Zimbra Collaboration Suite Classic Web Client Stored Cross-Site Scripting via Crafted Calendar COUNTER Message From Address (CVE-2026-93647) | HOL Guard CVE

Critical · CVSS 9.3CVE-2026-93647

Zimbra Collaboration Suite Classic Web Client Stored Cross-Site Scripting via Crafted Calendar COUNTER Message From Address

Answer in brief

CVE-2026-93647 records a Critical severity (CVSS 9.3) vulnerability in Zimbra Collaboration Suite Classic Web Client Stored Cross-Site Scripting via Crafted Calendar COUNTER Message From Address. The current sources do not mark it as known exploited. The current feed maps Zimbra/Zimbra Collaboration Suite (ZCS) (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 25, 2026Updated Sep 25, 2026Source checked Sep 25, 2026First seen by HOL Sep 25, 2026Material review Sep 25, 2026

Upstream Advisory

Key facts

Risk: Critical · CVSS 9.3
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 9.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Zimbra/Zimbra Collaboration Suite (ZCS) (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Zimbra/Zimbra Collaboration Suite (ZCS)generic	>=0 <10.1.21	10.1.21

Recommended response

Check inventory. Check lockfiles and deployed manifests for Zimbra/Zimbra Collaboration Suite (ZCS).
Review the reported fix. Update Zimbra/Zimbra Collaboration Suite (ZCS) to 10.1.21 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 25, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 25, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 25, 2026

Sources and claim methodology

Source referencewiki.zimbra.com

Upstream source description

An unauthenticated calendar sender can place active markup in a COUNTER message's RFC From address. Selecting the message in Zimbra Classic triggers stored XSS, allowing the attacker to access mailbox data and act as the victim.

Quoted source text, attributed separately from HOL analysis.