Junglewise Threat Intelligence

CVE-2025-39844: Linux Kernel denial of service via page table sync failure in mm

CVE-2025-39844 · Severity: medium · CVSS 5.5 · Published 2025-09-19

Technologies: Linux Kernel. Vendors: Linux.

Executive brief

A vulnerability in the Linux kernel's memory management system can cause systems to crash during boot or when accessing certain types of memory. This issue primarily affects high-performance servers using large amounts of persistent memory and specific memory paging configurations. An exploit or trigger of this flaw results in a kernel panic, leading to a complete system outage and loss of availability.

Technical details

A race condition or synchronization failure exists in the Linux kernel's memory management (mm) subsystem. When 'vmemmap_can_optimize' returns true, the optimized path in '__populate_section_memmap()' skips the synchronization of top-level Page Global Directory (PGD) entries. This occurs because 'vmemmap_populate_compound_pages()' is implemented in core MM code which historically relied on architecture-specific code to manually handle synchronization. On x86 systems with 4-level paging and large persistent memory, this results in new PGD entries being installed only in 'init_mm.pgd' and not in other active tasks. When a task attempts to access the vmemmap region before synchronization, it triggers a supervisor write access page fault and a subsequent kernel panic. The fix introduces '{pgd,p4d}_populate_kernel()' to ensure explicit synchronization during entry installation.

Affected products

  • Linux Linux Kernel 6.7 to 6.12.46, 6.13 to 6.16.6, 6.17-rc1 to 6.17-rc4

Timeline

  • 2025-08-18: other: Initial patch submitted by Harry Yoo (Oracle)
  • 2025-09-09: patched: Patches committed to stable kernel branches
  • 2025-09-19: advisory: CVE-2025-39844 published

References

Related threats