CVE-2026-43331 x86/kexec: Disable KCOV instrumentation after load_segments()

What is CVE-2026-43331?

CVE-2026-43331 is a medium-severity denial of service vulnerability in Linux kernel, published on 8 May 2026. 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/kexec: Disable KCOV instrumentation after load_segments()

The load_segments() function changes segment registers, invalidating GS base (which KCOV relies on for per-cpu data). When CONFIG_KCOV is enabled, any subsequent instrumented C code call (e.g. native_gdt_invalidate()) begins crashing the kernel in an endless loop.

To reproduce the problem, it's sufficient to do kexec on a KCOV-instrumented kernel:

$ kexec -l /boot/otherKernel $ kexec -e

The real-world context for this problem is enabling crash dump collection in syzkaller. For this, the tool loads a panic kernel before fuzzing and then calls makedumpfile after the panic. This workflow requires both CONFIG_KEXEC and CONFIG_KCOV to be enabled simultaneously.

Adding safeguards directly to the KCOV fast-path (__sanitizer_cov_trace_pc()) is also undesirable as it would introduce an extra performance overhead.

Disabling instrumentation for the individual functions would be too fragile, so disable KCOV instrumentation for the entire machine_kexec_64.c and physaddr.c. If coverage-guided fuzzing ever needs these components in the future, other approaches should be considered.

The problem is not relevant for 32 bit kernels as CONFIG_KCOV is not supported there.

[ bp: Space out comment for better readability. ]

Which versions are affected by CVE-2026-43331?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-43331?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-43331 being exploited?

There is no known exploitation of CVE-2026-43331 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-2026-43331, DEBIAN-CVE-2026-43331, GHSA-9w3c-wc93-j4jx, ROOT-OS-DEBIAN-13-CVE-2026-43331, ROOT-OS-UBUNTU-2404-CVE-2026-43331, UBUNTU-CVE-2026-43331.