CVE-2026-68323 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
tipc: serialize udp bearer replicast list updates
tipc_udp_rcast_add() and cleanup_bearer() both update ub->rcast.list with list_add_rcu() / list_del_rcu(), but nothing serializes them. The add runs from the encap receive softirq (via tipc_udp_rcast_disc()) without rtnl_lock(), so it can race the cleanup delete and corrupt the list:
list_del corruption. prev->next should be ffff8880298d7ab8, but was ffff88802449ad38. (prev=ffff888027e3ec98) kernel BUG at lib/list_debug.c:62! RIP: __list_del_entry_valid_or_report+0x17a/0x200 Workqueue: events cleanup_bearer Call Trace: cleanup_bearer (net/tipc/udp_media.c:811) process_one_work (kernel/workqueue.c:3302) worker_thread (kernel/workqueue.c:3466)
The bearer can be enabled from an unprivileged user namespace, as the TIPCv2 generic-netlink ops carry no GENL_ADMIN_PERM.
Add a spinlock to struct udp_bearer and take it around the list_add_rcu() in tipc_udp_rcast_add() and the list_del_rcu() loop in cleanup_bearer() so the two writers can no longer corrupt the list.
Reject a duplicate peer under the same lock before allocating, and remove tipc_udp_is_known_peer(). The old lockless pre-check in tipc_udp_rcast_disc() was racy: two softirqs discovering the same peer could both find it absent and add it twice.
cleanup_bearer() runs from a workqueue after tipc_udp_disable() clears the bearer's up bit, so an encap softirq can still reach tipc_udp_rcast_add() and add a peer after cleanup_bearer() has already emptied the list, leaking that entry when the bearer is freed. Mark the bearer disabled under rcast_lock once the list is emptied and refuse further additions.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability described affects the Linux kernel's TIPC (Transparent Inter-Process Communication) implementation, specifically within the UDP media bearer component. This issue stems from a race condition in the handling of replicast list updates where concurrent operations can lead to memory corruption and potential system instability. The flaw occurs when multiple threads attempt to modify the same data structure without proper synchronization mechanisms.
The technical root cause involves the tipc_udp_rcast_add() function and cleanup_bearer() function both manipulating the ub->rcast.list data structure using RCU (Read-Copy-Update) list operations without adequate serialization. The add operation occurs within an encapsulation receive softirq context, which executes outside of the rtnl_lock(), creating a window where concurrent access can corrupt the linked list structure. This race condition manifests as list corruption errors where the prev->next pointers become invalid, leading to kernel panics and system crashes.
The vulnerability's operational impact extends beyond simple memory corruption, as it enables potential privilege escalation scenarios. The TIPCv2 generic-netlink operations lack proper permission checks, allowing unprivileged user namespaces to enable the bearer functionality. This creates an attack surface where malicious users can trigger the race condition through crafted network packets, potentially leading to system crashes or more severe consequences depending on the execution context.
The mitigation strategy addresses this by implementing proper synchronization using spinlocks around the critical sections that modify the replicast list. Specifically, a spinlock is added to the udp_bearer structure and utilized during both list_add_rcu() operations in tipc_udp_rcast_add() and the list_del_rcu() processing loop in cleanup_bearer(). This serialization prevents concurrent modifications while maintaining the performance characteristics required for real-time network communication.
Additional improvements include rejecting duplicate peer entries under the protection of the same lock mechanism, eliminating the previous lockless pre-check that was prone to race conditions. The removal of tipc_udp_is_known_peer() function eliminates a source of potential inconsistencies in peer tracking and ensures all peer additions are properly validated under the protective lock context. Furthermore, the fix implements a mechanism to mark the bearer as disabled once the replicast list is emptied, preventing any further additions even after cleanup_bearer() has been initiated but before the bearer is fully freed.
This vulnerability aligns with CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) and demonstrates how improper locking in kernel space can lead to critical system instability. The ATT&CK framework categorizes this under privilege escalation through kernel vulnerabilities, as the race condition could potentially be exploited to gain elevated privileges within the kernel context. The fix ensures proper atomicity of list operations while maintaining the required network functionality for TIPC's UDP media bearer implementation.
The solution follows established kernel development practices for handling concurrent data structure modifications and demonstrates the importance of proper synchronization mechanisms in high-performance kernel subsystems. The use of spinlocks rather than more heavyweight mutexes maintains system responsiveness while ensuring data integrity during critical operations. This approach aligns with Linux kernel best practices for protecting shared data structures in interrupt contexts where traditional locking mechanisms may not be suitable.