CVE-2006-6535 in Linux
Summary
by MITRE
The dev_queue_xmit function in Linux kernel 2.6 can fail before calling the local_bh_disable function, which could lead to data corruption and "node lockups." NOTE: it is not clear whether this issue is exploitable.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 07/14/2019
The vulnerability described in CVE-2006-6535 resides within the Linux kernel version 2.6, specifically within the dev_queue_xmit function that handles network packet transmission. This flaw represents a critical race condition scenario where the kernel's network subsystem can encounter a failure state before executing the local_bh_disable function, which is responsible for disabling local bottom half handlers during critical network operations. The issue manifests when network packets are queued for transmission but the system fails to properly manage the interrupt handling context, creating a window where kernel data structures may become inconsistent or corrupted. According to industry standards, this vulnerability aligns with CWE-362, which describes a race condition error that can lead to data corruption and system instability. The potential for "node lockups" indicates that the system may become unresponsive or enter a state where normal operations cannot proceed, representing a significant operational risk for networked systems.
The technical implementation of this vulnerability stems from the improper sequencing of kernel operations within the network packet processing pipeline. When dev_queue_xmit encounters certain conditions, it may return early from its execution path without properly initializing the bottom half interrupt handling mechanism that is crucial for maintaining system stability during network operations. This premature exit occurs before local_bh_disable is invoked, which normally ensures that bottom half handlers are suspended during critical sections of network processing. The failure to properly disable these handlers creates an environment where concurrent network processing operations can interfere with each other, potentially leading to memory corruption or inconsistent kernel state. The underlying mechanism involves the kernel's soft interrupt subsystem, where local_bh_disable serves as a critical synchronization primitive that prevents concurrent execution of bottom half handlers that could modify shared data structures.
The operational impact of this vulnerability extends beyond simple data corruption to encompass potential system-wide instability and service disruption. When network subsystems become corrupted or locked up due to this race condition, it can affect all network operations on the affected system, potentially causing complete network outages or system hangs. The severity is compounded by the fact that network operations are fundamental to most modern computing environments, making this vulnerability particularly dangerous in production systems where network connectivity is essential. The uncertainty regarding exploitability, as noted in the original description, suggests that while the vulnerability exists in the kernel code, the precise conditions required to trigger it may be complex or require specific environmental factors. However, the potential for exploitation cannot be dismissed, as race conditions in kernel space often present subtle attack vectors that may be difficult to predict but can be reliably triggered under specific stress conditions.
Mitigation strategies for this vulnerability should focus on both immediate system hardening and long-term architectural improvements. The most direct approach involves applying the appropriate kernel security patches that address the race condition in dev_queue_xmit by ensuring proper ordering of operations and guaranteeing that local_bh_disable is always invoked before potential failure points. System administrators should also implement monitoring solutions that can detect unusual network behavior or system lockup conditions that may indicate the presence of this vulnerability. From an operational perspective, implementing network traffic shaping and load balancing strategies can help reduce the likelihood of triggering the race condition by preventing excessive network load that might exacerbate the timing issues. The vulnerability highlights the importance of kernel-level testing and formal verification techniques, particularly for critical subsystems like network processing, and aligns with ATT&CK framework techniques related to privilege escalation and system exploitation through kernel vulnerabilities. Organizations should also consider implementing intrusion detection systems that can monitor for anomalous network behavior patterns that might indicate exploitation attempts targeting kernel-level race conditions.