Zimbra — CraftedSignal Threat Feed

Operation GhostMail: Russian APT Exploiting Zimbra XSS to Target Ukraine Government

hello@craftedsignal.io — Fri, 20 Mar 2026 05:20:03 +0000

A Russian APT group is conducting a campaign, known as “Operation GhostMail,” targeting the Ukrainian government. The attackers are leveraging a cross-site scripting (XSS) vulnerability in Zimbra collaboration suite to gain unauthorized access. While the specific vulnerability (CVE) is not provided in the source material, the attackers are clearly focused on exploiting this weakness. The operation highlights the ongoing cyber conflict impacting Ukraine. Defenders need to focus on detecting exploitation attempts against Zimbra and anomalous activity originating from compromised email accounts. The scope of this campaign appears limited to the Ukrainian government sector.

Attack Chain

The attacker identifies a vulnerable Zimbra server within the Ukrainian government infrastructure.
The attacker crafts a malicious email containing a specially crafted XSS payload.
The victim receives the email and opens it within the Zimbra webmail client.
The XSS payload executes within the victim’s browser, allowing the attacker to steal the victim’s Zimbra session cookie.
The attacker uses the stolen session cookie to authenticate to the Zimbra webmail client as the victim.
The attacker gains access to the victim’s email account, contacts, and calendar.
The attacker uses the compromised email account to send further phishing emails to other targets within the Ukrainian government, escalating the attack.
The attacker exfiltrates sensitive information from the compromised mailboxes and possibly pivots to other internal systems.

Impact

This campaign is focused on espionage and potential disruption of Ukrainian government operations. Successful exploitation leads to unauthorized access to sensitive email communications, contact lists, and calendar information. Compromised email accounts can be used to spread further phishing attacks within the government, increasing the scope of the breach. The exfiltration of sensitive data can lead to reputational damage and compromise of national security.

Recommendation

Deploy the Sigma rule Detect Suspicious Zimbra Webmail Activity to your SIEM and tune for your environment to identify unusual actions within the Zimbra webmail interface.
Monitor network traffic for unusual connections originating from Zimbra servers, which can be indicative of post-exploitation activity, using the Detect Zimbra Server Outbound Connections Sigma rule.
Implement multi-factor authentication (MFA) for all Zimbra accounts to mitigate the impact of stolen credentials.
Conduct regular security audits of Zimbra installations to identify and patch any known vulnerabilities.

Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability

hello@craftedsignal.io — Wed, 24 Jan 2024 12:00:00 +0000

A cross-site scripting (XSS) vulnerability, identified as CVE-2025-48700, exists within the Synacor Zimbra Collaboration Suite (ZCS). This flaw could be exploited by attackers to inject and execute arbitrary JavaScript code within a user’s web browser session when they interact with a compromised Zimbra instance. Successful exploitation could lead to the theft of session cookies, credential harvesting, or other malicious activities performed on behalf of the victim user. The vulnerability requires user interaction to trigger, making it essential to educate users about the risks of clicking on untrusted links or opening suspicious attachments. The scope of the vulnerability affects installations of Zimbra Collaboration Suite.

Attack Chain

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