CVE-2026-74398 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
ipv6: addrconf: bail out of dad_failure when state is no longer POSTDAD
addrconf_dad_failure() transitions ifp->state from DAD to POSTDAD via addrconf_dad_end(), which drops ifp->lock on return. The lock is re-acquired after net_info_ratelimited(). A concurrent ipv6_del_addr() can take the lock in that window, set ifp->state to DEAD and run list_del_rcu(&ifp->if_list).
addrconf_dad_failure() then overwrites DEAD with ERRDAD at errdad: and schedules a new dad_work. The work calls ipv6_del_addr() again, hitting the already-poisoned list entry:
general protection fault: 0000 [#1] SMP NOPTI
CPU: 4 PID: 217 Comm: kworker/4:1 Workqueue: ipv6_addrconf addrconf_dad_work RIP: 0010:ipv6_del_addr+0xe9/0x280 RAX: dead000000000122 Call Trace: addrconf_dad_stop+0x113/0x140 addrconf_dad_work+0x28c/0x430 process_one_work+0x1eb/0x3b0 worker_thread+0x4d/0x400 kthread+0x104/0x140 ret_from_fork+0x35/0x40
Fold the addrconf_dad_end() logic into addrconf_dad_failure() under a single ifp->lock critical section. The STABLE_PRIVACY branch temporarily drops ifp->lock around address regeneration, so at lock_errdad: verify the state is still POSTDAD before transitioning to ERRDAD; bail out otherwise to avoid overwriting a state set by another path while the lock was released.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability exists within the Linux kernel's IPv6 address configuration subsystem where a race condition can lead to kernel memory corruption and system instability. The issue occurs during Duplicate Address Detection (DAD) failure handling when the addrconf_dad_failure() function transitions interface states without proper locking coordination. The flaw stems from the function's design where it calls addrconf_dad_end() to transition from DAD to POSTDAD state, which intentionally releases the ifp->lock before proceeding with additional operations. During this lock release window, concurrent execution paths such as ipv6_del_addr() can acquire the lock and modify interface state to DEAD while the original function continues its execution path.
The race condition manifests when a second execution path attempts to process the same interface after the lock has been released. The addrconf_dad_failure() function reaches a point where it overwrites the DEAD state with ERRDAD at the errdad: label and schedules a new dad_work. However, this work item then calls ipv6_del_addr() again on an already compromised list entry that was modified by the concurrent ipv6_del_addr() execution. This creates a scenario where the kernel attempts to operate on a corrupted data structure, leading to general protection faults and system crashes.
The vulnerability represents a classic race condition pattern that violates proper locking discipline in kernel space operations. According to CWE-362, this constitutes a Concurrent Execution using Shared Resource vulnerability where multiple threads access shared data structures without adequate synchronization. The issue also maps to ATT&CK technique T1059.006 for kernel-level code execution and T1484.001 for privilege escalation through system instability. The root cause lies in the improper handling of interface state transitions during DAD failure processing, where the function assumes exclusive access to the interface data structure throughout its execution.
The fix addresses this by consolidating the addrconf_dad_end() logic into addrconf_dad_failure() under a single critical section protected by ifp->lock. This approach ensures that all operations from DAD failure detection through state transition occur atomically without interruption from concurrent paths. The STABLE_PRIVACY branch temporarily drops the lock during address regeneration, but at the lock_errdad: verification point, the code now explicitly checks that the interface state remains POSTDAD before proceeding with ERRDAD transition. This defensive programming approach prevents overwriting states modified by other execution paths while the lock was released. The solution aligns with kernel security best practices for handling shared data structures and follows established patterns for protecting critical sections in network subsystems.
The operational impact of this vulnerability extends beyond simple system crashes to potential privilege escalation opportunities and denial-of-service conditions. An attacker could potentially exploit this race condition to cause system instability or, in more sophisticated scenarios, manipulate the kernel's memory state through controlled timing of concurrent operations. The vulnerability affects all Linux systems running kernel versions where the IPv6 address configuration subsystem is active, particularly those with dynamic IPv6 address assignment capabilities. System administrators should prioritize patching this vulnerability as it represents a fundamental flaw in kernel memory management during network interface operations and could be leveraged for broader security compromises in environments with multiple concurrent network operations.
The mitigation strategy requires implementing proper locking semantics across all related functions in the IPv6 address configuration subsystem. This involves ensuring that state transitions occur within single critical sections that prevent any concurrent modifications from interfering with ongoing operations. The fix pattern established here should be applied to similar race conditions throughout the kernel networking stack where interface state management occurs. Regular security audits should examine all functions that handle shared network interface data structures for similar patterns of improper locking that could lead to memory corruption vulnerabilities.