CVE-2025-39904
📋 TL;DR
This CVE describes an uninitialized memory vulnerability in the Linux kernel's kexec functionality on arm64 and riscv architectures. The uninitialized field in the kexec_buf structure could contain garbage values that might be interpreted incorrectly during kexec operations. This affects Linux systems using kexec on arm64 or riscv architectures.
💻 Affected Systems
- Linux kernel
📦 What is this software?
Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →⚠️ Risk & Real-World Impact
Worst Case
Potential kernel panic or system crash during kexec operations, possibly leading to denial of service or unpredictable system behavior.
Likely Case
UBSAN warnings during kernel boot or kexec operations, with potential for system instability if the garbage values trigger unexpected behavior.
If Mitigated
Minor performance impact from UBSAN checks with no security or stability consequences.
🎯 Exploit Status
Exploitation requires root privileges to trigger kexec operations. The vulnerability primarily causes UBSAN warnings and potential instability rather than providing attacker-controlled memory corruption.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions containing commits 04d3cd43700a2d0fe4bfb1012a8ec7f2e34a3507 and 340cc9a3bd30b25edaf6a9708d41b5f2c10a054a
Vendor Advisory: https://git.kernel.org/stable/c/04d3cd43700a2d0fe4bfb1012a8ec7f2e34a3507
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix commits. 2. Reboot system to load new kernel. 3. For distributions: Use package manager (apt/yum/dnf) to update kernel package.
🔧 Temporary Workarounds
Disable kexec functionality
linuxPrevent use of kexec system call to avoid triggering the vulnerability
echo 0 > /proc/sys/kernel/kexec_load_disabled
sysctl -w kernel.kexec_load_disabled=1
🧯 If You Can't Patch
- Disable kexec functionality using sysctl or kernel parameters
- Implement strict access controls to prevent unauthorized users from executing kexec operations
🔍 How to Verify
Check if Vulnerable:
Check kernel version and architecture: uname -r and uname -m. If arm64 or riscv architecture and kernel version predates fix commits, system may be vulnerable.Check Version:
uname -rVerify Fix Applied:
Check kernel version contains fix commits: grep -q '04d3cd43700a2d0fe4bfb1012a8ec7f2e34a3507\|340cc9a3bd30b25edaf6a9708d41b5f2c10a054a' /proc/version_signature or verify with distribution's package manager.📡 Detection & Monitoring
Log Indicators:
- UBSAN warnings in kernel logs: 'UBSAN: invalid-load in ./include/linux/kexec.h'
- Kernel panic or crash during kexec operations
Network Indicators:
- None - this is a local kernel vulnerability
SIEM Query:
source="kernel" AND ("UBSAN" AND "kexec" OR "kexec_buf")