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Known exploited vulnerability · CISA KEV

CVE-2026-73570: Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability

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.

CVE-2026-73570

Exploited in the wild. Fix this first.

CISA added it to the Known Exploited Vulnerabilities catalog on 2026-08-21: attackers are using it right now.

CISA KEV
Listed
Added 2026-08-21 · federal fix-by 2026-08-24
EPSS (30 days)
72%
Higher than 99.4% of CVEs · 2026-11-01
CVSS
No score

What CISA says

Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability

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.

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How to check if you are exposed to CVE-2026-73570

  1. Find every Synacor Zimbra Collaboration Suite (ZCS) system you or your clients run, including ones exposed to the internet. Those come first: CISA only lists flaws attackers are already using.
  2. Compare each version with the fixed versions in the vendor advisory below. Where no fix exists yet, apply the vendor’s mitigation or take the system off the internet.
  3. Run a credentialed vulnerability scan to catch the systems you missed, then check that the next scan no longer reports CVE-2026-73570.

US federal agencies had to fix this by 2026-08-24. Everyone else should treat that deadline as a guide: if it has passed, this is overdue.

Timeline

  1. · Added to CISA's Known Exploited Vulnerabilities catalog
  2. · Fix-by date for US federal agencies, passed 69 days ago

Vendor advisories and fixes

Weakness type

More exploited Synacor vulnerabilities

CISA lists 19 exploited Synacor vulnerabilities. The closest matches:

Keep going

Sources: CISA Known Exploited Vulnerabilities catalog (version 2026.10.30); EPSS data from FIRST.org; CVSS and descriptions from the NIST National Vulnerability Database. Checked 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.

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