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Exploited vulnerability · CISA KEV

Is CVE-2024-27443 exploited? Yes: in CISA KEV since 19 May 2025

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

Yes. CVE-2024-27443, Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 19 May 2025, 280 days after it was published. It affects Synacor Zimbra Collaboration Suite (ZCS). If you run it, CISA's required action is: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

exploitedYesCISA KEV · 19 May 2025
ransomwareNot knownno confirmed use
EPSStop 5%very likely to be exploited
severity6.1CVSS 3.1 · medium
US federal due9 Jun 2025BOD 22-01 deadline

What it is

Zimbra Collaboration contains a cross-site scripting (XSS) vulnerability in the CalendarInvite feature of the Zimbra webmail classic user interface. An attacker can exploit this vulnerability via an email message containing a crafted calendar header, leading to the execution of arbitrary JavaScript code.

VendorSynacor (19 exploited CVEs in KEV)
ProductZimbra Collaboration Suite (ZCS)
VulnerabilitySynacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
WeaknessCWE-79
Published12 Aug 2024
Added to KEV19 May 2025
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 per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
  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 12 Aug 2024.
  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-2024-27443 being exploited?

Yes. CISA added CVE-2024-27443 to the Known Exploited Vulnerabilities catalog on 19 May 2025, which means there is reliable evidence of exploitation in the wild.

Is CVE-2024-27443 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-2024-27443?

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. 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 May 2025 · Synacor scorecard · act-now radar.

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