CVE-2025-39904 arm64: kexec: initialize kexec_buf struct in load_other_segments()

What is CVE-2025-39904?

CVE-2025-39904 is a medium-severity vulnerability in Linux kernel, published on 1 Oct 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:

arm64: kexec: initialize kexec_buf struct in load_other_segments()

Patch series "kexec: Fix invalid field access".

The kexec_buf structure was previously declared without initialization. commit bf454ec31add ("kexec_file: allow to place kexec_buf randomly") added a field that is always read but not consistently populated by all architectures. This un-initialized field will contain garbage.

This is also triggering a UBSAN warning when the uninitialized data was accessed:

------------[ cut here ]------------ UBSAN: invalid-load in ./include/linux/kexec.h:210:10 load of value 252 is not a valid value for type '_Bool'

Zero-initializing kexec_buf at declaration ensures all fields are cleanly set, preventing future instances of uninitialized memory being used.

An initial fix was already landed for arm64[0], and this patchset fixes the problem on the remaining arm64 code and on riscv, as raised by Mark.

Discussions about this problem could be found at[1][2].

This patch (of 3):

The kexec_buf structure was previously declared without initialization. commit bf454ec31add ("kexec_file: allow to place kexec_buf randomly") added a field that is always read but not consistently populated by all architectures. This un-initialized field will contain garbage.

This is also triggering a UBSAN warning when the uninitialized data was accessed:

------------[ cut here ]------------ UBSAN: invalid-load in ./include/linux/kexec.h:210:10 load of value 252 is not a valid value for type '_Bool'

Zero-initializing kexec_buf at declaration ensures all fields are cleanly set, preventing future instances of uninitialized memory being used.

Weakness: CWE-908

Which versions are affected by CVE-2025-39904?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2025-39904?

Apply the vendor's patch.

Is CVE-2025-39904 being exploited?

There is no known exploitation of CVE-2025-39904 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-2025-39904, DEBIAN-CVE-2025-39904, GHSA-9j3f-w66p-jqvg, UBUNTU-CVE-2025-39904.