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TI-2026-79908 Aliases CVE-2026-93627GHSA-77gq-8m6p-2c3g

Authentication bypass in Zimbra calendar processing

Priority LOW 30CWE-290Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Security bypass
Confidentiality · integrity · availability
None · Low · None
Fix status
No fix listed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-290.

Summary

Zimbra Collaboration Suite through 10.1.21 is affected. Email calendar processing does not verify that the sender is authorized to act as the iCalendar organizer, a spoofing flaw classified as CWE-290. An unauthenticated remote attacker who knows a meeting's UID and organizer address can move or replace that meeting in a recipient's calendar by sending a crafted email. Processing happens automatically during delivery, without recipient interaction.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

Description from the CNA

An organizer authentication vulnerability in the email calendar processing of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to cancel or modify an existing meeting in a recipient's calendar. Zimbra accepts iCalendar CANCEL and REQUEST components without verifying that the email sender is authorized to act as the supplied organizer. An attacker who knows the meeting UID and organizer address can supply a non-outdated sequence number to move the recipient's meeting to Trash or replace its details. Processing occurs automatically during email delivery without recipient interaction. ZCS 10.1.16 and 10.1.21 are affected.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00268 19th percentileScored 2026-11-07
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
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
ZimbraZimbra Collaboration Suiteup to 10.1.21—No fix listedCNA
  • Zimbra Collaboration Suite VendorZimbra Affected up to 10.1.21 Fixed in — No fix listed CNA

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:*——Synacor
  • cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:* Versions — — ·Synacor

Remediation

The sources list no fixed version for Zimbra Collaboration Suite.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

Timeline

  1. 2026-10-23 Threatist record created from CVE-2026-93627
  2. 2026-10-23 Alias added: GHSA-77gq-8m6p-2c3g
  3. 2026-10-28 CISA SSVC decision points changed

References

Advisory 1

Other 1

  • TI-2026-51660 OS command injection in Zimbra Collaboration KEVCVSS 3.1HIGH 8.9
  • TI-2025-40820 Cross-site scripting in Zimbra Collaboration KEVCVSS 3.1HIGH 7.2
  • TI-2024-18266 An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0. KEVCVSS 3.1MEDIUM 6.1
  • TI-2024-30553 An issue was discovered in Zimbra Collaboration (ZCS) 10.1.x before 10.1.1, 10.0.x before… CVSS 3.1HIGH 8.8
  • TI-2022-13998 Zimbra Collaboration Open Source 8.8.15 does not encrypt the initial-login randomly… CVSS 3.1CRITICAL 9.8
  • TI-2026-63080 Path traversal in Zimbra Collaboration Suite CVSS 3.1CRITICAL 9.8
See all 94 →

Sources

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