CVE-2003-1234 in FreeBSD
Summary
by MITRE
Integer overflow in the f_count counter in FreeBSD before 4.2 through 5.0 allows local users to cause a denial of service (crash) and possibly execute arbitrary code via multiple calls to (1) fpathconf and (2) lseek, which do not properly decrement f_count through a call to fdrop.
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Analysis
by VulDB Data Team • 09/02/2019
The vulnerability described in CVE-2003-1234 represents a critical integer overflow condition within the FreeBSD operating system kernel that affects versions prior to 4.2 through 5.0. This flaw exists in the file descriptor management subsystem where the f_count counter variable, which tracks the number of references to a file descriptor, fails to properly decrement when file operations are performed. The issue manifests when local attackers execute multiple calls to specific system functions that should maintain proper reference counting but do not adequately handle the decrementing process through the fdrop function call. This fundamental design flaw in the kernel's file descriptor management creates a scenario where the counter can wrap around to a very large positive value when it should be decrementing, leading to unpredictable system behavior.
The technical exploitation of this vulnerability occurs through carefully crafted sequences of system calls that manipulate the file descriptor reference counter. When attackers repeatedly invoke fpathconf and lseek system calls in specific patterns, they can cause the f_count variable to overflow and wrap around, potentially leading to memory corruption and system instability. The integer overflow condition can result in the kernel attempting to access invalid memory locations or manipulate file descriptor structures in unexpected ways. This vulnerability falls under CWE-190, which specifically addresses integer overflow conditions, and aligns with the broader category of kernel-level memory corruption vulnerabilities that can lead to privilege escalation or system compromise. The flaw demonstrates a classic buffer overflow pattern where insufficient bounds checking leads to arithmetic overflow conditions that can be exploited for denial of service or code execution.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to potentially enable arbitrary code execution on vulnerable systems. When the f_count counter overflows, the kernel's reference counting mechanism becomes corrupted, which can lead to double-free conditions, memory corruption, or invalid pointer dereferences. Local attackers who can access the system with normal user privileges can leverage this vulnerability to crash the operating system or potentially execute malicious code with kernel-level privileges. The attack vector is particularly concerning because it requires only local access and does not need network connectivity or special privileges beyond standard user accounts. This makes the vulnerability especially dangerous in multi-user environments where local attackers might have access to legitimate user accounts and can exploit this condition to gain elevated privileges or cause persistent system outages. The vulnerability also aligns with ATT&CK technique T1068, which covers the use of privilege escalation techniques through kernel-level exploits, and T1499, which addresses the use of system resource exploitation for denial of service attacks.
Mitigation strategies for this vulnerability require immediate system updates to FreeBSD versions that contain the necessary patches for proper reference counting in the file descriptor subsystem. System administrators should prioritize upgrading to FreeBSD 4.2 or later releases that address this specific integer overflow condition. Additionally, implementing proper input validation and bounds checking in kernel code can prevent similar issues from occurring in the future. The vulnerability highlights the importance of thorough testing of arithmetic operations in kernel space and the need for comprehensive security reviews of core operating system components. Organizations should also consider implementing monitoring solutions to detect unusual patterns of file system calls that might indicate exploitation attempts, as well as maintaining up-to-date system patches and security configurations to prevent exploitation of similar kernel-level vulnerabilities. The fix implemented in later FreeBSD versions ensures proper decrementing of the f_count counter through correct handling of the fdrop function calls, preventing the integer overflow condition from occurring during legitimate file system operations.