CVE-2026-73570: Zimbra Log File Abuse Enables Remote Code Execution

Summary

CVE-2026-73570 is an unauthenticated command injection vulnerability affecting Zimbra email collaboration software. An attacker can trigger the flaw by sending a crafted SMTP RCPT TO request that generates a specific entry in /var/log/zimbra.log. The Swatchdog daemon later parses this entry through a vulnerable Perl script, allowing arbitrary remote code execution with the privileges of the zimbra user.

Investigation

Researchers reproduced the complete exploit chain by sending malformed SMTP messages and analyzing the resulting log entries. They found that many public PoCs fail because they do not generate the exact Service status change pattern required by the Swatchdog daemon. The investigation confirmed that command injection is possible through backticks processed by the Perl script responsible for SNMP notifications.

Mitigation

The primary mitigation is upgrading Zimbra to version 10.1.20 or later. Organizations should also deploy monitoring through security tools such as Elastic Defend to identify anomalous shell execution originating from the Swatchdog Perl process.

Response

When exploitation is suspected, investigators should hunt for common RCE indicators, including suspicious shell or bash child processes spawned by Perl. Defenders should also monitor for unauthorized access to local databases, signing keys, LDAP exports, and unusual phishing activity originating from the compromised Zimbra mail server.

Simulation Execution

• Attack Narrative & Commands: An attacker has successfully identified a command injection vulnerability in a Perl-based monitoring utility. To establish a footprint and begin reconnaissance, the attacker injects a payload that forces the Perl interpreter to spawn a bash shell. This allows the attacker to execute complex commands through the service’s context. The goal is to produce a process tree where bash is a direct child of a perl process, thereby triggering the detection rule.

• Regression Test Script:

  #!/bin/bash
  # Simulation script to trigger Zimbra Swatchdog Shell Process Detection
  # This mimics a command injection spawning a shell from Perl.
  
  echo "[*] Starting Simulation: Spawning bash from perl..."
  
  # Use perl to execute a shell command. 
  # This creates the process hierarchy: perl -> bash
  perl -e 'system("/bin/bash -c "echo SIMULATION_SUCCESSFUL"")'
  
  echo "[*] Simulation complete. Check your SIEM for alerts."

• Cleanup Commands:

  # No persistent artifacts are created by this simulation.
  # No cleanup required.