CVE-2026-90170 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: validate ipc response length before dereferencing its fields
ipc_validate_msg() computes the expected message size by reading length fields out of the response buffer supplied by the userspace ksmbd daemon (payload_sz, session_key_len, ngroups, ...). Those fields are read before the buffer is verified to be large enough to contain the struct they belong to, so a short response makes the read land past the end of the allocation.
handle_response() sizes entry->response purely from the netlink attribute length (nla_len()) and only guards the leading handle read, so the daemon can install a response as small as the kmalloc-8 object seen below. When ipc_msg_send_request() then calls ipc_validate_msg() for a KSMBD_EVENT_RPC_REQUEST, the cast to struct ksmbd_rpc_command reads resp->payload_sz at offset 8 of an 8-byte allocation:
[ 3697.841381] ==================================================================
[ 3697.844099] BUG: KASAN: slab-out-of-bounds in ipc_msg_send_request+0x763/0x800
[ 3697.846604] Read of size 4 at addr ffff888105f95910 by task kworker/4:3/20682
[ 3697.849061]
[ 3697.849801] CPU: 4 UID: 0 PID: 20682 Comm: kworker/4:3 Not tainted 7.2.0-rc3-next-20260717-virtme #117 PREEMPT(lazy)
[ 3697.850077] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[ 3697.850303] Workqueue: ksmbd-io handle_ksmbd_work
[ 3697.850592] Call Trace:
[ 3697.850794] <TASK>
[ 3697.850952] __dump_stack+0x21/0x60
[ 3697.851239] dump_stack_lvl+0xc2/0x100
[ 3697.851528] print_address_description+0x77/0x200
[ 3697.851816] ? ipc_msg_send_request+0x763/0x800
[ 3697.852024] print_report+0x58/0x70
[ 3697.852316] kasan_report+0x117/0x150
[ 3697.852585] ? down_write+0x146/0x1f0
[ 3697.852809] ? ipc_msg_send_request+0x763/0x800
[ 3697.853082] ipc_msg_send_request+0x763/0x800
[ 3697.853385] ? __pfx_ipc_msg_send_request+0x10/0x10
[ 3697.853604] ? kasan_unpoison+0x48/0x70
[ 3697.853936] ? __pfx___up_read+0x10/0x10
[ 3697.854221] ksmbd_rpc_ioctl+0x380/0x520
[ 3697.854542] ? __pfx_ksmbd_rpc_ioctl+0x10/0x10
[ 3697.854757] ? kasan_unpoison+0x48/0x70
[ 3697.854962] ? copy_from_kernel_nofault+0x32c/0x4e0
[ 3697.855166] ? kasan_unpoison+0x48/0x70
[ 3697.855416] fsctl_pipe_transceive+0x139/0x7a0
[ 3697.855705] ? __pfx_copy_from_kernel_nofault+0x10/0x10
[ 3697.855937] ? __pfx_fsctl_pipe_transceive+0x10/0x10
[ 3697.856388] ? __sanitizer_cov_trace_switch+0x7b/0x140
[ 3697.856620] smb2_ioctl+0x1141/0x3420
[ 3697.856994] ? __pfx_smb2_ioctl+0x10/0x10
[ 3697.857182] ? get_smb2_cmd_val+0xe3/0x1c0
[ 3697.857655] handle_ksmbd_work+0x9ad/0x15e0
[ 3697.858034] ? __pfx_handle_ksmbd_work+0x10/0x10
[ 3697.858251] ? lock_release+0xf7/0x360
[ 3697.858466] ? process_scheduled_works+0x954/0x1600
[ 3697.858698] ? process_scheduled_works+0x954/0x1600
[ 3697.858905] process_scheduled_works+0xc22/0x1600
[ 3697.859368] ? __pfx_process_scheduled_works+0x10/0x10
[ 3697.859637] ? __pfx_assign_work+0x10/0x10
[ 3697.859896] ? lock_is_held_type+0x7b/0x110
[ 3697.860146] worker_thread+0x975/0xee0
[ 3697.860524] ? __pfx_do_raw_spin_lock+0x10/0x10
[ 3697.860830] ? __kthread_parkme+0x21e/0x260
[ 3697.861105] kthread+0x3a6/0x490
[ 3697.861423] ? __pfx_worker_thread+0x10/0x10
[ 3697.861643] ? __pfx_kthread+0x10/0x10
[ 3697.861878] ret_from_fork+0x55a/0xa20
[ 3697.862194] ? __pfx_ret_from_fork+0x10/0x10
[ 3697.862480] ? __pfx_kthread+0x10/0x10
[ 3697.862714] ret_from_fork_asm+0x1a/0x30
[ 3697.862965] </TASK>
[ 3697.863039]
[ 3697.938882] Allocated by task 20761:
[ 3697.940257] kasan_save_track+0x3e/0x80
[ 3697.941782] __kasan_kmalloc+0x72/0x90
[ 3697.943228] __kvmalloc_node_noprof+0x3e9/0x6a0
[ 3697.944948] handle_generic_event+0x59b/0x750
[ 3697.946592] genl_family_rcv_msg_doit+0x3d6/0x560
[ 3697.946977] genl_rcv_msg+0x67c/0x900
[ 3697.947224] netlink_rcv_skb+0x286/0x580
[ 3697.947488] genl_rcv+0x2d/0x80
[ 3
---truncated---
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in the Linux kernel's ksmbd subsystem represents a critical out-of-bounds read condition arising from improper validation of user-supplied data lengths prior to memory access. The flaw is located within the inter-process communication mechanism that facilitates interaction between the userspace ksmbd daemon and the kernel module handling SMB/CIFS protocol operations. Specifically, the function ipc_validate_msg() is responsible for parsing response structures received from the userspace component. This function attempts to extract critical fields such as payload size, session key length, and group counts directly from a buffer provided by the user space application. The fundamental technical error lies in the sequence of operations: the kernel reads these integer values from the buffer before verifying that the allocated memory region is sufficiently large to contain the entire struct associated with those fields. Consequently, if the userspace daemon provides a response message that is truncated or smaller than expected, the pointer arithmetic used to access specific structure members results in reading data beyond the bounds of the allocated slab object.
The root cause of this issue stems from how handle_response() manages memory allocation for incoming netlink attributes. This function sizes the entry->response buffer based solely on the length attribute provided by the netlink protocol, without performing additional sanity checks to ensure the content matches the expected structural layout. In scenarios where a malicious or buggy userspace process sends an RPC request with a minimal payload size, such as one that fits within a small kmalloc-8 cache object, the kernel proceeds to cast this short buffer into a struct ksmbd_rpc_command structure. Because the actual allocated memory is smaller than the sizeof(struct ksmbd_rpc_command), accessing fields like payload_sz at offset eight triggers an out-of-bounds read. This behavior was confirmed through Kernel Address Sanitizer (KASAN) reports, which detected reads of four bytes from addresses outside the valid allocation range during the execution of ipc_msg_send_request().
From a security perspective, this vulnerability is classified under CWE-125: Out-of-bounds Read and aligns with ATT&CK technique T1078: Valid Accounts if exploited by an authenticated attacker. While the immediate manifestation described in the kernel logs indicates a crash or memory corruption warning via KASAN, out-of-bounds reads can have severe operational impacts beyond simple denial of service. An attacker could potentially use this flaw to leak sensitive kernel memory contents, such as stack pointers, cryptographic keys, or other process data residing adjacent to the allocated slab object. This information disclosure could facilitate further exploitation steps, including bypassing security mitigations like KASLR (Kernel Address Space Layout Randomization). Furthermore, if the read values influence subsequent control flow decisions without proper validation, it may lead to arbitrary code execution conditions where an attacker gains kernel-level privileges on the affected system.
The operational impact of this vulnerability is significant for any deployment utilizing ksmbd, particularly in environments where userspace daemons interact with the kernel over netlink sockets. Since ksmbd allows Linux systems to act as SMB servers, exposing this interface without proper input validation creates a remote attack surface if the daemon accepts connections from untrusted networks or compromised clients. The vulnerability affects system stability and integrity, potentially leading to kernel panics that disrupt service availability for all users on the host machine. In cloud or containerized environments, such instability could impact neighboring workloads sharing the same physical infrastructure, thereby widening the blast radius of a successful exploitation attempt.
To mitigate this risk, it is imperative to apply the upstream Linux kernel patch that addresses this issue by enforcing strict length validation before any field dereferencing occurs within ipc_validate_msg(). System administrators should ensure their systems are updated with the latest stable kernel versions containing these fixes. Additionally, defense-in-depth strategies recommend restricting access to netlink sockets used for ksmbd communication through appropriate namespace isolation or firewall rules where feasible. Developers integrating userspace components with this API must implement rigorous input validation checks, ensuring that all length fields correspond accurately to the actual size of the allocated buffers before performing any memory accesses. Regular auditing of kernel interfaces and employing static analysis tools can further help identify similar patterns of unsafe pointer arithmetic in future development cycles.