Hackers Exploiting Zimbra 0-day to Attack Government Organizations

Zimbra Collaboration is an open-source solution software suite with an email server and web client for collaboration. 

Over 5,000 companies and public sector users, along with hundreds of millions of end-users in more than 140 countries, utilize this solution.

Google TAG (Threat Analysis Group) found an in-the-wild 0-day exploit in June 2023 targeting Zimbra Collaboration (CVE-2023-37580). 

In total, there are four distinct groups that exploited this bug, stealing the following data:-

  • Email data
  • User credentials
  • Authentication tokens

Flaw Profile

  • CVE ID: CVE-2023-37580
  • Description: Zimbra Collaboration (ZCS) 8 before 8.8.15 Patch 41 allows XSS in the Zimbra Classic Web Client.
  • Base Score: 6.1 
  • Severity: MEDIUM
  • Vulnerability Name: Required Action Zimbra Collaboration (ZCS) Cross-Site Scripting (XSS) Vulnerability.

Hackers Exploiting Zimbra 0-day

Most of the activity took place after the initial fix went public on GitHub. TAG highlights staying protected by keeping software up-to-date and promptly applying security updates.

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TAG found a critical XSS flaw in Zimbra’s email server (CVE-2023-37580), which was actively exploited in June. Zimbra released a hotfix on July 5, 2023, and an advisory on July 13, 2023.

Timeline (Source – Google TAG)

Besides this, researchers also identified three threat groups exploiting it before the official patch, and a fourth campaign emerged after the fix.

Zimbra’s URL vulnerability led to a reflected XSS, allowing the injection of malicious scripts into web pages.


Here below we have mentioned all the campaigns:-

  • Campaign 1: First known exploitation leads to email-stealing framework
  • Campaign 2: Winter Vivern exploitation after hotfix pushed to Github
  • Campaign 3: Exploit used for credential phishing
  • Campaign 4: N-day exploit used for stealing authentication token

The discovery of four CVE-2023-37580 campaigns underscores the urgency for prompt mail server fixes. Attackers exploit vulnerabilities post-Github fix, pre-public advisory. 

This follows CVE-2022-24682 exploitation and precedes CVE-2023-5631. Regular XSS exploits highlight the need for rigorous mail server code audits.


  • https://obsorth.opwtjnpoc[.]ml/pQyMSCXWyBWJpIos.js
  • https://applicationdevsoc[.]com/zimbraMalwareDefender/zimbraDefender.js
  • https://applicationdevsoc[.]com/tndgt/auth.js
  • ntcpk[.]org

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Tushar is a Cyber security content editor with a passion for creating captivating and informative content. With years of experience under his belt in Cyber Security, he is covering Cyber Security News, technology and other news.