CVE-2026-10648
MediumCVSS 6.2Exploitation Probability (EPSS)
Low risk2th percentile — higher than 2% of all known CVEs
Summary
In Zephyr RTOS, mcumgr_serial_process_frag() calls net_buf_reset() on the result of smp_packet_alloc() before checking for NULL. When the MCUmgr packet pool (default 4 buffers) is exhausted, smp_packet_alloc() returns NULL, and net_buf_reset() writes through the NULL pointer, causing a system crash. An attacker can flood the serial/UART/shell transport to exhaust the pool and trigger a denial of service.
Risk Assessment
An attacker with access to the serial console or UART can deliberately crash the device, causing a denial of service. The vulnerability affects default Zephyr builds starting from version 4.4.0.
Recommendation
Immediately update Zephyr RTOS to a version containing the fix (moving the NULL check before net_buf_reset). If updating is not possible, restrict physical access to serial/UART/shell interfaces.
Original NVD description (English source)
mcumgr_serial_process_frag() in subsys/mgmt/mcumgr/transport/src/serial_util.c calls net_buf_reset() on the result of smp_packet_alloc() before checking it for NULL. smp_packet_alloc() uses net_buf_alloc(K_NO_WAIT) against the shared MCUmgr packet pool (CONFIG_MCUMGR_TRANSPORT_NETBUF_COUNT, default 4), which returns NULL when the pool is exhausted. In default builds the __ASSERT_NO_MSG in net_buf_reset is a no-op, so net_buf_simple_reset writes through the NULL pointer (buf->len = 0; buf->data = buf->__buf), causing a fault/crash. The fragment data reaches this code from attacker-controlled bytes on the MCUmgr serial/UART/shell-console transports (smp_uart.c, smp_raw_uart.c, smp_shell.c), and a fresh buffer is allocated at the start of essentially every new packet. An attacker on the serial/console link can flood the transport to drive the 4-entry buffer pool to exhaustion and induce the NULL dereference, crashing the device (denial of service). The defect was introduced after the original MCUmgr rework and shipped in Zephyr v4.4.0. The fix moves the NULL check ahead of net_buf_reset.