CVE-2017-15646 in Webmin
Summary
by MITRE
Webmin before 1.860 has XSS with resultant remote code execution. Under the 'Others/File Manager' menu, there is a 'Download from remote URL' option to download a file from a remote server. After setting up a malicious server, one can wait for a file download request and then send an XSS payload that will lead to Remote Code Execution, as demonstrated by an OS command in the value attribute of a name='cmd' input element.
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Analysis
by VulDB Data Team • 07/07/2024
The vulnerability described in CVE-2017-15646 represents a critical security flaw in Webmin versions prior to 1.860 that demonstrates the dangerous intersection of cross-site scripting and remote code execution capabilities. This vulnerability specifically resides within the File Manager module's 'Download from remote URL' functionality, which creates a pathway for attackers to execute malicious code on affected systems. The flaw operates through a sophisticated chain of exploitation where an attacker first sets up a malicious server to intercept file download requests, then injects malicious payloads that exploit the XSS vulnerability to ultimately achieve remote code execution. The vulnerability manifests when an attacker crafts a specially designed payload that includes an OS command within the value attribute of a name='cmd' input element, effectively allowing arbitrary command execution on the target system.
The technical nature of this vulnerability aligns with CWE-79 Cross-site Scripting and CWE-78 Command Injection, demonstrating how seemingly disparate vulnerabilities can combine to create more severe security risks. The attack vector exploits the trust relationship between the Webmin interface and its underlying file handling processes, where user-supplied data from remote URL downloads is not properly sanitized or validated before being processed. This allows attackers to inject malicious JavaScript code that executes within the context of the victim's browser session, which then leverages the existing file download functionality to execute arbitrary commands on the server. The vulnerability's impact is particularly severe because it enables attackers to bypass traditional security controls and directly manipulate the system's command execution capabilities through a relatively simple injection attack.
From an operational perspective, this vulnerability poses significant risks to organizations using affected Webmin versions, as it allows attackers to gain full administrative control over the affected systems. The exploitation process requires minimal technical expertise and can be automated, making it particularly dangerous for widespread deployment. The remote code execution capability means that attackers can install backdoors, exfiltrate data, modify system configurations, or perform other malicious activities without detection. The vulnerability's presence in the File Manager module makes it particularly insidious since this functionality is commonly used for legitimate file management tasks, making the malicious activity harder to distinguish from normal operations. Organizations with Webmin installations are particularly vulnerable during peak usage periods when legitimate file download requests are frequent, as attackers can exploit the timing to maximize their chances of successful exploitation.
Mitigation strategies for CVE-2017-15646 primarily focus on immediate patching of affected Webmin installations to version 1.860 or later, which contains the necessary security fixes to prevent the XSS and subsequent RCE exploitation. Organizations should also implement network-level controls such as web application firewalls that can detect and block malicious payloads targeting this specific vulnerability pattern. Additional defensive measures include restricting access to the Webmin interface through network segmentation, implementing strict input validation for all user-supplied data, and conducting regular security audits of web applications. The vulnerability's characteristics also make it suitable for detection through behavioral monitoring systems that can identify unusual command execution patterns or unauthorized file download activities. Security teams should also consider implementing principle of least privilege access controls to limit the potential damage from successful exploitation, ensuring that even if an attacker gains access, their capabilities remain restricted. The vulnerability serves as a reminder of the importance of proper input validation and output encoding in web applications, particularly in administrative interfaces where elevated privileges are available.