CVE-2026-74262 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
kcm: use WRITE_ONCE() when changing lower socket callbacks
kcm_attach() replaces a live lower TCP socket's sk_data_ready and sk_write_space callbacks with KCM handlers, and kcm_unattach() restores them later. Those callback-pointer updates are still plain stores even though the same fields can be read and invoked concurrently on other CPUs.
If another CPU observes an older callback snapshot after the live field has already been restored, callback execution can run with a mismatched target and sk_user_data state, leading to stale or misdirected wakeups.
Use WRITE_ONCE() for the callback replacement and restore operations so these shared callback fields follow the same visibility contract already established by the earlier 4022 fixes.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability in question resides within the Linux kernel's key management module KCM implementation, specifically addressing a race condition during socket callback management. This issue affects the kcm_attach() and kcm_unattach() functions which handle the manipulation of TCP socket callbacks for KCM operations. The flaw stems from improper synchronization mechanisms when updating shared callback pointers that are simultaneously accessed by multiple CPU cores. When kcm_attach() replaces the lower TCP socket's sk_data_ready and sk_write_space callbacks with KCM-specific handlers, and kcm_unattach() restores them later, these operations use plain memory stores instead of proper atomic operations.
The technical core of this vulnerability involves a classic race condition scenario where concurrent execution across multiple CPU cores creates inconsistent states in callback pointer management. The issue is particularly concerning because the same fields that are updated during attach/unattach operations can be read and invoked concurrently on other CPUs, creating a window where different CPU cores observe different states of the callback pointers. This inconsistency occurs when one CPU observes an older callback snapshot after the live field has already been restored, resulting in callback execution that operates with mismatched targets and sk_user_data state information.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable misdirected wakeups and stale data handling within the networking stack. When callback execution runs with inconsistent target references and state information, it can lead to unpredictable behavior in network packet processing and socket state management. The mismatched callback execution can cause system instability, data loss, or potentially allow for privilege escalation scenarios where malicious actors could exploit the inconsistent state transitions. This vulnerability directly relates to CWE-362 which addresses race conditions in concurrent programming, and aligns with ATT&CK technique T1059.007 for execution through kernel modules.
The fix implemented involves using WRITE_ONCE() macro for the callback replacement and restore operations, ensuring that these shared callback fields maintain consistent visibility semantics across all CPU cores. This approach mirrors the established patterns from earlier kernel fixes referenced in commit 4022, which had already addressed similar synchronization issues in the same codebase. The WRITE_ONCE() mechanism provides the necessary memory ordering guarantees to prevent reordering of memory operations while maintaining performance characteristics. By adopting this standard approach, the fix ensures that callback pointer updates follow the same visibility contract already established for other shared kernel structures, eliminating the race condition that could lead to stale or misdirected wakeups. This solution aligns with Linux kernel best practices for concurrent programming and maintains the integrity of socket callback management across multi-core systems while preserving system stability and security properties.