CVE-2020-5195 in FTP Server
Summary
by MITRE
Reflected XSS through an IMG element in Cerberus FTP Server prior to versions 11.0.1 and 10.0.17 allows a remote attacker to execute arbitrary JavaScript or HTML via a crafted public folder URL. This occurs because of the folder_up.png IMG element not properly sanitizing user-inserted directory paths. The path modification must be done on a publicly shared folder for a remote attacker to insert arbitrary JavaScript or HTML. The vulnerability impacts anyone who clicks the malicious link crafted by the attacker.
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Analysis
by VulDB Data Team • 03/20/2024
The vulnerability identified as CVE-2020-5195 represents a critical reflected cross-site scripting flaw within Cerberus FTP Server software that affects versions prior to 11.0.1 and 10.0.17. This security weakness stems from improper input validation and sanitization mechanisms within the server's handling of directory paths in publicly accessible folders. The vulnerability specifically manifests through the folder_up.png IMG element which fails to adequately sanitize user-provided directory path data, creating an avenue for malicious code injection. The flaw operates as a reflected XSS attack because the malicious payload is reflected back to users through the server's response, making it particularly dangerous for web-based file sharing environments.
The technical implementation of this vulnerability involves the server's failure to properly escape or filter special characters within directory path parameters that are subsequently rendered in HTML output. When a user accesses a publicly shared folder containing a crafted directory path, the Cerberus FTP Server processes the user input without adequate sanitization, allowing attackers to inject malicious HTML or JavaScript code directly into the IMG element's src attribute or surrounding context. This occurs because the server treats the user-supplied path as trusted input without proper validation, adhering to CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') which classifies this as a classic XSS vulnerability. The attack vector requires that the malicious path be inserted into a publicly accessible folder, making the vulnerability exploitable through shared links distributed to victims.
The operational impact of CVE-2020-5195 extends beyond simple code execution as it enables attackers to perform various malicious activities including session hijacking, credential theft, and redirection to malicious websites. When victims click on the crafted malicious links, their browsers execute the injected JavaScript code within the context of the vulnerable FTP server's domain, potentially compromising user sessions and enabling persistent attacks. The vulnerability affects any user who accesses the maliciously crafted URL, making it particularly dangerous in environments where shared folders are commonly accessed by multiple users. According to ATT&CK framework, this vulnerability maps to T1059.007 - Command and Scripting Interpreter: JavaScript, as it allows for JavaScript code execution, and T1566.001 - Phishing: Spearphishing Attachment, since attackers can craft malicious URLs that appear legitimate to unsuspecting users. The reflected nature of the vulnerability means that the malicious code is not stored on the server but rather injected through the URL parameter, making it difficult to detect through traditional server-side logging mechanisms.
Mitigation strategies for CVE-2020-5195 require immediate implementation of proper input sanitization and output encoding mechanisms within the Cerberus FTP Server software. Organizations should upgrade to versions 11.0.1 or 10.0.17 which contain the necessary patches to address the XSS vulnerability. Additionally, administrators should implement proper access controls to limit public folder sharing, employ web application firewalls that can detect and block suspicious URL patterns, and conduct regular security assessments of shared resources. The vulnerability demonstrates the importance of input validation at multiple layers within web applications, as the failure to sanitize user-provided data in the IMG element's context created a direct pathway for malicious code execution. Security teams should also consider implementing Content Security Policy headers to further limit the execution of unauthorized scripts, and establish monitoring protocols to detect unusual access patterns in shared folder resources that might indicate exploitation attempts.