Vulnerabilities / CVE-2026-93628

CVE-2026-93628

Published 2026-10-23 · published (not yet in NVD)

CVE-2026-93628

Zimbra Collaboration Suite Calendar Processing Authentication Bypass via Forged iCalendar REPLY Attendee Response

5.3 MEDIUM
CVSS 3.1 · CNA

0.3%
chance of exploitation in the next 30 days (EPSS; higher than 19% of CVEs)

An attendee authentication vulnerability in the email calendar processing of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to forge another attendee's response to an existing meeting. Zimbra passes a null sender identity when processing iCalendar REPLY components, causing the attendee authorization filter to be skipped. An attacker who knows the meeting UID, organizer address and attendee address can send a non-outdated reply that changes the attendee's participation status in the organizer's calendar. The change occurs automatically during delivery without organizer or attendee interaction. ZCS 10.1.16 and 10.1.21 are affected.

Scores

5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:NCNA

Affected products

Zimbra Zimbra Collaboration Suite: 0 to ≤ 10.1.21

Weakness: CWE-290

2 references (advisories, patches, write-ups)

https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories · vendor-advisory
https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/ · related

Sources: CVE.org, FIRST EPSS. Missing ones did not answer or have no record yet.

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