CVE-2026-64545 in Linux
Summary
by MITRE • 07/28/2026
In the Linux kernel, the following vulnerability has been resolved:
net, bpf: check master for NULL in xdp_master_redirect()
xdp_master_redirect() dereferences the result of netdev_master_upper_dev_get_rcu() without a NULL check, but that helper returns NULL when the receiving device has no upper-master adjacency.
The reach guard only checks netif_is_bond_slave(). On bond slave release bond_upper_dev_unlink() drops the upper-master adjacency before clearing IFF_SLAVE, so an XDP_TX reaching xdp_master_redirect() in that window still passes netif_is_bond_slave() while master is already NULL, and faults on master->flags at offset 0xb0:
BUG: kernel NULL pointer dereference, address: 00000000000000b0 RIP: 0010:xdp_master_redirect (net/core/filter.c:4432) Call Trace: xdp_master_redirect (net/core/filter.c:4432) bpf_prog_run_generic_xdp (include/net/xdp.h:700) do_xdp_generic (net/core/dev.c:5608) __netif_receive_skb_one_core (net/core/dev.c:6204) process_backlog (net/core/dev.c:6319) __napi_poll (net/core/dev.c:7729) net_rx_action (net/core/dev.c:7792) handle_softirqs (kernel/softirq.c:622) __dev_queue_xmit (include/linux/bottom_half.h:33) packet_sendmsg (net/packet/af_packet.c:3082) __sys_sendto (net/socket.c:2252) Kernel panic - not syncing: Fatal exception in interrupt
The missing check dates back to the original code; commit 1921f91298d1 ("net, bpf: fix null-ptr-deref in xdp_master_redirect() for down master") later added the master->flags read where the fault now lands but kept the unconditional deref. Check master for NULL before use; a NULL master is treated the same as one that is not up.
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Analysis
by VulDB Data Team • 07/28/2026
The vulnerability exists within the Linux kernel's networking stack, specifically in the eXpress Data Path (XDP) implementation where the xdp_master_redirect() function performs an unsafe dereference of a potentially null pointer. This flaw occurs when processing XDP_TX operations on bonded network interfaces, creating a race condition that can lead to kernel panics and system instability. The issue stems from the function's failure to properly validate the return value from netdev_master_upper_dev_get_rcu(), which is designed to retrieve the upper master device of a network interface but returns NULL when no such adjacency exists.
The technical implementation flaw manifests through a race condition involving bond slave devices during their lifecycle transitions. When a bond slave interface is being released, the function bond_upper_dev_unlink() executes before clearing the IFF_SLAVE flag, creating a temporal window where netif_is_bond_slave() still returns true while the master pointer has already been set to NULL. This condition allows xdp_master_redirect() to proceed with dereferencing master without proper validation, leading to a null pointer dereference at offset 0xb0 in the master structure's flags field. The vulnerability is particularly dangerous because it operates within kernel space interrupt context, making it capable of causing immediate system crashes and potential denial of service conditions.
The operational impact of this vulnerability extends beyond simple system instability, as it can be exploited to cause kernel panics that require manual system restarts and potentially compromise network availability in production environments. The fault occurs during packet processing flows involving XDP_TX operations, where network packets are redirected through the XDP framework before reaching their final destination, making this a critical vulnerability for systems relying on high-performance networking capabilities. This issue affects systems using bonded network interfaces with XDP enabled, particularly those implementing high-throughput network processing scenarios such as load balancers, network virtualization platforms, and high-frequency trading systems.
The mitigation strategy involves implementing a simple but crucial null pointer check before dereferencing the master pointer in xdp_master_redirect(). The fix requires checking whether master is NULL prior to accessing its flags field, treating a NULL master the same as a down master device. This approach aligns with standard kernel security practices and follows the principle of defensive programming where all pointers are validated before use. The solution addresses the root cause by ensuring proper error handling in the face of race conditions rather than attempting to eliminate the race condition itself, which would be more complex and potentially introduce performance regressions.
This vulnerability type maps directly to CWE-476, Null Pointer Dereference, and falls under the ATT&CK technique T1059.003, Command and Scripting Interpreter: Windows Command Shell, when considering indirect exploitation paths through network packet manipulation. The fix demonstrates proper kernel security engineering practices by implementing early validation checks in kernel code paths that handle critical networking operations, ensuring robustness against race conditions and improper state transitions in complex network interface management scenarios. The solution maintains backward compatibility while adding necessary safety guards to prevent the kernel from crashing during legitimate network operations involving bonded interfaces with XDP acceleration enabled.