CVE-2014-8517 in Mac OS X
Summary
by MITRE
The fetch_url function in usr.bin/ftp/fetch.c in tnftp, as used in NetBSD 5.1 through 5.1.4, 5.2 through 5.2.2, 6.0 through 6.0.6, and 6.1 through 6.1.5 allows remote attackers to execute arbitrary commands via a | (pipe) character at the end of an HTTP redirect.
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Analysis
by VulDB Data Team • 12/09/2024
The vulnerability identified as CVE-2014-8517 affects the tnftp client software distributed with NetBSD operating systems across multiple versions including 5.1 through 5.1.4, 5.2 through 5.2.2, 6.0 through 6.0.6, and 6.1 through 6.1.5. This represents a critical security flaw in the fetch_url function located within the usr.bin/ftp/fetch.c source file that governs how the ftp client handles HTTP redirects. The vulnerability stems from insufficient input validation and sanitization mechanisms that fail to properly handle special characters in redirect URLs, creating a command injection vector that can be exploited by remote attackers. The flaw specifically manifests when a malicious HTTP redirect contains a pipe character | at the end of the URL, which the tnftp client interprets as a command separator rather than a literal character in the URL path.
The technical exploitation of this vulnerability occurs through the manipulation of HTTP redirect responses that contain a pipe character as the final character in the redirect location header. When tnftp encounters such a redirect, it processes the URL without proper sanitization, allowing the pipe character to be interpreted as a shell command separator. This creates a dangerous situation where an attacker can inject arbitrary shell commands that get executed with the privileges of the tnftp process, which typically runs with the permissions of the user initiating the ftp session. The vulnerability falls under CWE-78, which specifically addresses OS Command Injection, and represents a classic example of improper input validation that allows attackers to bypass normal execution flow and execute unauthorized commands on the target system.
The operational impact of CVE-2014-8517 extends beyond simple command execution, as it can enable attackers to perform a wide range of malicious activities including but not limited to data exfiltration, system enumeration, privilege escalation, and persistent access establishment. Attackers can leverage this vulnerability to gain unauthorized access to systems that use tnftp for file transfers, potentially compromising entire networks if the affected systems are part of larger infrastructure. The vulnerability is particularly concerning because it can be exploited remotely without requiring authentication, making it an attractive target for automated attacks. From an ATT&CK framework perspective, this vulnerability maps to multiple techniques including T1059.004 for Unix shell commands and T1078 for valid accounts, as the attack can be executed using legitimate user accounts while exploiting the command injection flaw to extend privileges and maintain access.
Mitigation strategies for CVE-2014-8517 involve immediate patching of affected NetBSD systems with the latest security updates that address the command injection vulnerability in the fetch_url function. Organizations should also implement network-level controls such as firewall rules that restrict access to external HTTP services that might be used to deliver malicious redirects, and deploy intrusion detection systems that can identify suspicious HTTP redirect patterns. Additionally, administrators should consider disabling the tnftp utility if it is not essential for operations, or at minimum configure it to only accept redirects from trusted sources. The vulnerability demonstrates the importance of proper input validation and sanitization in network applications, particularly those that process external data such as HTTP headers and redirect URLs, and serves as a reminder that even seemingly benign network utilities can contain critical security flaws that can be exploited for remote code execution.