CVE-2026-74712 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
vdpa/mlx5: Fix buffer length in create_direct_keys()
We have seen in our CI the following KASAN message: BUG: KASAN: slab-out-of-bounds in cmd_exec+0x550/0xca0 [mlx5_core]
Read of size 272 at addr 0000000176795020 by task qemu-system-s39/82764 [...]
[<000011388ab3a7a0>] cmd_exec+0x550/0xca0 [mlx5_core]
[<000011388ab3b61c>] mlx5_cmd_exec_cb+0x25c/0x4f0 [mlx5_core]
[<000011388b21e82e>] mlx5_vdpa_exec_async_cmds+0x22e/0x5e0 [mlx5_vdpa]
[<000011388b21fd44>] create_direct_keys+0x954/0xef0 [mlx5_vdpa]
[...]
The buggy address is located 4128 bytes inside of allocated 4384-byte region [0000000176794000, 0000000176795120)
So in essence we read 16 bytes beyond 4384-byte allocation. create_direct_keys calculates the pointer and length for in and out buffers. The size calculation for in includes the entire structure size (out + in + mtt[]) but the pointer passed to cmd_exec points only
to the 'in' field, skipping the 'out' field.
This causes mlx5_copy_to_msg() to read beyond the allocated buffer by sizeof(out) bytes when copying command data.
Properly calculate the input size to match the pointer and allocation size.
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Analysis
by VulDB Data Team • 08/22/2026
The vulnerability identified in the Linux kernel's Virtual Data Path Accelerator (vdpa) subsystem, specifically within the mlx5 driver module, represents a critical memory safety flaw rooted in incorrect buffer length calculations during command execution. This issue manifests as an out-of-bounds read operation that can be triggered by user-space applications interacting with virtualized hardware resources. The root cause lies in the create_direct_keys function, which is responsible for preparing input and output buffers for communication between the kernel driver and the underlying Mellanox ConnectX hardware via the mlx5_core interface. During this preparation phase, the code calculates the total size of a command structure that includes both an out buffer and an in buffer along with associated memory translation table entries. However, while the allocation logic correctly accounts for the combined size of these components, the pointer passed to the subsequent cmd_exec function is offset incorrectly. Specifically, the pointer targets only the 'in' field of the structure, effectively skipping over the preceding 'out' field data that was also allocated in the same contiguous memory block.
This misalignment between the calculated buffer length and the actual starting address of the data being accessed leads to a significant discrepancy during command execution. When mlx5_copy_to_msg is invoked to copy command data into the message structure for hardware processing, it relies on the size parameter provided by create_direct_keys. Because this size reflects the total allocation including the skipped 'out' section, but the pointer starts at the beginning of the 'in' section, the function attempts to read bytes that reside beyond the intended boundary of the accessible data region relative to the current pointer position. In observed instances within continuous integration environments using QEMU for s390 architecture emulation, this resulted in a Kernel Address Sanitizer (KASAN) report indicating a slab-out-of-bounds error where 272 bytes were read from an address located well beyond the allocated 4384-byte region. The specific offset indicates that approximately sixteen bytes or more of unintended memory are being accessed, depending on the exact structure layout and command parameters involved in each execution instance.
From a security perspective, this vulnerability falls under CWE-125: Out-of-bounds Read, which describes situations where software reads data from outside the bounds of an allocated buffer. The operational impact of such a flaw can vary significantly based on memory state at the time of exploitation. While immediate denial of service is a likely outcome due to kernel panic or oops triggered by accessing invalid memory pages, more severe consequences are possible if the out-of-bounds read exposes sensitive kernel data structures to user-space processes like QEMU. An attacker with local access could potentially leverage this information leak to gather cryptographic keys, network configuration details, or other privileged system state that resides in adjacent memory regions. Furthermore, depending on how the leaked data influences subsequent control flow or if combined with other vulnerabilities, it might contribute to privilege escalation scenarios where a low-privileged user gains higher-level permissions within the virtualization host environment.
The technical execution of this exploit aligns with techniques observed in ATT&CK framework mappings related to unauthorized access and information discovery through memory corruption flaws. Although primarily an out-of-bounds read rather than a write, such vulnerabilities are often precursors to more complex exploitation chains involving heap spraying or precise memory layout manipulation. The flaw exists within the mlx5_vdpa module, which interfaces with virtualized network devices, meaning that any workload utilizing this specific hardware acceleration path is potentially vulnerable. This includes cloud instances and enterprise deployments relying on Mellanox NICs for high-performance networking via vdpa interfaces.
Mitigation strategies must focus on correcting the pointer arithmetic and buffer size calculations within the create_direct_keys function. The primary fix involves ensuring that the input size parameter passed to cmd_exec accurately reflects the distance from the current pointer position to the end of the valid data region, rather than using a total allocation size that includes skipped fields. Developers should implement strict bounds checking during buffer preparation phases in kernel drivers handling hardware commands. Additionally, enabling KASAN and other memory error detection tools in development environments is crucial for early identification of such alignment issues before they reach production kernels. System administrators running affected versions should apply the latest available kernel patches provided by their distribution vendors to resolve this specific logic error in the mlx5 driver stack. Regular auditing of pointer arithmetic in low-level hardware interaction code remains essential to prevent similar off-by-one or offset miscalculations that compromise memory safety guarantees within the operating system core.