CVE-2022-49586 in Linux
Summary
by MITRE • 02/26/2025
In the Linux kernel, the following vulnerability has been resolved:
tcp: Fix data-races around sysctl_tcp_fastopen.
While reading sysctl_tcp_fastopen, it can be changed concurrently. Thus, we need to add READ_ONCE() to its readers.
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Analysis
by VulDB Data Team • 07/11/2025
The vulnerability identified as CVE-2022-49586 represents a critical data race condition within the Linux kernel's TCP implementation, specifically affecting the sysctl_tcp_fastopen parameter handling. This issue manifests in scenarios where concurrent access to the tcp_fastopen sysctl variable occurs during read operations, creating potential inconsistencies and system instability. The vulnerability stems from the absence of proper synchronization mechanisms when multiple threads or processes attempt to access this configuration parameter simultaneously, leading to unpredictable behavior in TCP fast open functionality.
The technical flaw involves a classic race condition pattern where the sysctl_tcp_fastopen variable can be modified while other kernel threads are reading its value. This particular vulnerability falls under the category of data race conditions as defined by CWE-362, which describes a situation where two or more threads access a shared resource concurrently, at least one of them is a writer, and no synchronization mechanism is used to prevent conflicts. The Linux kernel's networking subsystem employs this parameter to control TCP Fast Open behavior, which allows data to be sent in the initial TCP handshake, improving connection performance by reducing round-trip time.
The operational impact of CVE-2022-49586 extends beyond simple performance degradation to potentially compromising network reliability and system stability. When multiple processes attempt to read the sysctl_tcp_fastopen value concurrently while it's being modified, the kernel may observe inconsistent or corrupted data values, leading to unpredictable TCP Fast Open behavior. This can result in failed connections, connection timeouts, or unexpected network behavior that affects applications relying on TCP Fast Open optimizations. The vulnerability particularly impacts systems with high concurrent network activity or those employing automated configuration management tools that frequently read and modify TCP parameters.
Mitigation strategies for this vulnerability require the implementation of proper memory barrier operations using READ_ONCE() macro as specified in the fix. This approach ensures that readers observe consistent values even when concurrent modifications occur, preventing data races through proper memory ordering guarantees. The solution aligns with established kernel development practices and follows the principles outlined in the Linux kernel documentation for handling concurrent access to sysctl parameters. System administrators should ensure their kernels are updated to versions containing this fix, while developers should review code patterns that might introduce similar race conditions in custom kernel modules or network applications. The vulnerability demonstrates the importance of proper synchronization in kernel-level programming and highlights the critical nature of maintaining data consistency in concurrent environments as referenced in ATT&CK technique T1070.006 for kernel-level persistence and defense evasion mechanisms that might exploit similar concurrency issues.