CVE-2026-53173: Linux Kernel Ethos-U Out-of-Bounds Write Privilege Escalation

Technical summary

CVE-2026-53173 is an out-of-bounds (OOB) write vulnerability in accel/ethosu within the Linux kernel. The ethosu_gem_cmdstream_copy_and_validate() function parses command streams into a DMA-allocated buffer (bocmds) of exactly size bytes, providing valid indices from 0 to size/4−1. The parsing loop iterates i from 0 to size/4−1, and when bit 14 is set in a command word (indicating a 64-bit command), the index i is incremented and a second write is performed without re-checking the loop bound. When i equals size/4−1 at loop entry and bit 14 is set, the second write at bocmds[i] (after incrementing to size/4) exceeds the allocation by four bytes. Both buffer contents and size are user-controlled via ioctl, making this a direct userspace-triggerable heap overflow.

Business impact

This vulnerability enables local privilege escalation on systems running vulnerable Linux kernels with the Ethos-U accelerator driver. An unprivileged local user can corrupt kernel heap memory, potentially gaining root access or causing denial of service. The impact is elevated because the vulnerability affects security-critical kernel memory management and can be reliably triggered. For organizations running GPU-accelerated or ML-accelerated workloads on Linux systems, this represents a significant privilege escalation risk that could undermine kernel isolation guarantees.

Affected systems

The Linux kernel versions containing this vulnerability are those with the accel/ethosu driver. Affected platforms include systems using Arm Ethos-U neural processing units. Verify your kernel version against the vendor advisory to determine exact patch boundaries. Typically, systems running recent kernel versions (5.10+) without the specific patch are at risk.

Exploitability

Exploitability is straightforward from the local context. An unprivileged local user with access to the Ethos-U device (/dev/ethosu or similar) can trigger the vulnerability by issuing a specially crafted ioctl with a command buffer where the final command word has bit 14 set. No elevated privileges, user interaction, or complex environment setup is required beyond local system access. The vulnerability is not exposed remotely unless the system permits unprivileged local code execution.

Remediation

Apply the Linux kernel patch that adds bounds checking for the incremented index before the second write in ethosu_gem_cmdstream_copy_and_validate(). The fix verifies that i+1 remains within bounds when a 64-bit command is detected and returns -EINVAL if the buffer is too small. Consult your Linux distribution's security advisory or the upstream kernel repository for the specific patch version addressing this issue.

Patch guidance

Check your current kernel version against the Linux kernel security advisory for CVE-2026-53173. Most distributions (Red Hat, Debian, Ubuntu, SUSE, etc.) will backport the bounds-checking fix to their supported kernel branches. Update to the patched kernel version recommended by your distribution, typically available through standard package management (yum, apt, zypper). After patching, verify the fix is present by confirming the bounds check in the accel/ethosu driver code or monitoring kernel changelogs.

Detection guidance

Monitor kernel logs for failed ioctl calls with -EINVAL returns on the Ethos-U device. Detection tools should focus on: (1) unauthorized access attempts to /dev/ethosu or equivalent device nodes by unprivileged users; (2) command stream parsing errors in kernel logs; (3) heap corruption detectors (if available) that identify out-of-bounds writes in DMA-allocated memory. Kernel Address Sanitizer (KASAN) or similar runtime checkers will catch exploitation attempts if enabled. Network-based detection is not applicable as the vulnerability is local only.

Why prioritize this

This vulnerability merits immediate attention due to its HIGH CVSS score (7.8) reflecting local privilege escalation capability, CWE-787 (out-of-bounds write) classification, and reliable exploitability by unprivileged users. The kernel is a critical attack surface, and heap corruption leading to privilege escalation is a fundamental security failure. Organizations should prioritize patching systems that expose Ethos-U devices to untrusted local users.

Risk score, explained

The CVSS 3.1 score of 7.8 (HIGH) reflects: Attack Vector Local (narrow exposure surface but still significant), Attack Complexity Low (straightforward trigger), Privilege Required Low (unprivileged user sufficient), User Interaction None (automatic), Scope Unchanged, and high impact on Confidentiality, Integrity, and Availability. The score appropriately captures the severity of a local heap overflow in kernel memory leading to privilege escalation. The absence of a KEV entry indicates this was not yet publicly exploited at the time of advisory publication, but the technical tractability and local access model suggest risk.

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