CVE-2020-5889 in BIG-IP APM
Summary
by MITRE
On versions 15.1.0-15.1.0.1, 15.0.0-15.0.1.2, and 14.1.0-14.1.2.3, in BIG-IP APM portal access, a specially crafted HTTP request can lead to reflected XSS after the BIG-IP APM system rewrites the HTTP response from the untrusted backend server and sends it to the client.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 10/14/2020
The vulnerability identified as CVE-2020-5889 represents a critical reflected cross-site scripting flaw within F5 BIG-IP APM portal access functionality. This security weakness affects multiple versions of the F5 BIG-IP system including 15.1.0-15.1.0.1, 15.0.0-15.0.1.2, and 14.1.0-14.1.2.3, exposing organizations to significant web application security risks. The flaw occurs specifically within the APM (Application Policy Manager) module's handling of HTTP responses from backend servers, creating an avenue for malicious actors to inject and execute arbitrary script code in the context of victim users' browsers.
The technical mechanism of this vulnerability involves the BIG-IP APM system's process of rewriting HTTP responses from untrusted backend servers before forwarding them to clients. When a specially crafted HTTP request is submitted to the system, the APM module processes this request and subsequently rewrites the response headers or content. During this rewriting process, the system fails to properly sanitize or escape user-controllable input parameters that are subsequently reflected back to the client browser. This inadequate input validation and output encoding creates an environment where malicious script code can be embedded within the HTTP response and executed when the victim's browser renders the page, leading to potential session hijacking, credential theft, or other malicious activities.
The operational impact of CVE-2020-5889 extends beyond simple script execution, as it can enable attackers to perform sophisticated attacks against authenticated users within the APM portal environment. This vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and represents a direct violation of secure coding practices for input validation and output encoding. The reflected nature of this XSS vulnerability means that attackers do not need to store malicious code on the target system, as the malicious payload is delivered through the HTTP request itself and immediately reflected back to the user's browser. This characteristic makes the vulnerability particularly dangerous in environments where users may be tricked into clicking malicious links or where automated attacks can be launched through various vectors.
Organizations utilizing affected BIG-IP versions should implement immediate mitigations including applying the latest security patches provided by F5, implementing web application firewalls to filter malicious requests, and conducting thorough security assessments of their APM portal configurations. The vulnerability also maps to ATT&CK technique T1059.007 for command and scripting interpreter, specifically in the context of script injection attacks. Additional defensive measures should include implementing Content Security Policy headers, enabling proper input validation at all entry points, and conducting regular security testing of web applications to identify similar vulnerabilities. Organizations should also consider network segmentation to limit the potential impact of successful exploitation and maintain comprehensive monitoring of their APM systems for suspicious activity. The vulnerability demonstrates the critical importance of proper input sanitization and output encoding in web applications, particularly in enterprise security products that handle sensitive user data and authentication flows.