CVE-2009-1046 in Linux
Summary
by MITRE
The console selection feature in the Linux kernel 2.6.28 before 2.6.28.4, 2.6.25, and possibly earlier versions, when the UTF-8 console is used, allows physically proximate attackers to cause a denial of service (memory corruption) by selecting a small number of 3-byte UTF-8 characters, which triggers an "an off-by-two memory error." NOTE: it is not clear whether this issue crosses privilege boundaries.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability described in CVE-2009-1046 represents a critical memory corruption flaw within the Linux kernel's console handling subsystem that specifically affects UTF-8 console implementations. This issue manifests in kernel versions prior to 2.6.28.4 and 2.6.25, indicating a widespread impact across multiple kernel releases. The vulnerability is particularly concerning because it can be exploited by attackers who are physically proximate to the target system, making it a significant threat in environments where physical access cannot be strictly controlled. The flaw specifically occurs during the console selection feature when processing UTF-8 encoded characters, which are commonly used in internationalized text processing and modern terminal environments.
The technical root cause of this vulnerability is an off-by-two memory error that occurs when the kernel processes a small number of 3-byte UTF-8 characters through the console selection mechanism. This type of memory corruption vulnerability falls under CWE-121, which describes heap-based buffer overflows, and more specifically aligns with CWE-787, which addresses out-of-bounds writes in heap-based buffers. The memory error manifests as a precise two-byte overrun that can corrupt adjacent memory regions, potentially leading to unpredictable system behavior including kernel crashes, memory corruption, or in some cases, potential privilege escalation. The specific nature of the error suggests that the kernel's UTF-8 character processing code fails to properly validate the bounds of memory allocations when handling multi-byte character sequences, particularly those that are three bytes in length.
The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially enable more sophisticated attacks depending on the system configuration and memory layout. When an attacker successfully triggers this memory corruption, the system may experience immediate crashes or more subtle memory corruption that could be exploited to gain elevated privileges or cause more persistent system instability. The fact that this vulnerability can be triggered by physically proximate attackers means that it poses a significant risk in shared computing environments, public terminals, or any system where unauthorized physical access cannot be guaranteed. The attack vector requires minimal complexity to execute, as it only involves selecting specific UTF-8 characters, making it particularly dangerous in environments where console access is not properly secured.
The security implications of this vulnerability align with ATT&CK technique T1068, which covers "Exploitation for Privilege Escalation" and T1499, covering "Endpoint Denial of Service". Organizations should implement immediate mitigations including kernel updates to versions 2.6.28.4 or 2.6.25, as these contain the necessary patches to address the memory corruption issue. Additionally, system administrators should consider implementing physical security measures to prevent unauthorized access to systems where this vulnerability exists, particularly in environments where console access is not properly restricted. The vulnerability also highlights the importance of proper input validation in kernel space code, particularly when handling international character sets that require complex encoding schemes. Regular security assessments should include verification of kernel versions and proper patch management to prevent exploitation of similar memory corruption vulnerabilities in other system components.