Attack Chain

1. Attacker identifies a vulnerable Zimbra Collaboration Suite (ZCS) instance.
2. Attacker crafts a malicious URL or injects malicious JavaScript into a ZCS component (e.g., email, calendar, or task).
3. The attacker delivers the malicious URL or crafted item to a target user, often via phishing or social engineering.
4. The user clicks on the malicious URL or interacts with the injected content within ZCS.
5. The user’s browser executes the attacker-controlled JavaScript code.
6. The JavaScript code steals the user’s session cookie or performs other malicious actions within the context of the user’s session.
7. The attacker uses the stolen session cookie to hijack the user’s session and gain unauthorized access to the Zimbra account.
8. The attacker accesses sensitive information, sends malicious emails, or performs other unauthorized actions on behalf of the compromised user.

Impact

Successful exploitation of this XSS vulnerability can lead to unauthorized access to sensitive information stored within the Zimbra Collaboration Suite. Attackers could potentially read emails, access contacts, steal credentials, and perform other malicious activities on behalf of the compromised user. This can result in data breaches, financial loss, and reputational damage. The number of potential victims depends on the number of users of the affected Zimbra instance.

Recommendation

• Apply mitigations per vendor instructions to patch CVE-2025-48700 (https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories).
• Follow applicable BOD 22-01 guidance for cloud services if Zimbra ZCS is deployed in a cloud environment.
• Deploy the Sigma rule “Detect Suspicious URI Parameters for Potential XSS” to identify potentially malicious requests targeting ZCS.
• Educate users about the risks of clicking on untrusted links and opening suspicious attachments to prevent exploitation of the XSS vulnerability.