CVE-1999-0964 in FreeBSD
Summary
by MITRE
Buffer overflow in FreeBSD setlocale in the libc module allows attackers to execute arbitrary code via a long PATH_LOCALE environment variable.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability described in CVE-1999-0964 represents a critical buffer overflow condition within the FreeBSD operating system's libc module, specifically affecting the setlocale function. This flaw resides in the handling of the PATH_LOCALE environment variable, which is used to specify the location of locale data files. The vulnerability demonstrates a classic buffer overflow scenario where insufficient input validation allows an attacker to write beyond the allocated memory boundaries of the PATH_LOCALE variable. Such a condition creates a potential execution path for malicious code injection through carefully crafted environment variable values that exceed the buffer's capacity.
The technical implementation of this vulnerability involves the setlocale function's processing of locale-related environment variables without proper bounds checking. When the system encounters a PATH_LOCALE environment variable exceeding the predetermined buffer size, the excess data overflows into adjacent memory regions, potentially corrupting critical program state information or overwriting return addresses on the stack. This memory corruption can be exploited to redirect program execution flow to attacker-controlled code, enabling arbitrary code execution with the privileges of the affected process. The vulnerability specifically targets the libc library's locale handling mechanism, which is fundamental to system internationalization and localization features.
The operational impact of this vulnerability extends beyond simple privilege escalation as it can be leveraged in various attack scenarios including local privilege escalation, remote code execution in services running with elevated privileges, and denial of service conditions. Attackers can craft malicious PATH_LOCALE values that not only trigger the buffer overflow but also contain shellcode or payload instructions designed to execute upon program termination or during subsequent locale processing. The vulnerability affects systems running FreeBSD versions that incorporate the affected libc module, potentially impacting a wide range of network services and applications that utilize locale functionality, particularly those that are long-running or accessible to untrusted users.
Mitigation strategies for this vulnerability include immediate patching of affected FreeBSD systems with updated libc libraries containing proper bounds checking and input validation. System administrators should implement environment variable sanitization measures to prevent malicious PATH_LOCALE values from reaching vulnerable applications. The implementation of address space layout randomization and stack canaries can provide additional defense-in-depth measures against exploitation attempts. Furthermore, monitoring for unusual PATH_LOCALE environment variable usage patterns and implementing application whitelisting controls can help detect and prevent exploitation attempts. This vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and maps to ATT&CK technique T1059 for execution through command injection, emphasizing the critical nature of proper input validation in system libraries.