CVE-2016-4971 in wget
Summary
by MITRE
GNU wget before 1.18 allows remote servers to write to arbitrary files by redirecting a request from HTTP to a crafted FTP resource.
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Analysis
by VulDB Data Team • 12/01/2024
The vulnerability identified as CVE-2016-4971 represents a critical file system manipulation flaw within GNU wget version 1.18 and earlier. This issue stems from wget's handling of protocol redirects, specifically when transitioning from HTTP to FTP resources. The vulnerability allows remote attackers to manipulate the local file system by crafting malicious FTP URLs that wget will follow during redirects, potentially leading to arbitrary file creation or modification on the target system. This behavior violates fundamental security principles of file system access control and privilege separation, as the application executes operations that should be restricted to authorized users or processes.
The technical mechanism behind this vulnerability involves wget's automatic redirect handling functionality combined with its FTP protocol support. When wget encounters an HTTP redirect to an FTP resource, it processes the FTP URL without sufficient validation of the target file path. The flaw occurs because the application does not properly sanitize or validate the file path components of the redirected FTP URL, allowing attackers to specify absolute paths or directory traversal sequences that result in unintended file system operations. This vulnerability falls under the category of path traversal and file system manipulation attacks, with direct implications for file system integrity and access control mechanisms.
The operational impact of CVE-2016-4971 extends beyond simple file system manipulation to encompass potential privilege escalation and persistent threat capabilities. An attacker who controls a remote HTTP server can craft redirects that cause wget to write malicious files to system directories, potentially including system configuration files, binaries, or other sensitive locations. This vulnerability is particularly dangerous in automated environments where wget is used for downloading content, such as in package managers, automated deployment scripts, or security scanning tools. The vulnerability can be exploited across multiple attack vectors including web application vulnerabilities, compromised web servers, or man-in-the-middle scenarios where attackers can inject malicious redirects into HTTP responses.
Mitigation strategies for this vulnerability require immediate patching of wget to version 1.18 or later, which includes proper validation of file paths during FTP redirects. Organizations should also implement network-level controls such as firewall rules to restrict access to known vulnerable systems and monitor for unusual wget behavior. Additionally, system administrators should review and audit wget usage patterns, particularly in automated environments where the application may be processing untrusted input. The vulnerability demonstrates the importance of proper input validation and the principle of least privilege in security implementations, aligning with CWE-22 Path Traversal and ATT&CK technique T1059 Command and Scripting Interpreter. Security teams should also consider implementing application whitelisting policies and monitoring for suspicious file system operations that may indicate exploitation attempts.