CVE-2020-21053 in FusionPBX
Summary
by MITRE • 05/21/2021
Cross Site Scriptiong (XSS) vulnerability exists in FusionPBX 4.5.7 allows remote malicious users to inject arbitrary web script or HTML via an unsanitized "query_string" variable in app\devices\device_imports.php.
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Analysis
by VulDB Data Team • 05/23/2021
The vulnerability identified as CVE-2020-21053 represents a critical cross site scripting flaw within the FusionPBX 4.5.7 telephony management platform. This issue resides in the device_imports.php application module where user-supplied input from the query_string parameter is not properly sanitized before being processed and displayed within the web interface. The vulnerability affects the device import functionality, which is commonly used by administrators to bulk add or update device configurations in the system.
From a technical perspective, this vulnerability manifests as a classic XSS attack vector where malicious actors can inject arbitrary JavaScript code or HTML payloads into the application's response. The flaw occurs because the application fails to implement proper input validation and output encoding mechanisms for the query_string variable. When the system processes this unsanitized input, it directly incorporates the malicious content into the HTML response without adequate sanitization, creating an opportunity for attackers to execute scripts in the context of authenticated users' browsers.
The operational impact of this vulnerability extends beyond simple script injection, as it can be exploited to perform various malicious activities including session hijacking, credential theft, and data exfiltration. An attacker could craft a malicious query string that, when processed by the vulnerable device_imports.php script, would execute malicious JavaScript code in the browser of any user who accesses the affected functionality. This could lead to unauthorized access to the FusionPBX administrative interface, modification of device configurations, or even complete system compromise if the attacker can escalate privileges through the compromised session.
The vulnerability aligns with CWE-79 which specifically addresses cross site scripting flaws in web applications. According to the MITRE ATT&CK framework, this issue would be categorized under T1059.007 for scripting and T1566 for social engineering techniques that leverage web-based attacks. The attack surface is particularly concerning given that FusionPBX is commonly used in enterprise environments where administrators frequently manage device imports for VoIP systems, making this a prime target for attackers seeking persistent access to communication infrastructure.
Mitigation strategies should include immediate implementation of input validation and output encoding for all user-supplied data, particularly in the device_imports.php module. The application should sanitize all query_string parameters before processing them, implementing proper HTML entity encoding and input validation routines. Organizations should also consider implementing Content Security Policy headers to limit script execution capabilities, and conduct thorough code reviews to identify similar unsanitized input vectors throughout the application. Additionally, network segmentation and access controls should be enforced to limit the potential impact of successful exploitation, while regular security updates and patches should be deployed to address this vulnerability in affected systems.