CVE-2015-3887 in ProxyChains-NG
Summary
by MITRE
Untrusted search path vulnerability in ProxyChains-NG before 4.9 allows local users to gain privileges via a Trojan horse libproxychains4.so library in the current working directory, which is referenced in the LD_PRELOAD path.
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Analysis
by VulDB Data Team • 12/29/2022
The vulnerability described in CVE-2015-3887 represents a critical untrusted search path issue affecting ProxyChains-NG versions prior to 4.9. This flaw resides in the library loading mechanism of the proxychains-ng tool, which is widely used for routing network connections through proxy servers. The vulnerability specifically targets the dynamic library loading process that occurs when the application executes, creating a pathway for privilege escalation through malicious library injection. The issue manifests when the system searches for required shared libraries in a predictable order that includes the current working directory, allowing an attacker to place a malicious library file in the same directory as the target application.
The technical exploitation of this vulnerability leverages the LD_PRELOAD environment variable mechanism, which is a standard Linux feature allowing applications to load specific shared libraries before others. When ProxyChains-NG executes, it searches for libproxychains4.so in the standard library paths including the current working directory. This search order vulnerability enables local attackers to place a malicious version of libproxychains4.so in the directory from which the application is executed. The malicious library can then be loaded in place of the legitimate one, potentially executing arbitrary code with the privileges of the target process. This represents a classic case of a library injection attack that exploits the trust placed in the application's library loading sequence, aligning with CWE-426, which addresses the execution of untrusted code due to insecure library loading practices.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass broader system compromise capabilities. Local users who can write to directories where ProxyChains-NG is executed gain the ability to execute code with elevated privileges, potentially leading to full system compromise if the application runs with higher privileges than the user. The attack vector is particularly concerning because it requires minimal privileges to exploit and can be automated. The vulnerability affects systems where ProxyChains-NG is used in environments where users may have write access to directories containing the application, making it a significant concern for multi-user systems, development environments, and any scenario where untrusted users might execute applications from shared directories. This weakness can be particularly dangerous when ProxyChains-NG is used in conjunction with other tools or when it is executed with elevated privileges in automated scripts or system services.
Mitigation strategies for CVE-2015-3887 focus primarily on updating to ProxyChains-NG version 4.9 or later, which addresses the untrusted search path issue through proper library loading mechanisms. Organizations should implement strict access controls to prevent unauthorized write access to directories containing the application and its dependencies. System administrators should consider using secure library loading practices such as setting the LD_LIBRARY_PATH environment variable to explicitly define trusted library locations, though this approach must be carefully implemented to avoid breaking legitimate functionality. The implementation of security measures such as SELinux policies or AppArmor profiles can help restrict the ability of local users to manipulate library files in the execution environment. Additionally, regular security audits should verify that applications are not vulnerable to similar library loading issues, as this pattern of vulnerability is commonly found in software that does not properly validate library paths. The remediation approach aligns with ATT&CK technique T1068, which addresses privilege escalation through local exploitation of system vulnerabilities, emphasizing the need for proper library loading security practices as outlined in the MITRE ATT&CK framework.