CVE-2025-39776
📋 TL;DR
A use-after-free vulnerability in the Linux kernel's debug_vm_pgtable test module allows stale page table entries to persist after test completion. When another process allocates memory at the same address, it may encounter corrupted page table entries, potentially leading to kernel crashes or memory corruption. This affects systems with CONFIG_DEBUG_VM_PGTABLE=y enabled in debug kernels.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel panic, system crash, or potential privilege escalation if an attacker can trigger memory corruption leading to arbitrary code execution in kernel context.
Likely Case
Kernel crashes or system instability when debug_vm_pgtable tests run and subsequent processes allocate memory at the same addresses.
If Mitigated
Minimal impact if CONFIG_DEBUG_VM_PGTABLE is disabled or systems are not running debug kernels.
🎯 Exploit Status
Exploitation requires local access, debug kernel configuration, and specific conditions to trigger the stale page table entry issue.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patches available in stable kernel trees (commits: 47d2a149611b8a94d24add9868c442a4af278658, 561171db3b3eb759ba3f284dba7a76f4476ade03, 61a9f2e5c49f05e3ea2c16674540a075a1b4be6f, 63962ff932ef359925b94be2a88df6b4fd4fed0a, 7bf57a0709cd7c9088cea8de023d6f4fbf2518b0)
Vendor Advisory: https://git.kernel.org/stable/c/47d2a149611b8a94d24add9868c442a4af278658
Restart Required: Yes
Instructions:
1. Update to a patched kernel version from your distribution vendor. 2. Rebuild kernel if using custom kernel with CONFIG_DEBUG_VM_PGTABLE=y. 3. Reboot system to load new kernel.
🔧 Temporary Workarounds
Disable debug_vm_pgtable module
linuxDisable CONFIG_DEBUG_VM_PGTABLE in kernel configuration to prevent the vulnerable code from being compiled.
# Reconfigure kernel with CONFIG_DEBUG_VM_PGTABLE=n
# Rebuild and install kernel
Avoid debug kernels in production
linuxUse production kernels without debug options enabled instead of debug kernels.
🧯 If You Can't Patch
- Ensure production systems are not running debug kernels with CONFIG_DEBUG_VM_PGTABLE=y
- Restrict access to systems with debug kernels to trusted users only
🔍 How to Verify
Check if Vulnerable:
Check kernel config: grep CONFIG_DEBUG_VM_PGTABLE /boot/config-$(uname -r) or /proc/config.gz. If 'y' and kernel version is unpatched, system is vulnerable.Check Version:
uname -rVerify Fix Applied:
Check kernel version is patched and CONFIG_DEBUG_VM_PGTABLE is either 'n' or kernel includes the fix commits.📡 Detection & Monitoring
Log Indicators:
- Kernel warnings about 'Bad rss-counter state'
- Warnings about 'non-zero pgtables_bytes on freeing mm'
- Kernel panics or crashes after debug_vm_pgtable tests
SIEM Query:
kernel:WARNING AND ("Bad rss-counter state" OR "non-zero pgtables_bytes on freeing mm")🔗 References
- https://git.kernel.org/stable/c/47d2a149611b8a94d24add9868c442a4af278658
- https://git.kernel.org/stable/c/561171db3b3eb759ba3f284dba7a76f4476ade03
- https://git.kernel.org/stable/c/61a9f2e5c49f05e3ea2c16674540a075a1b4be6f
- https://git.kernel.org/stable/c/63962ff932ef359925b94be2a88df6b4fd4fed0a
- https://git.kernel.org/stable/c/7bf57a0709cd7c9088cea8de023d6f4fbf2518b0
- https://git.kernel.org/stable/c/dde30854bddfb5d69f30022b53c5955a41088b33
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
