CVE-2009-4147 in FreeBSD
Summary
by MITRE
The _rtld function in the Run-Time Link-Editor (rtld) in libexec/rtld-elf/rtld.c in FreeBSD 7.1 and 8.0 does not clear the (1) LD_LIBMAP, (2) LD_LIBRARY_PATH, (3) LD_LIBMAP_DISABLE, (4) LD_DEBUG, and (5) LD_ELF_HINTS_PATH environment variables, which allows local users to gain privileges by executing a setuid or setguid program with a modified variable containing an untrusted search path that points to a Trojan horse library, different vectors than CVE-2009-4146.
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Analysis
by VulDB Data Team • 09/02/2024
The vulnerability described in CVE-2009-4147 resides within the Run-Time Link-Editor component of FreeBSD systems, specifically in the _rtld function located in libexec/rtld-elf/rtld.c. This flaw represents a critical privilege escalation vulnerability that affects FreeBSD versions 7.1 and 8.0, where the runtime linker fails to properly sanitize several critical environment variables during program execution. The vulnerability operates through a privilege escalation vector that leverages the improper handling of environment variables that influence library loading behavior, creating a pathway for local attackers to execute malicious code with elevated privileges.
The technical flaw manifests when setuid or setgid programs execute with modified environment variables that contain untrusted search paths pointing to Trojan horse libraries. The affected environment variables include LD_LIBMAP, LD_LIBRARY_PATH, LD_LIBMAP_DISABLE, LD_DEBUG, and LD_ELF_HINTS_PATH, all of which are crucial for controlling library resolution and loading behavior in Unix-like systems. The root cause stems from the runtime linker's failure to clear these variables before executing setuid programs, allowing attackers to manipulate the library search path and potentially load malicious shared libraries instead of legitimate system libraries. This behavior directly violates the principle of least privilege and creates a dangerous attack surface where trusted system binaries can be subverted.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential system compromise and data exfiltration capabilities. When local users can manipulate the library loading process through environment variable manipulation, they can effectively bypass security controls that rely on proper library resolution. Attackers can craft malicious libraries that contain code to spawn shells, modify system files, or establish persistence mechanisms, all executed with the privileges of the target setuid program. This vulnerability particularly affects programs that have elevated privileges such as those used for system administration, file operations, or network services, making it a significant threat to system integrity and confidentiality. The attack vector is distinct from CVE-2009-4146, indicating a separate but related class of vulnerabilities in the same runtime linking subsystem.
Security mitigations for this vulnerability should focus on implementing proper environment variable sanitization within the runtime linker component, ensuring that all potentially dangerous environment variables are cleared before executing setuid programs. System administrators should apply the relevant FreeBSD security patches that address this specific flaw, while also implementing comprehensive monitoring for unauthorized environment variable modifications. The vulnerability aligns with CWE-250, which addresses "Execute Code with Unusual or Unexpected Privileges," and corresponds to ATT&CK technique T1548.003, "Sudo and Sudo Caching," though the specific mechanism operates through environment variable manipulation rather than direct privilege escalation methods. Organizations should also consider implementing mandatory access controls, privilege separation mechanisms, and regular security auditing to detect and prevent exploitation attempts targeting similar runtime linking vulnerabilities.