CVE-2024-42240
📋 TL;DR
This CVE describes a kernel warning issue in Linux systems with Branch History Injection (BHI) mitigation enabled. When SYSENTER is invoked with the single-step (TF) flag set, the #DB handler issues a warning due to improper timing of BHI clearing operations. This affects Linux systems running vulnerable kernel versions with BHI mitigation enabled.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel warning leading to system instability, potential denial of service through repeated warnings, or system crash in edge cases.
Likely Case
Kernel warning messages in system logs during specific program execution, no direct security compromise.
If Mitigated
No impact when patched or when BHI mitigation is disabled.
🎯 Exploit Status
Proof of concept provided in CVE description demonstrates triggering the warning, but this is not a security exploit - it's a warning/error condition.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions containing fixes from the referenced commits
Vendor Advisory: https://git.kernel.org/stable/c/08518d48e5b744620524f0acd7c26c19bda7f513
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing fixes from referenced commits. 2. Check with your distribution vendor for specific patched kernel versions. 3. Reboot system after kernel update.
🔧 Temporary Workarounds
Disable BHI mitigation
linuxDisable Branch History Injection mitigation (not recommended for security)
echo 0 > /sys/kernel/debug/x86/bhi_enabled
🧯 If You Can't Patch
- Monitor system logs for WARNING messages from exc_debug_kernel
- Restrict local code execution capabilities to prevent triggering the condition
🔍 How to Verify
Check if Vulnerable:
Check kernel version and test with provided PoC: gcc -o sysenter_step sysenter_step.c && ./sysenter_step, then check dmesg for warning messagesCheck Version:
uname -rVerify Fix Applied:
After patching, run the PoC and verify no warning appears in kernel logs📡 Detection & Monitoring
Log Indicators:
- WARNING: CPU: ... at arch/x86/kernel/traps.c:1009 exc_debug_kernel+0xd2/0x160
- Kernel warnings mentioning clear_bhb_loop or BHI
Network Indicators:
- None - local vulnerability only
SIEM Query:
source="kernel" AND "exc_debug_kernel" AND "WARNING" AND "clear_bhb_loop"🔗 References
- https://git.kernel.org/stable/c/08518d48e5b744620524f0acd7c26c19bda7f513
- https://git.kernel.org/stable/c/a765679defe1dc1b8fa01928a6ad6361e72a1364
- https://git.kernel.org/stable/c/ac8b270b61d48fcc61f052097777e3b5e11591e0
- https://git.kernel.org/stable/c/dae3543db8f0cf8ac1a198c3bb4b6e3c24d576cf
- https://git.kernel.org/stable/c/db56615e96c439e13783d7715330e824b4fd4b84
- https://lists.debian.org/debian-lts-announce/2025/01/msg00001.html
