CVE-2005-3274 in Linux
Summary
by MITRE
Race condition in ip_vs_conn_flush in Linux 2.6 before 2.6.13 and 2.4 before 2.4.32-pre2, when running on SMP systems, allows local users to cause a denial of service (null dereference) by causing a connection timer to expire while the connection table is being flushed before the appropriate lock is acquired.
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Analysis
by VulDB Data Team • 08/02/2019
The vulnerability described in CVE-2005-3274 represents a critical race condition within the Linux kernel's IP virtual server implementation that specifically affects systems running on symmetric multiprocessing architectures. This flaw exists in the ip_vs_conn_flush function which manages the cleanup of connection tracking entries within the kernel's network layer. The vulnerability manifests when a local user can manipulate the timing of connection timer expirations to occur concurrently with the process of flushing the connection table, creating a scenario where the system attempts to dereference a null pointer during the cleanup operation. The race condition arises from inadequate synchronization mechanisms that fail to properly lock critical sections of code during concurrent access scenarios. This particular vulnerability impacts Linux kernel versions 2.6.x prior to 2.6.13 and 2.4.x prior to 2.4.32-pre2, making it a significant concern for systems running these older kernel versions. The flaw is particularly dangerous because it can be exploited by local users without requiring special privileges, and the exploitation results in a system crash rather than mere denial of service, potentially leading to complete system instability.
The technical implementation of this race condition involves the improper handling of synchronization primitives within the kernel's connection tracking subsystem. When the ip_vs_conn_flush function executes, it attempts to clean up expired connection entries while other kernel threads may be modifying the connection table simultaneously. The absence of proper locking mechanisms during the critical section where connection entries are accessed and modified creates an opportunity for a null pointer dereference when the connection timer expires and attempts to access a connection entry that has already been freed or is in the process of being freed. This type of race condition is classified under CWE-362, which specifically addresses the issue of concurrent execution of multiple threads or processes without proper synchronization. The vulnerability exploits the fundamental flaw in the kernel's design where the connection table management does not adequately protect against simultaneous read and write operations that can occur during the flush operation.
The operational impact of this vulnerability extends beyond simple denial of service, as it can result in complete system crashes that require manual intervention to restore normal operation. Local users who exploit this vulnerability can cause the kernel to panic and restart, leading to service disruption for all network services that depend on the IP virtual server functionality. The timing aspect of the exploitation makes this particularly challenging to defend against since it relies on specific conditions that may be difficult to predict or prevent in production environments. The vulnerability affects systems running on SMP architectures where multiple processors can execute kernel threads simultaneously, making it relevant for server environments and high-performance computing systems. Additionally, the impact is significant because it can be exploited by any local user with access to the system, meaning that even unprivileged accounts can potentially cause system-wide disruptions. This vulnerability aligns with ATT&CK technique T1499.004, which covers the exploitation of kernel vulnerabilities for denial of service purposes.
Mitigation strategies for this vulnerability require immediate kernel updates to versions that contain the appropriate fixes for the race condition in ip_vs_conn_flush. System administrators should prioritize upgrading to kernel versions 2.6.13 or 2.4.32-pre2 and later, which include proper synchronization mechanisms that prevent the race condition from occurring. The fix typically involves implementing appropriate locking mechanisms around the critical sections of the connection table management code, ensuring that connection entries are not accessed or modified concurrently during the flush operation. Organizations should also consider implementing monitoring solutions that can detect anomalous behavior patterns that may indicate exploitation attempts, particularly in environments where local access is possible. While the vulnerability itself is relatively straightforward to exploit, the mitigation approach should focus on both immediate patching and long-term monitoring to prevent potential exploitation. The fix addresses the underlying synchronization issue and ensures that connection table cleanup operations are properly protected against concurrent access, thereby preventing the null pointer dereference that leads to system crashes.