CVE-2016-6839 in FusionAccess
Summary
by MITRE
CRLF injection vulnerability in Huawei FusionAccess before V100R006C00 allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via unspecified vectors.
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Analysis
by VulDB Data Team • 09/15/2022
The CVE-2016-6839 vulnerability represents a critical CRLF injection flaw discovered in Huawei FusionAccess software prior to version V100R006C00. This vulnerability falls under the CWE-113 category, which specifically addresses improper neutralization of CRLF characters within HTTP headers, making it a direct descendant of the well-known HTTP response splitting attack vector. The flaw enables remote attackers to manipulate HTTP responses by injecting carriage return line feed sequences that can alter the structure of HTTP headers, potentially allowing for malicious redirection, session hijacking, or cross-site scripting attacks.
The technical implementation of this vulnerability occurs within the web application layer of Huawei FusionAccess, where user-supplied input is not properly sanitized before being incorporated into HTTP response headers. Attackers can exploit this weakness by crafting malicious requests that contain CRLF sequences in parameters or input fields, which then get processed and embedded into HTTP headers without adequate validation or encoding. This injection mechanism allows adversaries to inject arbitrary HTTP headers into the response stream, effectively splitting the HTTP response and enabling them to inject additional headers that can be used to redirect users to malicious sites or manipulate browser behavior.
The operational impact of CVE-2016-6839 extends beyond simple header injection, as it provides attackers with the capability to perform HTTP response splitting attacks that can lead to various security breaches. When successfully exploited, this vulnerability can enable man-in-the-middle attacks where attackers can manipulate the content of web responses, inject malicious content, or redirect users to phishing sites. The vulnerability is particularly dangerous in enterprise environments where FusionAccess is used for virtual desktop infrastructure, as it could allow attackers to compromise user sessions and gain unauthorized access to sensitive corporate resources. The attack surface is broad since the vulnerability affects multiple vectors within the application's input handling mechanisms, making it difficult to fully mitigate without comprehensive patching.
Organizations affected by this vulnerability should prioritize immediate remediation through the application of Huawei's official security patches released for version V100R006C00 and subsequent releases. The mitigation strategy should include implementing proper input validation and sanitization mechanisms at all entry points where user data is processed, particularly in areas handling HTTP headers or response construction. Network segmentation and monitoring solutions should be deployed to detect anomalous HTTP response patterns that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to T1190 (Exploit Public-Facing Application) and T1071.004 (Application Layer Protocol: DNS) as attackers can leverage the injected headers to redirect traffic or establish malicious domains. Additionally, organizations should consider implementing web application firewalls to detect and block CRLF injection attempts, while also conducting regular security assessments to identify similar vulnerabilities in other components of their infrastructure. The vulnerability serves as a reminder of the critical importance of proper input validation and output encoding in preventing HTTP response splitting attacks, which remain a persistent threat in web application security.