Synacor Zimbra Collaboration Suite (ZCS)

What it is

Zimbra Collaboration Suite (ZCS) contains an OS command injection vulnerability which could allow an unauthenticated attacker to send specially crafted SMTP requests that may result in execution of arbitrary operating system commands as the Zimbra user.

What to do

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.

Vendor notices and references

• wiki.zimbra.com/wiki/Zimbra_Security_Advisories
• blog.zimbra.com/2026/07/patch-release-update-zimbra-10-1-20/
• nvd.nist.gov/vuln/detail/CVE-2026-73570

Description and required action as published by CISA. Full record at NVD.