CVE-2021-35209

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).

• CWE-918

• https://blog.sonarsource.com/zimbra-webmail-compromise-via-emailExploit, Third Party Advisory
• https://wiki.zimbra.com/wiki/Security_CenterRelease Notes, Vendor Advisory
• https://wiki.zimbra.com/wiki/Zimbra_Releases/8.8.15/P23Release Notes, Vendor Advisory
• https://wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P16Release Notes, Vendor Advisory
• https://wiki.zimbra.com/wiki/Zimbra_Security_AdvisoriesVendor Advisory
• https://blog.sonarsource.com/zimbra-webmail-compromise-via-emailExploit, Third Party Advisory
• https://wiki.zimbra.com/wiki/Security_CenterRelease Notes, Vendor Advisory
• https://wiki.zimbra.com/wiki/Zimbra_Releases/8.8.15/P23Release Notes, Vendor Advisory
• https://wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P16Release Notes, Vendor Advisory
• https://wiki.zimbra.com/wiki/Zimbra_Security_AdvisoriesVendor Advisory

Published

Jul 2, 2021

Last Modified

Jun 17, 2026

Status

Modified

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