additions from non‑admin processes.
• Conduct phishing awareness training focused on “unexpected script attachments.”

Technical Notes —

• Attack Vector: Phishing email → .cmd script → PowerShell elevation → Windows Defender exclusion → curl download → disguised JPEG → ZIP extraction → malicious executable.
• Key Behaviors: Privilege escalation, AV bypass via exclusion, multi‑stage payload delivery, self‑deletion.
• Indicators: hxxps://search[.]app/a3qBe, https://is.gd/cjIjvU, hidden folder %LOCALAPPDATA%\Microsoft\ lLctrJyDE, executable UserOOBEBrokervVW.exe.
• Mitigations: Block known malicious URLs, enforce least‑privilege execution, enable logging for Defender exclusion API calls.

*Source: SecurityAffairs – Image or Malware? Read until the end and answer in comments :)