CVE-2021-47248 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
udp: fix race between close() and udp_abort()
Kaustubh reported and diagnosed a panic in udp_lib_lookup(). The root cause is udp_abort() racing with close(). Both racing functions acquire the socket lock, but udp{v6}_destroy_sock()
release it before performing destructive actions.
We can't easily extend the socket lock scope to avoid the race, instead use the SOCK_DEAD flag to prevent udp_abort from doing any action when the critical race happens.
Diagnosed-and-tested-by: Kaustubh Pandey <[email protected]>
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Analysis
by VulDB Data Team • 08/07/2026
The vulnerability identified as CVE-2021-47248 represents a critical race condition within the Linux kernel's UDP implementation that can lead to system panics and potential denial of service conditions. This issue specifically affects the interaction between the udp_abort() and close() functions during socket cleanup operations, creating a scenario where concurrent execution of these functions can result in unpredictable system behavior and kernel crashes. The vulnerability manifests when the kernel attempts to handle UDP socket termination under specific timing conditions, making it particularly dangerous in network-intensive environments where socket operations occur frequently.
The technical flaw stems from the improper synchronization between two critical socket management functions within the UDP subsystem. Both udp_abort() and close() functions acquire the socket lock to ensure exclusive access to socket resources, yet the socket lock is released before destructive operations begin in udp{v6}_destroy_sock(). This creates a window where udp_abort() can attempt to operate on a socket that is simultaneously being closed by the close() function, leading to memory corruption and system instability. The race condition occurs because the socket lock scope is insufficient to protect against this specific interaction pattern, particularly when the socket is in a transitional state between being marked for closure and actually being destroyed.
The operational impact of this vulnerability extends beyond simple system crashes, potentially allowing attackers to trigger denial of service conditions in network services that rely heavily on UDP socket operations. When a system experiences this race condition, it can result in immediate kernel panics that require system reboot to recover from, disrupting network services and potentially affecting other system components that depend on stable network operations. The vulnerability affects all Linux kernel versions that implement the problematic UDP socket management logic, making it a widespread concern for network infrastructure and server environments where UDP traffic processing is common.
The fix implemented for CVE-2021-47248 addresses the race condition by introducing the SOCK_DEAD flag mechanism to prevent udp_abort() from performing destructive actions when the race condition occurs. This approach avoids the complexity of extending socket lock scopes, which would have required significant architectural changes to the socket subsystem. The solution leverages the existing socket state management infrastructure to provide a clean synchronization mechanism that prevents the abort function from operating on sockets that are in the process of being closed. This mitigation strategy aligns with established security practices for race condition resolution and follows the principle of least privilege in kernel space operations.
From a cybersecurity perspective, this vulnerability demonstrates the importance of proper synchronization in kernel-level code and the potential for seemingly minor race conditions to cause significant system instability. The issue relates to CWE-362, which specifically addresses race conditions in concurrent programming, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. The vulnerability highlights the need for comprehensive testing of concurrent code paths in kernel space, particularly in network protocol implementations where timing-sensitive operations are common. Organizations should prioritize patching this vulnerability as it represents a potential attack vector for network-based denial of service attacks that could disrupt critical infrastructure services relying on UDP communications.