+44 1865 950 828 Secure Your Business
Actively exploited

CVE-2019-9670 Synacor Zimbra Collaboration Suite (ZCS) Improper Restriction of XML External Entity Reference

Synacor Zimbra Collaboration Suite (ZCS) contains an improper restriction of XML external entity (XXE) vulnerability in the mailboxd 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 10 Jan 2022.
  • Rated Critical severity (CVSS 9.8, scored by CISA).
  • This product type is often exposed to the internet, which is where attackers scan for it first.
  • Named in Cybergen threat actor reporting: APT29.
  • It has been in the catalogue for 1,761 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

mailboxd component in Synacor Zimbra Collaboration Suite 8.7.x before 8.7.11p10 has an XML External Entity injection (XXE) vulnerability, as demonstrated by Autodiscover/Autodiscover.xml.

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 updates per vendor instructions.

    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 critical, 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 10 Jul 2022 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

Get alerts for SynacorWe email you when a new Synacor vulnerability is confirmed as exploited. Add more vendors on Threat Watch.

By signing up you agree to receive Threat Watch alerts. Unsubscribe at any time. See our Privacy Policy.

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-2019-9670 and every other exploited flaw on the list.

Check My Exposure
Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2019-9670
  3. CVE record: CVE-2019-9670
  4. FIRST EPSS
  5. wiki.zimbra.com/wiki/Zimbra_Security_Advisories
  6. bugzilla.zimbra.com/show_bug.cgi?id=109129
  7. rapid7.com/db/modules/exploit/linux/http/zimbra_xxe_rce
  8. packetstormsecurity.com/files/152487/Zimbra-Collaboration-Autodiscover-Servlet-XXE-ProxyServlet-SSRF
  9. exploit-db.com/exploits/46693/
  10. isc.sans.edu/forums/diary/CVE20199670+Zimbra+Collaboration+Suite+XXE+vulnerability/27570/