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Exploited vulnerability · CISA KEV

Is CVE-2026-73570 exploited? Yes: in CISA KEV since 21 Aug 2026

Gociux · Synacor Zimbra Collaboration Suite (ZCS) · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2026-73570, Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 21 Aug 2026, 8 days after it was published. It affects Synacor Zimbra Collaboration Suite (ZCS). If you run it, CISA's required action is: 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.

exploitedYesCISA KEV · 21 Aug 2026
ransomwareNot knownno confirmed use
EPSStop 1%among the most likely CVEs to be exploited
severity8.9CVSS 3.1 · high
US federal due24 Aug 2026BOD 22-01 deadline

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.

VendorSynacor (19 exploited CVEs in KEV)
ProductZimbra Collaboration Suite (ZCS)
VulnerabilityZimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability
WeaknessCWE-78
Published13 Aug 2026
Added to KEV21 Aug 2026
Reported by (CNA)mitre

What to do

  1. Check whether you run it. Look for Zimbra Collaboration Suite (ZCS) in your asset inventory, including appliances and cloud images. Stack check lists every exploited Synacor CVE at once.
  2. Apply the fix. 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.
  3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 13 Aug 2026.
  4. Get told next time. Email alerts when CISA adds a CVE for Synacor.

Other exploited CVEs in Zimbra Collaboration Suite (ZCS)

References

Questions

Is CVE-2026-73570 being exploited?

Yes. CISA added CVE-2026-73570 to the Known Exploited Vulnerabilities catalog on 21 Aug 2026, which means there is reliable evidence of exploitation in the wild.

Is CVE-2026-73570 used in ransomware attacks?

CISA does not list known ransomware use for it. That can change, and exploitation alone is reason to fix it first.

How do I fix CVE-2026-73570?

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. Check Synacor's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected Zimbra Collaboration Suite (ZCS) and watch it for signs of compromise.

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in August 2026 · Synacor scorecard · act-now radar.

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