CVE-2026-73570: in the CISA KEV catalogue
Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability. CISA added CVE-2026-73570 to the Known Exploited Vulnerabilities catalogue on 2026-08-21 with a default due date of 2026-08-24. Known ransomware campaign use: Unknown. Forensic triage flag: Yes.
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. (CISA description)
- Vendor / product
- Synacor Zimbra Collaboration Suite (ZCS)
- CWE
- CWE-78
- CISA required action
- 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.
- EPSS
- 72%, percentile 99 (scored 2026-11-04)
EPSS puts about 72 in 100 odds (72%) on exploitation activity being observed in the next 30 days. Its score is higher than or equal to that of 99% of scored CVEs. This is a model estimate about exploitation anywhere, not about your environment.
Vendor and reference links (from CISA)
- https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories
- https://blog.zimbra.com/2026/07/patch-release-update-zimbra-10-1-20/
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- 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
Your own deadline under CISA BOD 26-04 depends on exposure, automatability and technical impact: work it out with the BOD 26-04 calculator.
Frequently asked questions
Is CVE-2026-73570 in the CISA KEV catalogue?
Yes. CISA added CVE-2026-73570 (Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability) to the Known Exploited Vulnerabilities catalogue on 2026-08-21. CISA's default due date for it is 2026-08-24.
Is CVE-2026-73570 used in ransomware attacks?
CISA marks known ransomware campaign use as Unknown for CVE-2026-73570. That means CISA lacks confirmation, not that ransomware groups do not use it.
What should I do about CVE-2026-73570?
CISA's required action: 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.
Sources
- CISA, Known Exploited Vulnerabilities Catalog (accessed 2026-11-03)
- FIRST, Exploit Prediction Scoring System (EPSS) (EPSS by FIRST; scores generated by Empirical Security)
- NVD record for CVE-2026-73570