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VulnerabilityPublished Updated

CVE-2026-93647: Zimbra Collaboration Suite (ZCS) · Cross-site Scripting

Affects Zimbra Collaboration Suite (ZCS)Source CVE Database V5

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Not known to be exploited · CVSS 9.3 Critical : upgrade to 10.1.21 as a priority.

Data as of 8 Nov 2026, 23:24 UTC

CVSS 3.1 base score
9.3Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 13% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 10.1.21
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 25 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 8 Nov 2026.

What to do

Upgrade Zimbra Collaboration Suite (ZCS) to 10.1.21.

Affected software

ProductAffectedFixed in
ZimbraZimbra Collaboration Suite (ZCS)Affected
  • <10.1.21
Fixed in
  • 10.1.21

AI-suggested

If you cannot patch yet, users should exercise caution when interacting with calendar messages from untrusted sources. Consider disabling or restricting calendar message rendering in Zimbra Classic if possible.

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.

References

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