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Actively exploitedKnown ransomware use

CVE-2022-24682 Synacor Zimbra Collaborate Suite (ZCS) Cross-Site Scripting Vulnerability

Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting (XSS) vulnerability in the Calendar feature that allows an attacker to execute arbitrary code.

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 25 Feb 2022.
  • CISA lists it as known to be used in ransomware campaigns.
  • Rated Medium severity (CVSS 6.1, 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 1,715 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

An issue was discovered in the Calendar feature in Zimbra Collaboration Suite 8.8.x before 8.8.15 patch 30 (update 1), as exploited in the wild starting in December 2021. An attacker could place HTML containing executable JavaScript inside element attributes. This markup becomes unescaped, causing arbitrary markup to be injected into the document.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Synacor Zimbra Collaborate 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 EssentialsCyber Essentials requires high and critical updates (CVSS 7.0 or above) within 14 days of release. Treat any exploited flaw the same way.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 11 Mar 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

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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?

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2022-24682
  3. CVE record: CVE-2022-24682
  4. FIRST EPSS
  5. wiki.zimbra.com/wiki/Zimbra_Security_Advisories
  6. wiki.zimbra.com/wiki/Security_Center
  7. volexity.com/blog/2022/02/03/operation-emailthief-active-exploitation-of-zero-day-xss-vulnerability-
  8. blog.zimbra.com/2022/02/hotfix-available-5-feb-for-zero-day-exploit-vulnerability-in-zimbra-8-8-15/
  9. wiki.zimbra.com/wiki/Zimbra_Releases/8.8.15/P30