CVE-2016-4802 in cURL
Summary
by MITRE
Multiple untrusted search path vulnerabilities in cURL and libcurl before 7.49.1, when built with SSPI or telnet is enabled, allow local users to execute arbitrary code and conduct DLL hijacking attacks via a Trojan horse (1) security.dll, (2) secur32.dll, or (3) ws2_32.dll in the application or current working directory.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2016-4802 represents a critical untrusted search path issue affecting cURL and libcurl versions prior to 7.49.1. This flaw specifically manifests when the applications are compiled with SSPI (Security Support Provider Interface) or telnet support enabled, creating a dangerous condition where malicious actors can exploit the application's dynamic library loading mechanism to execute arbitrary code. The vulnerability stems from the improper handling of library search paths, where cURL and libcurl fail to properly validate the source of dynamically loaded libraries, allowing attackers to place malicious DLL files in directories that are searched before the legitimate system directories.
The technical exploitation of this vulnerability relies on the Windows dynamic linking mechanism and the specific conditions present in the cURL build configuration. When cURL or libcurl is compiled with SSPI support, it attempts to load security-related DLLs such as security.dll, secur32.dll, or ws2_32.dll during operation. The flaw occurs because these applications do not implement secure library loading practices, particularly when the current working directory is placed ahead of system directories in the search order. This creates a window where an attacker can place a malicious DLL with the same name as a legitimate system DLL in the application's directory or current working directory, causing the application to load and execute the attacker-controlled code instead of the legitimate system library.
From an operational impact perspective, this vulnerability enables local privilege escalation and arbitrary code execution with the privileges of the user running the vulnerable cURL or libcurl application. The attack vector is particularly insidious because it requires minimal user interaction beyond the execution of the vulnerable application, making it a significant concern for environments where cURL is used extensively. The vulnerability affects not just standalone applications but also systems that depend on libcurl for network operations, potentially allowing attackers to compromise web applications, automated scripts, or system utilities that utilize cURL for HTTP operations. This represents a classic DLL hijacking attack pattern that aligns with attack techniques documented in the MITRE ATT&CK framework under the T1056.001 sub-technique for "Input Injection" and T1068 for "Exploitation for Privilege Escalation".
The security implications extend beyond simple code execution to encompass potential system compromise and data exfiltration capabilities. When an attacker successfully places a malicious DLL in the search path, they can potentially execute code with the privileges of the target process, which could range from standard user privileges to system-level access depending on how the vulnerable application is executed. This vulnerability particularly affects enterprise environments where cURL is used in automated processes, web scraping applications, or network monitoring tools, as these applications may run with elevated privileges. The vulnerability's classification under CWE-427 indicates a weakness in the application's handling of untrusted search paths, which represents a fundamental flaw in secure coding practices and proper library loading mechanisms.
Mitigation strategies for CVE-2016-4802 primarily focus on updating to cURL version 7.49.1 or later, which implements proper library loading mechanisms that avoid the insecure search path behavior. Organizations should also implement application whitelisting policies to restrict which DLLs can be loaded by vulnerable applications, and ensure that system directories are prioritized over user directories in the library search order. Additionally, security teams should monitor for the presence of vulnerable cURL installations in their environment and conduct regular vulnerability assessments to identify and remediate similar issues. The implementation of secure coding practices, including proper DLL loading techniques and validation of library sources, should be enforced across all development teams to prevent similar vulnerabilities from being introduced in future applications. This vulnerability serves as a reminder of the importance of secure library loading practices and proper input validation in preventing privilege escalation attacks.