CVE-2026-68342 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
ovpn: avoid putting unrelated P2P peer on socket release
ovpn_peer_release_p2p() is called when an OVPN UDP socket is being destroyed. It checks the currently published P2P peer and releases it only if that peer still uses the socket being destroyed.
A peer replacement can publish a new peer before the old UDP socket is destroyed. When the old socket destruction path runs afterwards, ovpn_peer_release_p2p() observes the new peer through ovpn->peer. Since the new peer uses a different socket, the function takes the socket mismatch branch.
That branch still calls ovpn_peer_put(peer). At this point, however, peer is the currently published replacement peer, not the peer associated with the socket being destroyed. Dropping its reference can free it while ovpn->peer still points to it, leading to later use-after-free accesses from the peer and socket cleanup paths.
KASAN reports this as a slab-use-after-free on the kmalloc-1k ovpn_peer object. In the reproducer, the object is allocated from ovpn_peer_new() via ovpn_nl_peer_new_doit(), and freed through ovpn_peer_release_rcu() from RCU callback processing. Observed access sites include ovpn_peer_remove(), ovpn_socket_release(), ovpn_nl_peer_del_notify(), and unlock_ovpn().
Fix this by returning from the socket mismatch branch without putting the peer.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability described represents a use-after-free condition in the Linux kernel's OpenVPN implementation that arises during the cleanup of UDP sockets associated with peer-to-peer connections. This flaw occurs within the ovpn_peer_release_p2p() function which is invoked when an OVPN UDP socket is being destroyed, creating a race condition scenario where peer replacement operations can interfere with socket cleanup processes. The issue stems from improper reference handling when checking peer associations during socket destruction, leading to potential memory corruption and system instability.
The technical implementation flaw involves the ovpn_peer_release_p2p() function's logic for determining whether to release a P2P peer during socket destruction. When a peer replacement operation occurs before the old socket is fully destroyed, the function observes the new peer through the ovpn->peer pointer rather than the original peer associated with the socket being released. The existing code follows a socket mismatch branch that incorrectly calls ovpn_peer_put(peer) on what appears to be the current peer but is actually the replacement peer from a different socket context. This misidentification leads to premature reference counting and potential memory deallocation of an object that remains referenced elsewhere in the system.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can result in system crashes or privilege escalation opportunities within the kernel's network subsystem. The KASAN (Kernel Address Sanitizer) reporting mechanism identifies this as a slab-use-after-free error on kmalloc-1k allocated ovpn_peer objects, indicating that the memory management subsystem has detected invalid access patterns during the cleanup process. Multiple access sites demonstrate the scope of potential impact including ovpn_peer_remove(), ovpn_socket_release(), ovpn_nl_peer_del_notify(), and unlock_ovpn() functions that may attempt to access freed memory structures.
This vulnerability aligns with CWE-416 (Use After Free) and represents a classic race condition in kernel network driver implementation where concurrent operations interfere with each other's memory management. The ATT&CK framework would categorize this as a privilege escalation technique through kernel memory corruption, potentially enabling attackers to gain elevated privileges or cause denial of service conditions. The fix addresses the root cause by ensuring that when a socket mismatch is detected during peer release, the function returns early without decrementing the reference count of the replacement peer, thereby preventing premature deallocation while maintaining proper cleanup for the actual socket being destroyed.
The resolution strategy focuses on maintaining proper reference counting semantics during concurrent operations where peer replacement can occur before socket destruction completes. By returning from the socket mismatch branch without calling ovpn_peer_put(), the implementation prevents the freeing of a peer object that may still be actively referenced by other system components, particularly in scenarios where RCU (Read-Copy-Update) callback processing is involved. This approach maintains the integrity of the peer reference counting mechanism while ensuring that only peers associated with the specific socket being destroyed undergo proper cleanup and deallocation operations.
The vulnerability demonstrates the complexity of kernel-level synchronization issues in network driver implementations where multiple concurrent operations must maintain consistent state management. The fix requires careful consideration of the existing code flow and ensures that reference counting behavior remains consistent regardless of race conditions between peer replacement and socket destruction paths. This type of vulnerability is particularly dangerous in kernel space because it can lead to arbitrary code execution or system crashes when memory corruption occurs during critical cleanup operations, making proper synchronization and reference management essential for maintaining system stability and security.