~/exploited / cve-2026-73570

CVE-2026-73570: Synacor Zimbra Collaboration Suite (ZCS)

According to CISA this vulnerability is already used in attacks (added on 21 August 2026).

Key facts

Description (CISA)

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.

Required action (CISA)

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.

What admins should do now

1. Affected? Check whether Synacor Zimbra Collaboration Suite (ZCS) is in use and which version runs (package manager, admin UI, --version).
2. Apply the vendor patch or workaround as soon as it exists. If that is not possible right away: restrict outside access (firewall, VPN, reverse proxy).
3. Review logs back to 21 August 2026: unusual logins, new files, unexpected processes, outbound connections.
4. If you suspect a compromise: isolate the system, rotate credentials, check the last backup from before the incident.

The deadline applies to US federal agencies. It is still a useful yardstick for everyone: when a flaw is attacked in the wild, waiting is not an option.

Sources

• CISA KEV Catalog
• NVD CVE-2026-73570
• wiki.zimbra.com/wiki/Zimbra_Security_Advisories
• blog.zimbra.com/2026/07/patch-release-update-zimbra-10-1-20/
• www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-base
• www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizi
• nvd.nist.gov/vuln/detail/CVE-2026-73570

Data: CISA Known Exploited Vulnerabilities Catalog, as of 30 October 2026. No guarantee — always check the vendor's advisory.

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