CVE-2025-40300
📋 TL;DR
VMSCAPE is a vulnerability in the Linux kernel that allows a malicious guest VM to poison branch predictors, potentially enabling speculative execution attacks against userspace hypervisors like QEMU. This affects systems running Linux kernels with x86 virtualization features where untrusted guests could exploit insufficient branch predictor isolation.
💻 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 →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 →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
A malicious guest VM could perform speculative execution attacks against the hypervisor's userspace components, potentially leaking sensitive data or compromising the host system.
Likely Case
Information disclosure through side-channel attacks, though exploitation requires specific conditions and may be limited by existing mitigations.
If Mitigated
With proper mitigations applied, the risk is significantly reduced to acceptable levels with minimal performance impact.
🎯 Exploit Status
Exploitation requires guest VM access and knowledge of speculative execution techniques
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel versions containing commits 15006289e5c38b2a830e1fba221977a27598176c and related
Vendor Advisory: https://git.kernel.org/stable/c/15006289e5c38b2a830e1fba221977a27598176c
Restart Required: No
Instructions:
1. Update Linux kernel to version containing the fix commits. 2. For distributions: Use package manager (apt/yum/dnf) to update kernel package. 3. Reboot if kernel update requires it (check distribution guidelines).
🔧 Temporary Workarounds
Disable vulnerable virtualization features
x86Disable VMSCAPE-affected virtualization features if not required
echo 0 > /sys/module/kvm_intel/parameters/vmentry_l1d_flush
echo 0 > /sys/module/kvm/parameters/vmentry_l1d_flush
🧯 If You Can't Patch
- Isolate virtualization hosts from sensitive systems
- Implement strict access controls for guest VM creation and management
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if virtualization features are enabled: grep -q vmentry_l1d_flush /sys/module/kvm*/parameters/* 2>/dev/null && echo 'Potentially vulnerable'Check Version:
uname -rVerify Fix Applied:
Verify kernel version contains fix commits: uname -r and check with distribution vendor for patched versions📡 Detection & Monitoring
Log Indicators:
- Unusual VM exit patterns
- Increased branch misprediction rates in performance monitoring
Network Indicators:
- Not network exploitable
SIEM Query:
Not applicable - local exploitation only🔗 References
- https://git.kernel.org/stable/c/15006289e5c38b2a830e1fba221977a27598176c
- https://git.kernel.org/stable/c/2f4f2f8f860cb4c3336a7435ebe8dcfded0c9c6e
- https://git.kernel.org/stable/c/2f8f173413f1cbf52660d04df92d0069c4306d25
- https://git.kernel.org/stable/c/34e5667041050711a947e260fc9ebebe08bddee5
- https://git.kernel.org/stable/c/459274c77b37ac63b78c928b4b4e748d1f9d05c8
- https://git.kernel.org/stable/c/510603f504796c3535f67f55fb0b124a303b44c8
- https://git.kernel.org/stable/c/893387c18612bb452336a5881da0d015a7e8f4a2
- https://git.kernel.org/stable/c/9c23a90648e831d611152ac08dbcd1283d405e7f
- https://git.kernel.org/stable/c/ac60717f9a8d21c58617d0b34274babf24135835
- https://git.kernel.org/stable/c/c08192b5d6730a914dee6175bc71092ee6a65f14
- https://git.kernel.org/stable/c/d5490dfa35427a2967e00a4c7a1b95fdbc8ede34
- https://git.kernel.org/stable/c/d7ddc93392e4a7ffcccc86edf6ef3e64c778db52
- https://git.kernel.org/stable/c/f866eef8d1c65504d30923c3f14082ad294d0e6d
- http://www.openwall.com/lists/oss-security/2025/11/14/3
- http://www.openwall.com/lists/oss-security/2025/11/14/4
- http://www.openwall.com/lists/oss-security/2025/11/14/6
- http://www.openwall.com/lists/oss-security/2025/11/17/2
- http://www.openwall.com/lists/oss-security/2025/11/17/3
- https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
