CVE-2025-39992
Vulnerability Scoring
Status: Received on 15 Oct 2025, 08:15 UTC
Published on: 15 Oct 2025, 08:15 UTC
CVSS Release:
CVE-2025-39992: 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.
The exploitability of CVE-2025-39992 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).
No exploitability data is available for CVE-2025-39992.
A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.
Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.
Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.
Above is the CVSS Sub-score Breakdown for CVE-2025-39992, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.
Below is the Impact Analysis for CVE-2025-39992, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.
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