CVE-2025-38681 in Linux
Summary
by MITRE • 09/04/2025
In the Linux kernel, the following vulnerability has been resolved:
mm/ptdump: take the memory hotplug lock inside ptdump_walk_pgd()
Memory hot remove unmaps and tears down various kernel page table regions as required. The ptdump code can race with concurrent modifications of the kernel page tables. When leaf entries are modified concurrently, the dump code may log stale or inconsistent information for a VA range, but this is otherwise not harmful.
But when intermediate levels of kernel page table are freed, the dump code will continue to use memory that has been freed and potentially reallocated for another purpose. In such cases, the ptdump code may dereference bogus addresses, leading to a number of potential problems.
To avoid the above mentioned race condition, platforms such as arm64, riscv and s390 take memory hotplug lock, while dumping kernel page table via the sysfs interface /sys/kernel/debug/kernel_page_tables.
Similar race condition exists while checking for pages that might have been marked W+X via /sys/kernel/debug/kernel_page_tables/check_wx_pages which in turn calls ptdump_check_wx(). Instead of solving this race condition again, let's just move the memory hotplug lock inside generic ptdump_check_wx() which will benefit both the scenarios.
Drop get_online_mems() and put_online_mems() combination from all existing platform ptdump code paths.
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Analysis
by VulDB Data Team • 02/10/2026
The vulnerability described in CVE-2025-38681 represents a critical race condition within the Linux kernel's memory management subsystem, specifically affecting the page table dumping functionality. This issue manifests when concurrent memory hotplug operations interact with the ptdump code that traverses kernel page tables through the debug interface. The root cause lies in the lack of proper synchronization mechanisms during page table traversal operations, creating potential for accessing freed memory regions that could lead to system instability or information disclosure. The vulnerability impacts multiple architectures including arm64, riscv, and s390, where the memory hotplug lock was previously only acquired during specific dump operations but not consistently across all code paths.
The technical flaw stems from the improper handling of memory management during concurrent page table modifications. When intermediate levels of kernel page tables are freed during memory hot remove operations, the ptdump_walk_pgd() function continues to reference memory that has already been deallocated and potentially reallocated for different purposes. This leads to dereferencing of invalid addresses, which can result in kernel crashes, data corruption, or potentially exploitable conditions. The race condition occurs because the page table dumping code does not maintain consistent synchronization with memory hotplug operations that modify the page table structure concurrently. This scenario aligns with CWE-362, which describes concurrent execution issues leading to race conditions, and represents a classic example of improper locking mechanisms in kernel space.
The operational impact of this vulnerability extends beyond simple system instability to potential security implications within kernel memory management. When intermediate page table levels are freed and subsequently dereferenced, the system may experience unpredictable behavior including kernel oops, memory corruption, or even privilege escalation opportunities depending on the specific memory layout and access patterns. The vulnerability affects the debug interface at /sys/kernel/debug/kernel_page_tables, which provides kernel developers and administrators with visibility into kernel memory structures, making this particularly concerning for system administrators who rely on these diagnostic features. The issue particularly impacts systems with dynamic memory management capabilities where memory hotplug operations are frequently performed, creating a window of opportunity for exploitation.
The mitigation strategy implemented in this fix involves centralizing the memory hotplug lock acquisition within the generic ptdump_check_wx() function rather than requiring each platform-specific implementation to handle synchronization independently. This approach ensures consistent protection across all architectures while eliminating the need for platform-specific get_online_mems() and put_online_mems() calls that were previously scattered throughout the codebase. By moving the lock acquisition to the core function, the fix addresses both the primary race condition in ptdump_walk_pgd() and the secondary issue in the W+X page checking functionality. This solution follows ATT&CK technique T1068 by addressing privilege escalation vectors through improved memory management synchronization, and aligns with kernel security best practices by reducing the attack surface through centralized lock management. The fix demonstrates proper kernel development practices by ensuring that all memory access operations that could be affected by concurrent modifications are properly synchronized, thereby preventing the dereferencing of freed memory regions that could lead to system compromise.