CVE-2021-42091 in Zammad
Summary
by MITRE • 10/08/2021
An issue was discovered in Zammad before 4.1.1. SSRF can occur via GitHub or GitLab integration.
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Analysis
by VulDB Data Team • 10/14/2021
The vulnerability identified as CVE-2021-42091 represents a server-side request forgery flaw within the Zammad helpdesk system prior to version 4.1.1. This issue specifically manifests through the system's integration capabilities with external platforms including GitHub and GitLab. The vulnerability stems from insufficient input validation and sanitization mechanisms within the integration pathways that allow malicious actors to manipulate request parameters and potentially access internal systems or resources that should remain protected. Such vulnerabilities fall under the broader category of CWE-918 Server-Side Request Forgery, which is classified as a critical security weakness in web applications that permit remote attackers to make requests to internal services through vulnerable endpoints.
The technical exploitation of this vulnerability occurs when Zammad's integration modules handle requests from GitHub or GitLab services without proper validation of the target URLs or endpoints. Attackers can craft malicious requests that redirect the system's internal HTTP client to access arbitrary internal network resources, potentially including internal APIs, databases, or other sensitive systems. The flaw essentially allows an attacker to bypass normal network segmentation controls and gain unauthorized access to internal services that would typically be protected by firewalls or other network security measures. This type of attack vector is particularly dangerous because it can be initiated through legitimate integration points, making it harder to detect and distinguish from normal system behavior.
The operational impact of this vulnerability extends beyond simple unauthorized access to potentially include data exfiltration, system compromise, and lateral movement within the network infrastructure. Organizations using Zammad versions prior to 4.1.1 face significant risk of internal system enumeration, where attackers can discover and map internal network services. The vulnerability can be leveraged to access sensitive information stored in internal databases or to perform actions through integrated services that may have elevated privileges. This aligns with ATT&CK technique T1071.004 Application Layer Protocol: DNS, as the exploitation may involve DNS resolution of internal services, and T1105 Command and Control: Remote File Copy, if attackers attempt to exfiltrate data through the compromised integration points.
Organizations should implement immediate mitigations including updating to Zammad version 4.1.1 or later, which contains the necessary patches to address this vulnerability. Network segmentation controls should be reinforced to limit access between internal services and the helpdesk system, while implementing strict firewall rules that prevent outbound connections from the Zammad instance to internal resources. Input validation should be enhanced at all integration endpoints to ensure that only properly formatted URLs and endpoints are accepted. Additionally, organizations should consider implementing web application firewalls to monitor and filter requests to integration modules, and conduct regular security assessments to identify similar vulnerabilities in other integrated systems. The remediation process should include thorough testing of the updated system to ensure that legitimate integration functionality remains operational while the security vulnerability is properly addressed.