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Zimbra Collaboration SuiteApplication · Synacor

CVE-2026-33368

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
Zimbra Collaboration Suite (ZCS) 10.0 and 10.1 contains a reflected cross-site scripting (XSS) vulnerability in the Classic Webmail REST interface (/h/rest). The application fails to properly sanitize user-supplied input, allowing an unauthenticated attacker to inject malicious JavaScript into a crafted URL. When a victim user accesses the link, the injected script executes in the context of the Zimbra webmail application, which could allow the attacker to perform actions on behalf of the victim.

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

Zimbra Collaboration Suite 10.0 and 10.1 contains a reflected cross-site scripting (XSS) vulnerability in the Classic Webmail REST endpoint (/h/rest). The application fails to properly sanitize user-supplied input in this endpoint, allowing an unauthenticated attacker to inject malicious JavaScript into a crafted URL that executes in the context of the victim's authenticated session.

MitigationApply vendor-supplied patch for CVE-2026-33368 to upgrade to a patched version of ZCS. Until patched, users should avoid clicking untrusted links and administrators may consider disabling or restricting the /h/rest endpoint.

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 ZCS version
    Run 'zmcontrol -v' or check /opt/zimbra/.git_description to determine the installed Zimbra Collaboration Suite version
    Affected if The installed version is 10.0.0 through 10.1.15 (any version >= 10.0.0 and < 10.1.16)
  2. Confirm Classic Webmail is enabled
    Check if the /h/rest endpoint is accessible by attempting to access https://<server>/h/rest or reviewing Zimbra proxy configuration files in /opt/zimbra/conf/nginx.conf
    Affected if The Classic Webmail interface and its /h/rest REST endpoint are enabled and reachable
  3. Verify webmail authentication configuration
    Review /opt/zimbra/conf/nginx.conf and /opt/zimbra/jetty/webapps/zimbra/public/h/rest.jsp (if exists) to confirm the endpoint handles user-supplied parameters without sanitization
    Affected if The /h/rest endpoint processes URL parameters without proper input validation

A user is affected if they are running ZCS version 10.0.0 through 10.1.15 with the Classic Webmail /h/rest endpoint enabled and accessible to users.

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

Apply vendor-supplied patch for CVE-2026-33368 to upgrade to a patched version of ZCS. Until patched, users should avoid clicking untrusted links and administrators may consider disabling or restricting the /h/rest endpoint.

Recommended fix Moderate confidence

Zimbra Collaboration Suite 10.1.16 or later

  1. 1. Back up your current Zimbra Collaboration Suite installation and database
  2. 2. Review Zimbra upgrade documentation for your current version
  3. 3. Download Zimbra Collaboration Suite version 10.1.16 or later from the official Zimbra repository
  4. 4. Execute the Zimbra upgrade installer on your server
  5. 5. Verify the upgrade completed successfully
  6. 6. Test the /h/rest endpoint to confirm the XSS vulnerability is remediated
  7. 7. Clear any browser caches and verify the webmail interface functions correctly
Caveat Review Zimbra 10.1.x release notes for any configuration or feature changes from your current 10.0.x version

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

Fix this in Zimbra Collaboration Suite Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA3.0 h
21.0 hours of engineering $3,680
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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-2026-33368 in production — separate from our analysis above.

No notes yet

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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