CVE-2023-54195: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-54195 is a NULL pointer dereference vulnerability in the Linux kernel's rxrpc (RxRPC protocol) subsystem. The flaw arises in the interaction between afs_make_call() and rxrpc_kernel_set_max_life(), where a call timer may expire before a connection channel is assigned, triggering a kernel oops. It affects Linux kernel versions in the 6.2 and 6.3 stable series, with fixes backported to 6.2.16, 6.3.3, and 6.4. The vulnerability was published on December 30, 2025, and carries a CVSS base score of 0.0 (no official severity rating assigned at time of publication) (Feedly, EUVD).

The root cause is a race condition / improper sequencing in the rxrpc subsystem (CWE-476: NULL Pointer Dereference). Specifically, afs_make_call() calls rxrpc_kernel_begin_call() to initiate an RxRPC call, which may be queued waiting for a connection. It then immediately calls rxrpc_kernel_set_max_life() to configure timeouts, which starts the call timer prematurely. If the timer fires before a connection channel is granted, the kernel attempts to allocate a transmit buffer (rxrpc_alloc_txbuf) via rxrpc_send_ACK with a NULL pointer, causing a kernel panic. The fix defers timer start until the first packet is transmitted by recording timeouts in struct rxrpc_call at creation time. Direct userspace exploitation via AF_RXRPC is mitigated because sendmsg() returns EBUSY when the call is in the waiting-for-connection state (Feedly, kernel.org patch 6.3).

Successful triggering of this vulnerability causes a kernel NULL pointer dereference, resulting in a kernel oops/panic and system crash — a denial of service (DoS) affecting availability. The crash occurs in the krxrpcio kernel thread context, meaning it can bring down the entire system. There is no evidence of confidentiality or integrity impact, and the vulnerability is not directly exploitable from unprivileged userspace (Feedly).

The Linux kernel maintainers have released patches for the affected stable branches: version 6.2.16 (commit 92128a7170a2), version 6.3.3 (commit 72f4a9f3f447), and the 6.4 mainline release (commit db099c625b13). Users running affected 6.2.x or 6.3.x kernels should upgrade to 6.2.16, 6.3.3, or later. No configuration-based workaround is documented; upgrading to a patched kernel version is the recommended remediation (kernel.org patch 6.2, kernel.org patch 6.3, kernel.org patch mainline).