CVE-2006-4516 in FreeBSD
Summary
by MITRE
Integer signedness error in FreeBSD 6.0-RELEASE allows local users to cause a denial of service (memory corruption and kernel panic) via a PT_LWPINFO ptrace command with a large negative data value that satisfies a signed maximum value check but is used in an unsigned copyout function call.
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Analysis
by VulDB Data Team • 04/24/2026
The vulnerability described in CVE-2006-4516 represents a critical integer signedness error within the FreeBSD 6.0-RELEASE operating system kernel. This flaw exists in the ptrace system call implementation, specifically affecting the PT_LWPINFO command which is used for debugging and process tracing operations. The issue stems from a fundamental mismatch in how integer values are handled during kernel operations, creating a path for malicious local users to exploit the system's memory management functions. The vulnerability demonstrates a classic case of improper input validation where signed integer values are incorrectly processed through unsigned functions, leading to unpredictable behavior in kernel memory operations.
The technical root cause of this vulnerability lies in the kernel's handling of ptrace commands where a large negative integer value is passed to the PT_LWPINFO function. During the validation process, this value satisfies a signed maximum value check that is designed to prevent buffer overflows or other malicious inputs. However, the same value is subsequently passed to an unsigned copyout function call that expects unsigned integer parameters. This mismatch causes the kernel to interpret the negative value as a large positive unsigned integer, leading to memory corruption when attempting to copy data out of kernel space. The signedness error creates a condition where valid input parameters trigger invalid memory operations, ultimately resulting in kernel panic and system instability.
From an operational perspective, this vulnerability presents a significant risk to FreeBSD systems running version 6.0-RELEASE as it allows local users to perform a denial of service attack that can bring down the entire system. The impact extends beyond simple service disruption since kernel panics can lead to data loss, system crashes, and potential compromise of the system's integrity. Attackers exploiting this vulnerability can cause the system to become unresponsive, requiring manual intervention for recovery, which can be particularly problematic in production environments where uptime is critical. The nature of the flaw means that any user with access to the system can potentially trigger the vulnerability, making it a serious concern for system administrators who must consider the security implications of local user access.
The vulnerability aligns with CWE-195, which addresses signed to unsigned conversion errors, and demonstrates how such issues can lead to memory corruption and system instability. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and system resource hijacking, as local users can leverage the denial of service capability to disrupt system operations. The exploitation pattern follows the typical attack chain where an attacker identifies a kernel-level vulnerability, crafts malicious input parameters that satisfy validation checks, and then triggers memory corruption through improper data handling. Organizations should consider implementing kernel hardening measures and ensure timely patching of affected systems. Additionally, monitoring for unusual ptrace activity and implementing proper access controls can help detect and prevent exploitation attempts. The vulnerability underscores the importance of rigorous input validation and proper handling of integer types in kernel code, particularly when transitioning between signed and unsigned contexts.