CVE-2025-38689 x86/fpu: Fix NULL dereference in avx512_status()

What is CVE-2025-38689?

CVE-2025-38689 is a medium-severity vulnerability in Linux kernel, published on 4 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

x86/fpu: Fix NULL dereference in avx512_status()

Problem ------- With CONFIG_X86_DEBUG_FPU enabled, reading /proc/[kthread]/arch_status causes a warning and a NULL pointer dereference.

This is because the AVX-512 timestamp code uses x86_task_fpu() but doesn't check it for NULL. CONFIG_X86_DEBUG_FPU addles that function for kernel threads (PF_KTHREAD specifically), making it return NULL.

The point of the warning was to ensure that kernel threads only access task->fpu after going through kernel_fpu_begin()/_end(). Note: all kernel tasks exposed in /proc have a valid task->fpu.

Solution -------- One option is to silence the warning and check for NULL from x86_task_fpu(). However, that warning is fairly fresh and seems like a defense against misuse of the FPU state in kernel threads.

Instead, stop outputting AVX-512_elapsed_ms for kernel threads altogether. The data was garbage anyway because avx512_timestamp is only updated for user threads, not kernel threads.

If anyone ever wants to track kernel thread AVX-512 use, they can come back later and do it properly, separate from this bug fix.

[ dhansen: mostly rewrite changelog ]

Weakness: CWE-476

Which versions are affected by CVE-2025-38689?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2025-38689?

Apply the vendor's patch.

Is CVE-2025-38689 being exploited?

There is no known exploitation of CVE-2025-38689 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2025-38689, GHSA-2j25-8cwq-vgvc, ROOT-OS-UBUNTU-2204-CVE-2025-38689, ROOT-OS-UBUNTU-2404-CVE-2025-38689, UBUNTU-CVE-2025-38689.