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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 9 Jun 2025.
CollaborationApplication · Zimbra

CVE-2024-27443

MEDIUM · 6.1 CVSS v3.1 Published 2024-08-12
Fix available
A fix is available. Upgrade to 10.0.7 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild 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) 9.0 and 10.0. A Cross-Site Scripting (XSS) vulnerability exists in the CalendarInvite feature of the Zimbra webmail classic user interface, because of improper input validation in the handling of the calendar header. An attacker can exploit this via an email message containing a crafted calendar header with an embedded XSS payload. When a victim views this message in the Zimbra webmail classic interface, the payload is executed in the context of the victim's session, potentially leading to execution of arbitrary JavaScript code.

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 Cross-Site Scripting (XSS) vulnerability exists in Zimbra Collaboration 9.0 and 10.0's CalendarInvite feature within the classic webmail UI. Attackers embed malicious JavaScript in calendar header fields via specially crafted email messages. When recipients view these messages, the payload executes in their browser session context due to improper input validation.

MitigationImplement strict input validation and output encoding for calendar header fields to prevent script execution. Apply context-specific sanitization before rendering calendar invite data in the webmail interface.

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
CollaborationApplication
Affected:>= 10.0.0, < 10.0.7= 9.0.0

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. Check Zimbra Collaboration version
    Use the Zimbra administration console or run 'zmcontrol -v' or 'zmmsgq -v' from the Zimbra server command line to identify the installed version.
    Affected if The installed version is 9.0.0 or falls in the range 10.0.0 through 10.0.6 (anything less than 10.0.7).
  2. Verify classic webmail interface is enabled
    Access the Zimbra administration console, navigate to the Zimbra Web Client settings, or check the server configuration for the 'classic' web client mode being active. Alternatively, check if users can access the classic webmail URL pattern (typically /zimbra/mail).
    Affected if The classic webmail interface is enabled and accessible to end users.
  3. Confirm mail processing includes calendar invites
    Verify that the Zimbra server processes inbound email with calendar invitations (iCalendar content). This is default behavior in standard Zimbra configurations.
    Affected if Calendar processing is enabled, which is the default configuration.

A user is affected if they run Zimbra version 9.0.0 or 10.0.0-10.0.6 with the classic webmail interface enabled and calendar invite processing active.

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 10.0.7 or later
Fixed in 10.0.7
Interim mitigation

Implement strict input validation and output encoding for calendar header fields to prevent script execution. Apply context-specific sanitization before rendering calendar invite data in the webmail interface.

Recommended fix Moderate confidence

ZCS 10.0.7 or later (for 10.0.x line); ZCS 9.0 series patched release or migrate to 10.0.7+ (for 9.0.0)

  1. 1. Identify the current Zimbra Collaboration version by running: zmcontrol -v or checking the admin console
  2. 2. For ZCS 10.0.x: Plan an upgrade to version 10.0.7 or later as the patched release
  3. 3. Review Zimbra upgrade documentation for your current version at wiki.zimbra.com
  4. 4. Schedule a maintenance window and backup the current ZCS installation including the LDAP directory and mail stores
  5. 5. Perform a test upgrade in a non-production environment first
  6. 6. Execute the upgrade following Zimbra's standard upgrade procedure for your operating system
  7. 7. After upgrade, verify the CalendarInvite feature functions correctly and the XSS vulnerability is resolved by testing with a calendar header containing HTML/script content
Caveat Review Zimbra 10.0.7 release notes for any configuration or feature changes; ensure custom Zimlets are compatible with the target version

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

Fix this in Collaboration Exploited in the wild — priority engagement
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
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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-2024-27443 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