CISA Issues Alert Over Actively Exploited Flaw in Zimbra Collaboration Suite

The Cybersecurity and Infrastructure Security Agency (CISA) has issued a critical alert regarding an actively exploited vulnerability in Synacor’s Zimbra Collaboration Suite (ZCS), urging organizations to take immediate action to mitigate the threat.

The flaw, tracked as CVE-2019-9621, is a server-side request forgery (SSRF) vulnerability that resides in the ProxyServlet component of ZCS and has been added to CISA’s Known Exploited Vulnerabilities (KEV) catalog as of July 7, 2025.

What Is the Vulnerability?

CVE-2019-9621 allows remote attackers to exploit the ProxyServlet component in certain versions of Zimbra Collaboration Suite.

By leveraging this SSRF flaw, threat actors can force the server to make unauthorized requests to internal or external resources, potentially leading to remote code execution, data exfiltration, or further compromise of the affected system.

The vulnerability is classified as extremely high risk due to its potential impact and evidence of active exploitation in the wild.

Affected Versions

The vulnerability impacts multiple versions of Zimbra Collaboration Suite, including:

• ZCS up to and excluding 8.6.0
• ZCS from 8.7.0 up to and excluding 8.7.11
• ZCS from 8.8.0 up to and excluding 8.8.10

According to recent reports, CVE-2019-9621 is being actively exploited by threat actors, with some evidence linking exploitation attempts to sophisticated groups.

While it remains unclear whether this vulnerability has been leveraged specifically in ransomware campaigns, the high-profile nature of the flaw and its ease of exploitation have raised alarms across the cybersecurity community.

The SSRF vulnerability enables attackers to bypass security controls, access sensitive internal services, or even execute arbitrary code on vulnerable servers.

This could lead to widespread disruption, data breaches, and unauthorized access to critical business communications.

CISA has mandated that all federal agencies and strongly encourages private sector organizations to:

• Apply vendor-issued patches and mitigations for Zimbra Collaboration Suite immediately.
• Follow BOD 22-01 guidance for cloud services to ensure compliance and reduce exposure.
• Discontinue use of the product if mitigations or patches are unavailable before the due date of July 28, 2025.

Failure to address this vulnerability could result in significant security incidents, including data loss and operational disruption.

CISA’s alert underscores the urgent need for vigilance and rapid response in the face of evolving cyber threats.

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