CVE-2025-38084 mm/hugetlb: unshare page tables during VMA split, not before
A race condition in Linux kernel hugetlb page table unsharing during VMA splits allows attackers to potentially escalate privileges or execute code.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-38084?
CVE-2025-38084 is a high-severity vulnerability in Debian Debian Linux, published on 28 Jun 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
mm/hugetlb: unshare page tables during VMA split, not before
Currently, __split_vma() triggers hugetlb page table unsharing through vm_ops->may_split(). This happens before the VMA lock and rmap locks are taken - which is too early, it allows racing VMA-locked page faults in our process and racing rmap walks from other processes to cause page tables to be shared again before we actually perform the split.
Fix it by explicitly calling into the hugetlb unshare logic from __split_vma() in the same place where THP splitting also happens. At that point, both the VMA and the rmap(s) are write-locked.
An annoying detail is that we can now call into the helper hugetlb_unshare_pmds() from two different locking contexts:
1. from hugetlb_split(), holding: - mmap lock (exclusively) - VMA lock - file rmap lock (exclusively) 2. hugetlb_unshare_all_pmds(), which I think is designed to be able to call us with only the mmap lock held (in shared mode), but currently only runs while holding mmap lock (exclusively) and VMA lock
Backporting note: This commit fixes a racy protection that was introduced in commit b30c14cd6102 ("hugetlb: unshare some PMDs when splitting VMAs"); that commit claimed to fix an issue introduced in 5.13, but it should actually also go all the way back.
[[email protected]: v2]
Which versions are affected by CVE-2025-38084?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-38084?
Apply the vendor's patch.
Is CVE-2025-38084 being exploited?
There is no known exploitation of CVE-2025-38084 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as AZL-64377, BELL-CVE-2025-38084, DEBIAN-CVE-2025-38084, GHSA-mfp4-4cfm-v388, ROOT-OS-DEBIAN-11-CVE-2025-38084, ROOT-OS-DEBIAN-12-CVE-2025-38084 and 3 more.