CVE-2025-39992 Affecting kernel-64k-debug package, versions *


Severity

Recommended
medium

Based on CentOS security rating.

Threat Intelligence

EPSS
0.02% (4th percentile)

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  • Snyk IDSNYK-CENTOS9-KERNEL64KDEBUG-13590152
  • published17 Oct 2025
  • disclosed15 Oct 2025

Introduced: 15 Oct 2025

NewCVE-2025-39992  (opens in a new tab)

How to fix?

There is no fixed version for Centos:9 kernel-64k-debug.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-64k-debug package and not the kernel-64k-debug package as distributed by Centos. See How to fix? for Centos:9 relevant fixed versions and status.

In the Linux kernel, the following vulnerability has been resolved:

mm: swap: check for stable address space before operating on the VMA

It is possible to hit a zero entry while traversing the vmas in unuse_mm() called from swapoff path and accessing it causes the OOPS:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000446--> Loading the memory from offset 0x40 on the XA_ZERO_ENTRY as address. Mem abort info: ESR = 0x0000000096000005 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x05: level 1 translation fault

The issue is manifested from the below race between the fork() on a process and swapoff: fork(dup_mmap()) swapoff(unuse_mm)


  1. Identical mtree is built using __mt_dup().

  2. copy_pte_range()--> copy_nonpresent_pte(): The dst mm is added into the mmlist to be visible to the swapoff operation.

  3. Fatal signal is sent to the parent process(which is the current during the fork) thus skip the duplication of the vmas and mark the vma range with XA_ZERO_ENTRY as a marker for this process that helps during exit_mmap().

                  4) swapoff is tried on the
                 'mm' added to the 'mmlist' as
                 part of the 2.
    
    
              5) unuse_mm(), that iterates
             through the vma's of this 'mm'
             will hit the non-NULL zero entry
             and operating on this zero entry
             as a vma is resulting into the
             oops.
    

The proper fix would be around not exposing this partially-valid tree to others when droping the mmap lock, which is being solved with [1]. A simpler solution would be checking for MMF_UNSTABLE, as it is set if mm_struct is not fully initialized in dup_mmap().

Thanks to Liam/Lorenzo/David for all the suggestions in fixing this issue.

CVSS Base Scores

version 3.1