CVE-2026-93628: CWE-290 Authentication bypass by spoofing in Zimbra Zimbra Collaboration Suite
Description
CVE-2026-93628 is an authentication bypass vulnerability in Zimbra Collaboration Suite's email calendar processing. It allows an unauthenticated attacker to spoof an attendee's response to a meeting by exploiting how Zimbra processes iCalendar REPLY components with a null sender identity. This causes the attendee authorization check to be skipped, enabling unauthorized changes to the attendee's participation status in the organizer's calendar. Versions up to and including 10.1.21 are affected.
CVSS v3.1
Score 5.3medium
Affected software
Zimbra
Zimbra Collaboration Suite
pkg:github/zimbra/zimbra-collaboration-suiteRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability arises because Zimbra Collaboration Suite (ZCS) passes a null sender identity when processing iCalendar REPLY components, which causes the attendee authorization filter to be bypassed. An attacker who knows the meeting UID, organizer address, and attendee address can send a forged reply that updates the attendee's participation status without any interaction from the organizer or attendee. The affected versions include all releases up to 10.1.21 inclusive.
Potential Impact
The vulnerability allows an unauthenticated attacker to modify an attendee's participation status in a meeting on the organizer's calendar without authorization. This could lead to misinformation about meeting attendance but does not impact confidentiality or availability. The CVSS score is 5.3 (medium severity), reflecting limited impact on integrity only.
Mitigation Recommendations
No patch or official fix information is provided in the available data. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, organizations should be aware of this risk and consider monitoring for suspicious calendar activity or restricting calendar reply processing if possible.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- rapid7
- Date Reserved
- 2026-09-18T12:22:34.911Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6adb61954d27ba8daa2c43b6
Added to database: 10/23/2026, 13:31:01 UTC
Last enriched: 10/23/2026, 13:45:49 UTC
Last updated: 10/23/2026, 13:46:03 UTC
Views: 6
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