Actively exploitedKnown ransomware use

CVE-2022-41352 Synacor Zimbra Collaboration Suite (ZCS) Arbitrary File Upload Vulnerability

Synacor Zimbra Collaboration Suite (ZCS) allows an attacker to upload arbitrary files using cpio package to gain incorrect access to any other user accounts.

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 20 Oct 2022.
CISA lists it as known to be used in ransomware campaigns.
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: Sandworm.
It has been in the catalogue for 1,478 days. Systems still unpatched now have almost certainly been scanned for it.

The Vulnerability

What It Is

An issue was discovered in Zimbra Collaboration (ZCS) 8.8.15 and 9.0. An attacker can upload arbitrary files through amavis via a cpio loophole (extraction to /opt/zimbra/jetty/webapps/zimbra/public) that can lead to incorrect access to any other user accounts. Zimbra recommends pax over cpio. Also, pax is in the prerequisites of Zimbra on Ubuntu; however, pax is no longer part of a default Red Hat installation after RHEL 6 (or CentOS 6). Once pax is installed, amavis automatically prefers it over cpio.

From Watch to Action

What To Do Now

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
Fix it
Apply updates per vendor instructions.
Vulnerability Management
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
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 Nov 2022 to remediate. A sensible benchmark for everyone else.

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

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All 19 exploited Synacor vulnerabilities

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CVE-2022-41352 Synacor Zimbra Collaboration Suite (ZCS) Arbitrary File Upload Vulnerability

Should You Worry?

What It Is

What To Do Now

Find it

Fix it

Hunt for compromise

Prove it is fixed

Vendor Advisories

The Compliance Clock

More Exploited Synacor Flaws

Not Sure If You Are Exposed?

Sources