CVE-2026-18747
MediumCVSS 6.8Exploitation Probability (EPSS)
Low risk1th percentile - higher than 1% of all known CVEs
Summary
A vulnerability in the SMP-over-console transport in Zephyr RTOS allows an unauthenticated attacker to trigger a buffer length underflow by sending a single 7-byte frame to the management console. This leads to an out-of-bounds read, potentially causing a denial of service on the MCUmgr thread or memory disclosure.
Risk Assessment
An attacker with console access (e.g., USB CDC-ACM port) can remotely crash the system or access memory contents without authentication. The risk includes disruption of device operation and potential exposure of sensitive data.
Recommendation
Update Zephyr RTOS immediately to a version containing the fix that rejects declared packet lengths of two bytes or fewer in mcumgr_serial_extract_len(). If updating is not possible, restrict access to the management console to trusted users only.
Other vulnerabilities in Zephyr RTOS
See all- CVE-2026-82962Medium
A vulnerability in ethernet_fill_header() in the Zephyr RTOS network stack prepends the Ethernet header in place via net_buf_push without verifying that the packet has sufficient headroom. Packets allocated by a different L2 (e.g., 802.15.4/OpenThread, PPP) and handed to Ethernet through routing or tunnelling have too little (usually zero) headroom, causing an out-of-bounds write. In builds without CONFIG_ASSERT and CONFIG_NET_BUF_HARDENING this results in memory corruption.
- CVE-2026-19595Medium
A vulnerability in the Zephyr RTOS syscall verifier: z_vrfy_rtio_cqe_get_mempool_buffer() validated its output parameters buff and buff_len with K_SYSCALL_MEMORY_READ() instead of K_SYSCALL_MEMORY_WRITE(). This allows an unprivileged user-mode thread to invoke the syscall with pointers to read-only memory, causing a supervisor-mode store outside the permitted region or a kernel fault that halts or reboots the device.
- CVE-2026-19940Medium
A vulnerability in the Bluetooth Classic Hands-Free Profile Audio Gateway (HFP AG) implementation in Zephyr RTOS causes corruption of the kernel timeout list. By sending AT+CIND? and quickly reconnecting, a remote attacker can trigger a system-wide fault or hang.
- CVE-2026-19736High
The NXP MCUX TRNG entropy driver in Zephyr (drivers/entropy/entropy_mcux_trng.c) passes the caller's byte count directly to the SDK routine TRNG_GetRandomData(), which on i.MX RT5xx/RT6xx parts always copies whole 32-bit words and rounds entropy draws up to a multiple of 128 bytes. A request length not a multiple of four causes an underflow in the SDK's buffer-full check, leading to an overflow of up to 127 bytes past the caller's buffer.
- CVE-2026-19575High
A vulnerability in Zephyr RTOS affects the user-mode verification handler z_vrfy_device_deinit() in kernel/device.c, which validated its dev argument with K_SYSCALL_OBJ_INIT(dev, K_OBJ_ANY). Because k_object_validate() short-circuits type comparison for K_OBJ_ANY, the check only verified that the pointer was the base address of some kernel object the calling thread was granted, without comparing the object's actual type. This allows a local user-mode thread to pass a thread stack object (e.g., from k_thread_stack_alloc()) and achieve supervisor-mode kernel code execution.
- CVE-2026-19574High
In the ARM64 MMU back-end of Zephyr RTOS, address space identifiers (ASIDs) are assigned by a bare round-robin counter, which after wrapping past 255 possible values can hand the same ASID to a new domain while a still-live domain holds it. Because domain-private mappings are installed as non-global (MT_NG), the ASID is the only tag separating cached translations in the TLB, and the context-switch path does not flush the TLB for a duplicate reached through a third domain. As a result, user-mode threads in one domain can read and write memory belonging to another domain, defeating memory-domain isolation.
- CVE-2026-19569High
A vulnerability in the Zephyr RTOS kernel allows an unprivileged user-mode thread to perform an out-of-bounds write in kernel memory. It stems from missing overflow checks when calculating allocation sizes for dynamic kernel objects, leading to undersized heap allocations. An attacker can exploit this to escalate privileges and execute arbitrary code at the kernel level.
- CVE-2026-19185High
A vulnerability was found in the system-call verifier for i3c_do_ccc() in Zephyr RTOS, which fails to validate per-target data pointers in the i3c_ccc_payload structure. The verifier also operates on the caller's live structure, allowing another thread to modify fields between check and use. This allows an unprivileged thread to write to arbitrary kernel addresses (via read CCC) or disclose kernel memory (via write CCC), leading to privilege escalation.
- CVE-2026-18417Medium
In Zephyr RTOS, a vulnerability exists in the BSD socket layer where an asynchronous error was stored in the user_data field of the network context, which for listening TCP sockets is used to store a pointer to the parent context. In v4.3.0, after an interface-down event, the accept callback was not disarmed, leading to reuse of the poisoned value as a pointer and writes to an invalid address, causing a kernel fatal error (device crash or reset).
- CVE-2026-16513High
A vulnerability in the RTIO syscall verifier in Zephyr RTOS (before v4.3.0) allows an unprivileged user thread to write a pointer to controlled data at an arbitrary kernel address. The missing K_SYSCALL_MEMORY_WRITE check for the handle output parameter enables privilege escalation to kernel mode.
Original NVD description (English source)
The MCUmgr SMP-over-console transport decodes a base64 frame, reads a 16-bit packet length from it, verifies a CRC and then unconditionally strips the trailing CRC with rx_ctxt->nb->len -= 2U; in mcumgr_serial_process_frag() (subsys/mgmt/mcumgr/transport/src/serial_util.c). mcumgr_serial_extract_len() accepted any declared length, including 0 and 1, and a packet declaring length 0 passes the checksum test for free because crc16_itu_t() over zero bytes returns the zero seed. Since net_buf::len is a uint16_t, the subtraction underflows and the buffer is handed to SMP claiming roughly 65 KB of payload while its data area is only CONFIG_MCUMGR_TRANSPORT_NETBUF_SIZE bytes (default 384). The trigger is a single unauthenticated 7-byte line on the management console — the 0x06 0x09 packet marker followed by the base64 group AAA= and a newline — delivered to any transport built on this helper: CONFIG_MCUMGR_TRANSPORT_UART (smp_uart.c) or CONFIG_MCUMGR_TRANSPORT_SHELL (smp_shell.c), both of which select MCUMGR_TRANSPORT_SERIAL_HAS_SMP_OVER_CONSOLE. No prior session state, fragmentation or credentials are required to trigger the underflow, and the malformed frame is mishandled before any command handler or command-level access control runs. The attacker only needs write access to that console, which on many boards is a USB CDC-ACM port rather than a bare UART header. With the inflated length, smp_process_request_packet() in subsys/mgmt/mcumgr/smp/src/smp.c loses its bound: cbor_nb_reader_init() gives the CBOR decoder a ~65 KB window into a 384-byte buffer, and each request header's nh_len is checked only against the inflated length. On its own the 7-byte frame re-parses whatever stale bytes the reused pool buffer still holds, typically a replay of the previously received request followed by a parse error, without leaving the buffer. Because the transport is unauthenticated, though, the attacker also controls the frames sent before the trigger, and can stage buffer contents so that a request succeeds with an nh_len larger than the buffer; net_buf_pull(), guarded only by __ASSERT_NO_MSG, then moves the parse cursor out of bounds and the loop reads further headers and CBOR from adjacent memory. The consequence is an out-of-bounds read that can fault the MCUmgr thread (denial of service); memory disclosure is also possible, since the default-enabled os echo handler (CONFIG_MCUMGR_GRP_OS_ECHO) decodes its string inside that window and copies it into its response. There is no integrity gain beyond what the unauthenticated transport already permits. The fix rejects any declared packet length of two bytes or fewer in mcumgr_serial_extract_len(), so the CRC-strip subtraction can no longer underflow. The identical pattern remains in the test-only loopback transport subsys/mgmt/mcumgr/transport/src/smp_dummy.c (CONFIG_MCUMGR_TRANSPORT_DUMMY), which has no external input path and therefore carries no practical exposure.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS