CVE-2026-73570 — Synacor Zimbra Collaboration Suite (ZCS): OS Command Injection | CVSS 8.9 HIGH

HIGH

CVSS 8.9 HIGH  ·  EPSS 1%  ·  Synacor Zimbra Collaboration Suite (ZCS)

Severity Overview

Summary

A remote code execution vulnerability exists in Zimbra Collaboration (ZCS) before 10.1.20 when the optional zimbra-snmp package is installed and SNMP notifications are enabled. Due to improper sanitization of untrusted input during SNMP notification processing, an unauthenticated attacker can send specially crafted SMTP requests that may result in execution of arbitrary operating system commands as the Zimbra user.

What the Attack Looks Like

How it works: Attacker-controlled input is passed directly to a system command without sanitization. The OS executes the injected commands with the privileges of the application process.

If successfully exploited: Because this vulnerability has a scope change, the impact extends beyond the vulnerable component — adjacent services or system resources may be compromised as well. Full confidentiality and integrity impact means an attacker can both read and modify sensitive data — useful for credential harvesting, data theft, or manipulating application state.

Analyst Takeaway

The attack is launched over the network (remotely exploitable without physical access) and no authentication is required. Exploitation requires specific conditions to be met (high attack complexity), which may reduce reliability in opportunistic campaigns. A successful exploit can break out of the vulnerable component and affect other system resources (scope change), potentially enabling broader compromise. This vulnerability is already in CISA KEV, which means exploitation has been confirmed in the wild — treat this as active risk, not theoretical exposure. The CVSS score is high enough to justify expedited remediation, especially for exposed systems or assets that handle sensitive data. In parallel with patching, defenders should review external exposure, hunt for signs of exploitation, and validate whether compensating controls are in place for vulnerable assets.

MITRE ATT&CK Mapping

• T1195.002 – Compromise Software Supply Chain
  Rationale: The vulnerability context suggests compromise of software or its delivery/update path.

Detection Guidance

• CWE-78 — OS Command Injection
  • Application and WAF logs: Search for shell metacharacters in request parameters: semicolons, pipes (|), ampersands (&), backticks, $(, %0a (URL-encoded newline), and their double-encoded variants.
  • Process telemetry: Hunt for shell interpreters (bash, sh, zsh, cmd.exe, PowerShell) spawned as direct children of the application or web server process. This parent-child chain is rarely legitimate and warrants immediate investigation.
  • Executed command patterns: After initial injection, attackers commonly run: id, whoami, uname -a (reconnaissance), followed by curl or wget to retrieve secondary payloads. Search process command-line telemetry for these sequences.
  • Sysmon / auditd: On Windows, Sysmon Event 1 with a web server parent spawning cmd.exe or PowerShell is high-fidelity. On Linux, auditd execve syscall records from the application user are key.
• T1195.002 — Software Supply Chain Compromise
  • Validate integrity of software updates, packages, and repositories associated with the affected product against known-good vendor hashes.
  • Review CI/CD pipeline activity, build logs, and package download history for anomalies around the vulnerability disclosure window.
  • Confirm software was sourced from official vendor channels and that update infrastructure communications match expected vendor endpoints.

Hunting Considerations

These are proactive hunts mapped to the ATT&CK techniques identified for this CVE. Run them now — do not wait for an alert to fire.

• T1195.002 — Software Supply Chain Compromise
  • Binary integrity: Compare hashes of recently updated software packages and executables against known-good values from the vendor’s official release. Unexpected hash changes in software update paths are the primary supply chain indicator.
  • Build system activity: Review CI/CD pipeline logs for unexpected jobs, unauthorized commits, changes to build scripts, or outbound network connections from build servers to external IPs not in your allowlist.
  • Update server communications: Flag connections to update endpoints that do not resolve to known vendor infrastructure. Supply chain attacks commonly involve redirecting update traffic to attacker-controlled servers.
  • Prioritize recently updated systems: Identify all hosts running the affected product version and focus investigation on those that applied updates during the window of potential compromise — an update received during an active supply chain attack is the highest-risk scenario.

Recommended Actions

Immediate (0–24 Hours)

• Inventory: Identify all systems running Synacor Zimbra Collaboration Suite (ZCS). Include production, staging, dev, and cloud environments — untracked instances are the most likely to remain unpatched.
• Validate internet-facing exposure: Determine which of the affected systems are reachable from the public internet. Prioritize these for immediate remediation or compensating controls.
• Verify software integrity: Before applying updates, confirm that software packages and update mechanisms have not been tampered with. Compare hashes against vendor-published values.

Remediation

• Apply the vendor patch: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
• CISA directive deadline: 2026-08-24 — this is the mandatory deadline for US federal civilian agencies under BOD 22-01. All organizations should treat this date as a strong target regardless of federal mandate.
• Verify remediation: After patching, confirm the correct version is installed on all affected hosts. Run a vulnerability scan or use your asset management tooling to verify — do not rely solely on change tickets.

Detection Coverage

• Verify ATT&CK coverage: Confirm your SIEM and EDR have detection logic in place for T1195.002. Review the Detection Guidance and Hunting Considerations sections of this alert for the specific log sources and behavioral patterns to monitor.
• Unauthenticated exploitation monitoring: Because this vulnerability requires no authentication, internet-facing scanning and exploitation attempts may begin within hours of public disclosure. Ensure alerting is in place before the end of the day.
• Threat intelligence feeds: Monitor your TI feeds and vendor advisory channels for published indicators of compromise (IOCs), proof-of-concept exploit releases, or active campaign reporting associated with this CVE — these should trigger an immediate hunt even if no internal alerts have fired.

Detection Playbooks

Vulnerability Details

Additional Notes

https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories ; https://blog.zimbra.com/2026/07/patch-release-update-zimbra-10-1-20/ ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2026-73570