CVE-2021-35209

9.8 criticalEPSS 3.0%

Critical (9.8) in zimbra collaboration. EPSS 3.0% chance of exploitation in the next 30 days.

An issue was discovered in ProxyServlet.java in the /proxy servlet in Zimbra Collaboration Suite 8.8 before 8.8.15 Patch 23 and 9.x before 9.0.0 Patch 16. The value of the X-Host header overwrites the value of the Host header in proxied requests. The value of X-Host header is not checked against the whitelist of hosts Zimbra is allowed to proxy to (the zimbraProxyAllowedDomains setting).

Severity

CVSS 3.1

9.8 critical

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

EPSS: 3.0% chance of exploitation in the next 30 days; higher than 87% of CVEs (scores of 2026-10-31)
CWE: CWE-918
Published: 2021-07-02
Modified: 2026-06-17
Record from: the NVD, synced 2026-10-19

Affected

zimbra:collaboration

References

https://blog.sonarsource.com/zimbra-webmail-compromise-via-email
https://wiki.zimbra.com/wiki/Security_Center
https://wiki.zimbra.com/wiki/Zimbra_Releases/8.8.15/P23
https://wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P16
https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories

Check your stack JSON