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TI-2026-82517 Aliases CVE-2026-66912GHSA-rprc-q5mj-4mcw

Stored cross-site scripting in Zimbra Collaboration via From header

Priority LOW 24CWE-79Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Passive
Attack complexity
Low
Attack requirements
None
Impact type
Cross-site scripting
Confidentiality · integrity · availability
None · None · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-79.

Summary

Zimbra Collaboration before 10.1.21 is vulnerable to stored cross-site scripting through the From email header during HTML reply composition in Classic UI. Insufficient sanitization of the From header value lets a remote attacker send a crafted email that carries a JavaScript payload (CWE-79). When the victim opens the message in Classic UI and clicks Reply while composing in HTML mode with reply headers disabled, the script runs in the victim's browser and can steal session information or act on the victim's behalf. The attack requires user interaction, and no privileges are required.

Written with Claude Haiku 5.5 from the sources below · 2026-11-05

Description from the CNA

Zimbra is vulnerable to Stored Cross-Site Scripting (XSS) via the From email header during HTML reply composition in Classic UI. Due to insufficient sanitization of the From header value, a remote attacker can send a crafted email containing a malicious From header with an embedded JavaScript payload. When the victim opens the message in Classic UI and clicks Reply while composing in HTML mode with reply headers disabled, the unsanitized From header content is rendered as HTML and the JavaScript payload executes in the victim's browser, potentially allowing the attacker to steal session information or perform actions on behalf of the victim. This issue was fixed in version 10.1.21

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00467 40th percentileScored 2026-11-07
Fix Fixed Zimbra Collaboration (Synacor): 10.1.21

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
SynacorZimbra Collaborationbefore 10.1.2110.1.21Patch availableCNA
  • Zimbra Collaboration VendorSynacor Affected before 10.1.21 Fixed in 10.1.21 Patch available CNA

Remediation

Upgrade Zimbra Collaboration to version 10.1.21.

Written with Claude Haiku 5.5 from the sources below · 2026-11-05

  • Fix · CNA Zimbra Collaboration (Synacor) Fixed in 10.1.21

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    Synacor Zimbra Collaboration 10.1.21

    2 records Highest priority Priority LOW 2 LOW

    Other records, highest priority first

    • TI-2026-82516 Stored cross-site scripting in Zimbra via email attachmentsPriority LOW 25
    Show all 2 records →

Timeline

  1. 2026-10-29 Threatist record created from CVE-2026-66912
  2. 2026-10-29 Alias added: GHSA-rprc-q5mj-4mcw
  3. 2026-11-05 CISA SSVC decision points changed

References

Advisory 1

Other 1

  • TI-2024-30554 The postjournal service in Zimbra Collaboration (ZCS) before 8.8.15 Patch 46, 9 before… KEVCVSS 3.1CRITICAL 10.0
  • TI-2022-19841 An issue was discovered in Zimbra Collaboration (ZCS) 8.8.15 and 9.0. KEVCVSS 3.1CRITICAL 9.8
  • TI-2022-17239 Zimbra Collaboration Suite (ZCS) 8.8.15 and 9.0 has mboximport functionality that… KEVCVSS 3.1CRITICAL 9.8
  • TI-2022-10792 Zimbra Collaboration (aka ZCS) 8.8.15 and 9.0 allows an unauthenticated attacker to… KEVCVSS 3.1CRITICAL 9.8
  • TI-2020-06312 Zimbra Collaboration Suite (ZCS) before 8.8.15 Patch 7 allows SSRF when WebEx zimlet is… KEVCVSS 3.1CRITICAL 9.8
  • TI-2019-07076 mailboxd component in Synacor Zimbra Collaboration Suite 8.7.x before 8.7.11p10 has an… KEVCVSS 3.1CRITICAL 9.8
See all 105 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences