What is CVE-2026-93628?

CVE-2026-93628 is a medium-severity vulnerability in Zimbra Collaboration Suite, classified under Authentication Bypass by Spoofing. CVSS score: 5.3/10. Published 2026-10-23.

How severe is CVE-2026-93628?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Zimbra Collaboration Suite

CVE-2026-93628

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 An attacker who knows the meeting UID, organizer address and attendee address can send a non-outdated reply that changes the attendee's participation status in the organizer's calendar.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.

Published 2026-10-23 · last modified 2026-10-23.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Zimbra Collaboration Suite

Weakness classification (CWE)

CWE-290 — Authentication Bypass by Spoofing

References

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

Frequently asked questions

What is CVE-2026-93628?: CVE-2026-93628 is a medium-severity vulnerability in Zimbra Collaboration Suite, classified under Authentication Bypass by Spoofing. CVSS score: 5.3/10. Published 2026-10-23.
How severe is CVE-2026-93628?: Medium severity. CVSS v3 base score is 5.3 out of 10.