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Actively exploited

CVE-2019-9621 Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery (SSRF) Vulnerability

Synacor Zimbra Collaboration Suite (ZCS) contains a server-side request forgery (SSRF) vulnerability via the ProxyServlet component.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 7 Jul 2025.
  • Rated High severity (CVSS 7.5, scored by CISA).
  • This product type is often exposed to the internet, which is where attackers scan for it first.
  • It has been in the catalogue for 487 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

Zimbra Collaboration Suite before 8.6 patch 13, 8.7.x before 8.7.11 patch 10, and 8.8.x before 8.8.10 patch 7 or 8.8.x before 8.8.11 patch 3 allows SSRF via the ProxyServlet component.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Synacor Zimbra Collaboration Suite (ZCS). Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated high, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 28 Jul 2025 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited Synacor Flaws

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CVE-2026-73570Zimbra Collaboration Suite (ZCS) OS Command Injection VulnerabilityAdded 21 Aug 2026CVE-2025-48700Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting VulnerabilityAdded 20 Apr 2026CVE-2025-66376Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting VulnerabilityAdded 18 Mar 2026CVE-2020-7796Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery VulnerabilityAdded 17 Feb 2026CVE-2025-68645Synacor Zimbra Collaboration Suite (ZCS) PHP Remote File Inclusion VulnerabilityAdded 22 Jan 2026CVE-2025-27915Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting VulnerabilityAdded 7 Oct 2025

All 19 exploited Synacor vulnerabilities

Not Sure If You Are Exposed?

Our attack surface and vulnerability teams can check your internet-facing estate for CVE-2019-9621 and every other exploited flaw on the list.

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2019-9621
  3. CVE record: CVE-2019-9621
  4. FIRST EPSS
  5. wiki.zimbra.com/wiki/Zimbra_Security_Advisories
  6. wiki.zimbra.com/wiki/Security_Center
  7. bugzilla.zimbra.com/show_bug.cgi?id=109127
  8. rapid7.com/db/modules/exploit/linux/http/zimbra_xxe_rce
  9. packetstormsecurity.com/files/152487/Zimbra-Collaboration-Autodiscover-Servlet-XXE-ProxyServlet-SSRF
  10. exploit-db.com/exploits/46693/
  11. blog.zimbra.com/2019/03/9826/
  12. blog.tint0.com/2019/03/a-saga-of-code-executions-on-zimbra.html