CVE-2002-1420 in OpenBSD
Summary
by MITRE
Integer signedness error in select() on OpenBSD 3.1 and earlier allows local users to overwrite arbitrary kernel memory via a negative value for the size parameter, which satisfies the boundary check as a signed integer, but is later used as an unsigned integer during a data copying operation.
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Analysis
by VulDB Data Team • 10/27/2024
The vulnerability described in CVE-2002-1420 represents a critical integer signedness error within the select() system call implementation on OpenBSD versions 3.1 and earlier. This flaw exists at the intersection of kernel space memory management and system call parameter validation, creating a pathway for local privilege escalation through kernel memory corruption. The vulnerability specifically manifests when a negative value is passed as the size parameter to the select() function, where the initial boundary check evaluates this value as a signed integer, allowing it to pass validation criteria that would normally prevent out-of-bounds operations.
The technical execution of this vulnerability relies on the fundamental mismatch between signed and unsigned integer handling within the kernel's memory copying routines. When the select() system call processes a negative size parameter, the initial validation logic treats this value as signed, passing the boundary check because negative values are considered within acceptable ranges for signed integers. However, during the subsequent data copying operation, the same parameter is interpreted as unsigned, causing the kernel to allocate memory based on the absolute value of the negative input. This discrepancy enables attackers to specify memory regions that extend beyond the intended boundaries, effectively allowing arbitrary kernel memory overwrite operations.
The operational impact of this vulnerability extends beyond simple memory corruption, as it provides local attackers with the capability to manipulate kernel data structures and potentially escalate privileges to root access. The flaw operates entirely within the kernel space, making it particularly dangerous because it bypasses normal user-space protections and security mechanisms. According to CWE-195, this vulnerability falls under the category of signed to unsigned conversion errors, which are classified as a common source of memory corruption vulnerabilities in kernel implementations. The attack vector requires local system access, but the potential consequences are severe enough to warrant immediate remediation.
The exploitation of this vulnerability aligns with ATT&CK technique T1068, which describes the use of local privilege escalation techniques through kernel exploits. The attack scenario typically involves a local user executing a crafted program that invokes select() with a negative size parameter, causing the kernel to overwrite memory locations specified by the attacker. This memory corruption can lead to arbitrary code execution within kernel space, potentially allowing the attacker to modify critical system data structures, disable security features, or establish persistent backdoors. The vulnerability demonstrates a classic example of how integer handling errors in system call implementations can create exploitable conditions that compromise entire operating system security models.
Mitigation of this vulnerability requires immediate patching of OpenBSD systems to versions 3.2 or later where the integer signedness error has been corrected. System administrators should also implement additional security measures including kernel hardening techniques, disabling unnecessary system calls, and monitoring for suspicious kernel memory access patterns. The fix typically involves ensuring that all size parameters are properly validated as unsigned integers throughout the entire execution path, preventing the scenario where a negative signed value can be converted to a large positive unsigned value during memory operations. Additionally, organizations should conduct comprehensive security assessments of their kernel-level code to identify similar signedness errors that could potentially exist in other system calls or kernel functions.