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July 19, 2023

How to Patch a Critical XSS Vulnerability in Zimbra Collaboration Suite?

How To Patch A Critical Xss Vulnerability In Zimbra Collaboration Suite

Security researcher, Maddie Stone from Google Threat Analysis Group (TAG) uncover a new vulnerability in Zimbra Collaboration Suite. This is a critical (Cross Site Scripting) XSS vulnerability that could potentially impact the confidentiality and integrity of your data, it is important to Patch the Vulnerability at the earliest. We have created this post to let you know how to fix the Critical XSS Vulnerability in Zimbra Collaboration Suite.

A Short Note About the XSS Vulnerability

In short, Cross-Site Scripting (XSS) is a common security vulnerability typically found in web applications. This vulnerability allows attackers to inject malicious scripts into web pages viewed by other users. It occurs when an application includes untrusted data in a new web page without proper validation or escaping. XSS attacks can lead to a range of problems including identity theft, data theft, and defacement of websites, among others.

Introduction to the Zimbra Collaboration Suite

Zimbra Collaboration Suite (ZCS) is a collaborative software suite that includes an email server and a web client. Developed by Zimbra, Inc., a division of Synacor, it’s an open-source solution providing enterprise-class email, calendar, and collaboration capabilities.

ZCS is available in two editions: an open-source version, which is free, and a commercially supported version known as Network Edition. The latter offers additional features, such as support for push email, and synchronization with mobile devices.

The following table outlines the key differences between the two editions:

FeatureNetwork EditionOpen Source Edition
Paid supportYesNo
Premium email and collaboration featuresYesNo
Zimbra Connector for OutlookYesNo
Zimbra Mobile syncYesNo
Zimbra DesktopYesNo
Migration tools and servicesYesNo
24×7 phone and email supportYesNo

Key features of the Zimbra Collaboration Suite include:

  1. Email: Zimbra provides a full-featured email system with features such as spam and virus protection, attachment and message search, and the ability to handle large volumes of email.

  2. Calendar: The suite includes a group calendar for scheduling, with features for creating, accepting, or declining meeting invitations.

  3. Contacts: Users can maintain and share contacts. This feature also includes the ability to import and export contact lists in multiple formats.

  4. Document Storage and Sharing: Users can save and share documents within the system, which can be particularly useful for team collaboration.

  5. Task Management: Zimbra has a task management system that allows users to create tasks, set due dates, and assign tasks to others.

  6. Web Client: Zimbra offers a fully-featured web client that provides access to all the above features via a web browser. This allows users to access their email, calendar, contacts, documents, and tasks from any location.

  7. Integration and Compatibility: Zimbra is compatible with existing desktop email clients, such as Microsoft Outlook and Apple Mail. It can integrate with other systems using APIs and various protocols, including IMAP/POP, CalDAV, and CardDAV.

Zimbra is designed to be deployed in both on-premise and cloud environments, and it offers flexible deployment options to meet various business needs. Its feature-rich, collaborative capabilities and flexible deployment options make it a popular choice among businesses of all sizes.

Affected Zimbra Versions

As per the advisory, the flaw affects Zimbra Collaboration Suite Version 8.8.15. It is advised to go for a manual patching process until the official patches are rolled out at the time of the July patch release.

How to Patch a Critical XSS Vulnerability in the Zimbra Collaboration Suite?

Since the official patch is going to be shipped with July’s patch release. It is not recommended to wait until the release of the official patch as Google Threat Analysis Group (TAG) is alarmed that this flaw is being exploited in the wild. So users are urged to go for a manual fix to lower the attack surface. The vendor said that the flaw can be fixed by implementing input sanitation. You just need to follow this simple procedure to fix the Critical XSS Vulnerability in the Zimbra Collaboration Suite.

How to Manually Apply the Fix Across Your Mailbox Nodes?

Before we begin, it’s important to ensure that you have a backup of the file /opt/zimbra/jetty/webapps/zimbra/m/momoveto.
Steps to Safeguard Your Mailbox Nodes:

  1. Creating a Backup

    Start by taking a backup of the / opt/zimbra/jetty/webapps/zimbra/m/momoveto file. This acts as your safety net in case of any unforeseen issues.

  2. Update the Value

    Open the file in your favorite text editor and proceed to line number 40. Updating the Parameter Value as shone below.
    Existing value before you perform the update, the line will look like this:

    <input name="st" type="hidden" value="${}"/>

    You need to replace the value as shown below.

    <input name="st" type="hidden" value="${fn:escapeXml(}"/>

    Once you have successfully implemented the fix, the line will appear as follows:

    <input name="st" type="hidden" value="${fn:escapeXml(}"/>

    This simple change in the code adds an extra layer of protection to your mailbox nodes, securing them from potential threats.

No Need for a Service Restart

One of the best aspects of this fix is that a restart of the Zimbra service isn’t necessary. This means you can execute this fix without any interruption to your services or downtime, ensuring smooth operations while you bolster your defenses.

In conclusion, taking immediate action to protect your data is not only a smart choice but a necessary one. We urge you to manually apply this fix to all your mailbox nodes, taking a definitive step toward robust data security. Remember, your data is invaluable; treat it as such.

We hope this post helped you know how to patch the Critical XSS Vulnerability in Zimbra Collaboration Suite. Please share this post and help secure the digital world. Visit our website,, and our social media page on FacebookLinkedInTwitterTelegramTumblrMedium, and Instagram and subscribe to receive updates like this.  

Arun KL

Arun KL is a cybersecurity professional with 15+ years of experience in IT infrastructure, cloud security, vulnerability management, Penetration Testing, security operations, and incident response. He is adept at designing and implementing robust security solutions to safeguard systems and data. Arun holds multiple industry certifications including CCNA, CCNA Security, RHCE, CEH, and AWS Security.

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