CVE-2026-93647 Cross-site scripting in Zimbra Collaboration Suite (ZCS)
An unauthenticated attacker can inject malicious scripts into calendar messages, allowing them to steal mailbox data and hijack user sessions in Zimbra.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-93647?
CVE-2026-93647 is a critical cross-site scripting vulnerability in Zimbra Collaboration Suite (ZCS), published on 25 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
An unauthenticated calendar sender can place active markup in a COUNTER message's RFC From address. Selecting the message in Zimbra Classic triggers stored XSS, allowing the attacker to access mailbox data and act as the victim.
Weakness: CWE-79
Which versions are affected by CVE-2026-93647?
How do I fix CVE-2026-93647?
No fix has been published for CVE-2026-93647 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-93647 being exploited?
There is no known exploitation of CVE-2026-93647 in the wild and no public exploit code.
Sources
Also known as GHSA-h5jf-rfhh-rx8c.