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Zimbra Collaboration SuiteApplication · Synacor

CVE-2026-33370

MEDIUM · 6.1 CVSS v3.1 Published 2026-03-20
Fix available
A fix is available. Upgrade to 10.1.16 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
An issue was discovered in Zimbra Collaboration (ZCS) 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Zimbra Briefcase feature due to insufficient sanitization of specific uploaded file types. When a user opens a publicly shared Briefcase file containing malicious scripts, the embedded JavaScript executes in the context of the user's session. This allows an attacker to run arbitrary scripts, potentially leading to data exfiltration or other unauthorized actions on behalf of the victim user.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A stored XSS vulnerability exists in Zimbra Collaboration (ZCS) versions 10.0 and 10.1 within the Briefcase feature. Attackers can upload files containing malicious JavaScript that aren't properly sanitized. When victims access publicly shared Briefcase files, the embedded script executes in their session context, enabling data exfiltration and unauthorized actions.

MitigationUpgrade to a patched version of ZCS that addresses this vulnerability, and implement proper sanitization/validation of file content in the Briefcase feature before serving uploaded files to users.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Zimbra Collaboration SuiteApplication
Affected:>= 10.0.0, < 10.1.16

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed ZCS version
    Run 'zmcontrol -v' or check '/opt/zimbra/.install_history' to get the exact Zimbra Collaboration Suite version number
    Affected if The installed version is 10.0.0 or any 10.0.x through 10.1.x version below 10.1.16
  2. Verify Briefcase module is enabled
    Check if the Briefcase feature is active by logging into the ZCS admin console or running 'zmprov gs $(hostname) zimbraFeatureBriefcaseEnabled'
    Affected if Briefcase is enabled (returns TRUE) - the vulnerability only applies when Briefcase is available
  3. Confirm public sharing configuration
    Review the Briefcase sharing settings via admin console or check 'zmprov gacf | grep -i briefcase' to see if public links or external sharing is permitted
    Affected if Public/external sharing is enabled for Briefcase files - the XSS triggers when victims access publicly shared files
  4. Inspect recent Briefcase uploads
    Review uploaded files in /opt/zimbra/data/amavisd/virusmails or the Briefcase storage directory under /opt/zimbra/store/0/*/briefcase for unexpected file types or content
    Affected if Files with embedded scripts (HTML, SVG, or renamed executables with malicious content) are present in Briefcase
  5. Check server logs for XSS indicators
    Search mail.log, nginx.access.log, or Zimbra logs for patterns like '<script', 'javascript:', or 'onerror=' in Briefcase-related requests
    Affected if Logs show suspicious URL patterns or attempted XSS payloads in Briefcase access logs

You are affected if running any ZCS version from 10.0.0 to below 10.1.16 AND the Briefcase feature is enabled with public sharing configured.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 10.1.16 or later
Fixed in 10.1.16
Interim mitigation

Upgrade to a patched version of ZCS that addresses this vulnerability, and implement proper sanitization/validation of file content in the Briefcase feature before serving uploaded files to users.

Recommended fix High confidence

10.1.16 or later

  1. Review Zimbra upgrade documentation for version 10.1.x
  2. Plan and schedule a maintenance window for the upgrade
  3. Perform a complete backup of the Zimbra Collaboration Suite including database, mail store, and configuration
  4. Test the upgrade in a staging environment before applying to production
  5. Upgrade Zimbra Collaboration Suite from current version (10.0.0 - 10.1.15) to version 10.1.16 or later
  6. Verify the Briefcase feature functions correctly after the upgrade
  7. Confirm the vulnerability is remediated by testing that uploaded files are properly sanitized
Caveat Standard Zimbra upgrade migration procedures apply; test thoroughly in staging before production deployment

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Zimbra Collaboration Suite Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing6.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,980
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-33370 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data