{"id":"CVE-2026-19595","aliases":["EUVD-2026-104665","GHSA-7337-mc44-5wjm"],"status":"published","title":"Zephyr RTIO syscall verifier validates output parameters for read instead of write access","description":"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 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.","severity":{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00145,"percentile":0.03804,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-787","CWE-822"],"published":"2026-10-19T22:49:40Z","modified":"2026-11-04T05:18:49Z","products":[{"vendor":"zephyrproject","product":"zephyr"},{"vendor":"zephyrproject-rtos","product":"zephyr"}],"references":[{"url":"https://github.com/zephyrproject-rtos/zephyr/commit/bea93400138362691403b7f81de1e9048681547d","tags":["patch","fix"]},{"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-7337-mc44-5wjm","tags":["advisory"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/19xxx/CVE-2026-19595.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-19595","tags":["advisory"]},{"url":"https://github.com/zephyrproject-rtos/zephyr","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-19595","title":"Zephyr RTIO syscall verifier validates output parameters for read instead of write access","description":"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 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.","status":"published","published":"2026-10-19T22:49:40.334Z","modified":"2026-11-04T05:01:16.762Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H","level":"medium","assessor":"cna"}],"cwes":["CWE-787","CWE-822"],"updated_at":"2026-11-04T06:53:01.479776Z"}],"euvd":[{"id":"EUVD-2026-104665","description":"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 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.","status":"published","published":"2026-10-19T22:49:40Z","modified":"2026-11-04T05:01:16Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H","level":"medium"}],"updated_at":"2026-11-04T07:00:56.104537Z"}],"nvd":[{"id":"CVE-2026-19595","description":"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 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.","status":"published","published":"2026-10-19T23:17:36.717Z","modified":"2026-11-04T05:18:49.41Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H","level":"medium","assessor":"secondary"}],"cwes":["CWE-787","CWE-822"],"updated_at":"2026-11-04T06:53:25.669219Z"}],"osv":[{"id":"CVE-2026-19595","title":"Zephyr RTIO syscall verifier validates output parameters for read instead of write access","description":"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 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.","status":"published","published":"2026-10-19T22:49:40.334Z","modified":"2026-11-05T03:31:26.741147041Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H","level":"medium"}],"cwes":["CWE-787","CWE-822"],"updated_at":"2026-11-05T07:12:28.867005Z"}]}}