CVE-2026-85035 (GCVE-0-2026-85035)
Vulnerability from cvelistv5 – Published: 2026-11-03 13:36 – Updated: 2026-11-03 18:13
VLAI
EPSS
VEX
Title
Use-after-free via dynamically allocated message queue retained by the CAN RX filter
Summary
The can_add_rx_filter_msgq() system call installs a CAN RX filter whose callback (can_msgq_put() in drivers/can/can_common.c) is handed the caller's struct k_msgq * as user_data. The controller driver stores that raw pointer in its filter table and dereferences it from the RX path every time a matching frame arrives. The system call verifier z_vrfy_can_add_rx_filter_msgq() in drivers/can/can_handlers.c validated the queue only with K_SYSCALL_OBJ(), which is a point-in-time check of type, initialization and caller permission and says nothing about the object's lifetime.
On a build with CONFIG_USERSPACE=y and CONFIG_DYNAMIC_OBJECTS=y, an unprivileged user-mode thread that has been granted access to a CAN device can obtain a message queue whose lifetime it fully controls: k_object_alloc(K_OBJ_MSGQ) followed by k_msgq_alloc_init(). The lifetime of such an object is driven solely by its permission bitmask, and a pointer retained by the kernel is not represented there. After registering the filter, the thread calls k_object_release() — or simply terminates — and unref_check() frees the struct k_msgq storage while the CAN driver still holds the pointer.
The next matching CAN frame causes k_msgq_put() to run in supervisor context against freed memory that the attacker can have groomed with another kernel allocation: the frame payload is memcpy()d through the reused block's write_ptr, and the queue's wait_q (and poll_events under CONFIG_POLL) list nodes are manipulated. This yields kernel-heap corruption reachable from a user-mode thread, defeating the isolation CONFIG_USERSPACE is intended to provide; the same dangling pointer also arises benignly when an application thread exits without calling can_remove_rx_filter().
The fix validates the queue with K_SYSCALL_OBJ_STATIC(), which additionally rejects objects carrying K_OBJ_FLAG_ALLOC, so only statically defined queues (CAN_MSGQ_DEFINE()) may be registered from user mode. Supervisor-mode callers bypass the verifier and must themselves keep the queue valid until the filter is removed.
Severity
8.8 (High)
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-11-03 18:13 UTC
CWE
- CWE-416 - use-after-free
Assigner
References
2 references
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| zephyrproject | zephyr |
Affected:
1.14.0 , < 4.3.2
(semver)
Affected: 4.4.0 , < 4.5.0 (semver) |
guessed |
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