What is CVE-2026-93638?

CVE-2026-93638 is a medium-severity vulnerability in Zimbra Collaboration Suite, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-10-23.

How severe is CVE-2026-93638?

Medium severity. CVSS v3 base score is 6.1 out of 10.

XSS in Zimbra Collaboration Suite

CVE-2026-93638

A reflected cross-site scripting vulnerability in the login page of Zimbra Collaboration Suite (ZCS) allows an unauthenticated attacker to execute JavaScript through the zrememberme parameter. A crafted relogin URL selects a two-factor error display that inserts the parameter into a hidden input attribute without HTML encoding. A victim who opens the URL receives attacker-controlled script and page content under the legitimate Zimbra origin, allowing credential capture through a replacement login form. The relogin path logs out an existing session before rendering the payload, so the demonstrated attack does not inherit that session's mailbox access. ZCS 10.1.16 and 10.1.17 are affected.

Vulnerability class: XSS (Cross-Site Scripting)

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

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/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-79 — Cross-site Scripting

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-2026-93638?: CVE-2026-93638 is a medium-severity vulnerability in Zimbra Collaboration Suite, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-10-23.
How severe is CVE-2026-93638?: Medium severity. CVSS v3 base score is 6.1 out of 10.