CVE-2020-12846 Explained : Impact and Mitigation

Zimbra before 8.8.15 Patch 10 and 9.x before 9.0.0 Patch 3 allows remote code execution via an avatar file. Learn more about this critical vulnerability and how to mitigate it.

Understanding CVE-2020-12846

What is CVE-2020-12846?

Zimbra versions prior to 8.8.15 Patch 10 and 9.x before 9.0.0 Patch 3 are vulnerable to remote code execution through an avatar file upload mechanism.

The Impact of CVE-2020-12846

The vulnerability allows an attacker to upload executable files in the Contact section of the mailbox, potentially leading to remote code execution.

Technical Details of CVE-2020-12846

Vulnerability Description

The flaw resides in the /service/upload servlet in the webmail subsystem, enabling users to upload malicious files disguised as avatar images.

Affected Systems and Versions

Zimbra versions before 8.8.15 Patch 10
Zimbra 9.x versions before 9.0.0 Patch 3

Exploitation Mechanism

Users can upload executable files (exe, sh, bat, jar) as avatar images for contacts.
Despite receiving a "Corrupt File" error, the file is stored locally in /opt/zimbra/data/tmp/upload/, allowing for potential remote execution.

Mitigation and Prevention

Immediate Steps to Take

Apply the latest patches provided by Zimbra to fix the vulnerability.
Educate users about safe file upload practices and the risks associated with uploading executable files.

Long-Term Security Practices

Regularly monitor and audit file uploads in Zimbra to detect any suspicious activities.
Implement file type restrictions for uploads to prevent the execution of malicious files.

Patching and Updates

Update Zimbra to version 8.8.15 Patch 10 or version 9.0.0 Patch 3 to address this vulnerability.