{"id":"CVE-2026-19595","title":"Zephyr RTIO syscall verifier validates output parameters for read instead of write access","summary":"The user-mode syscall verifier z_vrfy_rtio_cqe_get_mempool_buffer() in subsys/rtio/rtio_syscalls.c validated its two output parameters, buff and buff_len, with K_SYSCALL_MEMORY_READ() rather than K_SYSCALL_MEMORY_WRITE(). Both are pure o…","severity":"medium","cvss":6.1,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H","cvssSource":"cna","cwe":["CWE-787","CWE-822"],"vendor":"zephyrproject","product":"zephyr","affected":["zephyr >= 3.4.0 <= 4.4.2"],"published":"2026-10-19","updated":"2026-10-19","sourceUpdated":"2026-10-19T22:49:40.334Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-19595","references":[{"url":"https://github.com/zephyrproject-rtos/zephyr/commit/bea93400138362691403b7f81de1e9048681547d","label":"Fix commit"},{"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-7337-mc44-5wjm","label":"GHSA-7337-mc44-5wjm"}],"tags":["cve.org"],"ingestedAt":"2026-10-19T23:47:31.358Z","slug":"CVE-2026-19595","body":"## Overview\n\nThe user-mode syscall verifier z_vrfy_rtio_cqe_get_mempool_buffer() in subsys/rtio/rtio_syscalls.c validated its two output parameters, buff and buff_len, with K_SYSCALL_MEMORY_READ() rather than K_SYSCALL_MEMORY_WRITE(). Both are pure out-parameters: z_impl_rtio_cqe_get_mempool_buffer() stores the mempool buffer address and its length through them. The distinction is enforced by every architecture validator — arch_buffer_validate() on RISC-V PMP explicitly accepts the global __rom_region/__rodata_region for reads only, and the ARM MPU validators accept P_RO_U_RO and P_RW_U_RO regions for reads only — so a read-validated pointer is not necessarily writable by the calling thread.\n\nAn unprivileged user-mode thread that has been granted access to an RTIO context (rtio_access_grant()) can invoke the rtio_cqe_get_mempool_buffer() syscall with buff/buff_len pointing at memory it may read but not write, and with a completion-queue entry whose flags field it fully controls (only RTIO_CQE_FLAG_MEMPOOL_BUFFER in flags[7:0] is required; flags[19:8] and flags[31:20] supply the block index and count). The kernel then performs a pointer-sized and a 4-byte store through those addresses while running in supervisor mode. Reaching the store requires CONFIG_USERSPACE together with CONFIG_RTIO_SYS_MEM_BLOCKS, the configuration behind RTIO_DEFINE_WITH_MEMPOOL; without the latter the implementation returns -ENOTSUP and writes nothing.\n\nTwo outcomes follow. If the target lies in a memory-domain partition declared K_MEM_PARTITION_P_RW_U_RO (privileged read-write, user read-only), the kernel-mode store succeeds and deposits partly attacker-chosen values into memory the memory domain had marked read-only for that thread, bypassing the partition's write protection. If the target lies in globally readable but unwritable memory such as .text/.rodata in flash, the store faults in kernel mode; the fault is delivered to z_fatal_error() and the default k_sys_fatal_error_handler() halts or reboots the device, giving an unprivileged thread a reliable full denial of service.\n\nThe read-permission check does bound the damage: the address must still be readable by the calling thread, so kernel-private memory cannot be targeted and no confidential data is disclosed. The fix replaces both checks with K_SYSCALL_MEMORY_WRITE(), so a thread lacking write permission is terminated by K_OOPS before the implementation runs; the cqe argument correctly remains read-validated.\n\n## Affected\n\n- `zephyr >= 3.4.0 <= 4.4.2`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":34,"depthScoreParts":{"impact":33.6,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}