CVE-2019-6981 in Zimbra Collaboration Suite
Summary
by MITRE
Zimbra Collaboration Suite 8.7.x through 8.8.11 allows Blind SSRF in the Feed component.
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Analysis
by VulDB Data Team • 07/12/2025
The vulnerability identified as CVE-2019-6981 affects the Zimbra Collaboration Suite version 8.7.x through 8.8.11, specifically within the Feed component that handles external content aggregation. This represents a critical security flaw that enables attackers to perform blind server-side request forgery attacks, allowing unauthorized access to internal network resources that would otherwise be protected by firewalls and network segmentation. The vulnerability stems from insufficient input validation and sanitization in the feed parsing functionality, which processes external RSS and Atom feeds without proper restrictions on the URLs or endpoints that can be accessed.
The technical implementation of this vulnerability involves the Feed component's failure to properly validate and sanitize user-supplied URLs when processing external feed content. When a user subscribes to a malicious feed or when the system automatically processes feeds from untrusted sources, the application performs server-side requests to retrieve feed data without adequate filtering of destination URLs. This blind SSRF condition allows attackers to make requests to internal services, bypassing normal network security controls that would typically prevent external access to internal resources. The attack operates in a blind mode where the attacker cannot directly observe the responses from internal systems, but can infer information through timing attacks or by crafting payloads that trigger specific behaviors in target services.
The operational impact of this vulnerability is significant as it provides attackers with the ability to probe internal network infrastructure, potentially exposing sensitive services, databases, or administrative interfaces that should remain isolated from external access. Attackers can leverage this vulnerability to perform reconnaissance activities, identify internal services, and potentially escalate privileges by targeting weakly configured internal systems. The blind nature of the attack means that even if direct data exfiltration is not immediately possible, the ability to probe internal systems creates opportunities for further exploitation, including potential access to internal APIs, database connections, or other services that may not be properly secured. This vulnerability particularly affects organizations that rely on Zimbra for email services and may have complex internal network architectures where feed aggregation is enabled.
Organizations should implement multiple layers of mitigation strategies to address this vulnerability effectively. The primary recommendation involves upgrading to Zimbra Collaboration Suite version 8.8.12 or later, which contains patches specifically addressing the feed component validation issues. Additionally, network segmentation should be enforced to limit access to internal services from the Zimbra servers, implementing strict firewall rules that prevent outbound connections to internal resources from the feed processing components. Input validation should be strengthened through the implementation of allowlists for URL patterns, ensuring that only trusted domains can be accessed during feed processing operations. Organizations should also consider disabling feed aggregation features if they are not essential to business operations, and implement monitoring solutions that can detect unusual outbound network activity from their Zimbra servers. This vulnerability aligns with CWE-918, which describes server-side request forgery, and maps to ATT&CK technique T1071.004 for application layer protocol usage in command and control communications. The threat actor's ability to perform blind SSRF attacks represents a sophisticated approach to internal network reconnaissance and privilege escalation, making this vulnerability particularly dangerous in enterprise environments where internal resources are not adequately protected from lateral movement attacks.