CVE-2026-31575 mm/userfaultfd: fix hugetlb fault mutex hash calculation
A race condition in the Linux kernel's userfaultfd hugetlb handling can corrupt reservation maps, leading to a system crash via BUG_ON.
- 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-2026-31575?
CVE-2026-31575 is a medium-severity vulnerability in Linux kernel, published on 24 Apr 2026. 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/userfaultfd: fix hugetlb fault mutex hash calculation
In mfill_atomic_hugetlb(), linear_page_index() is used to calculate the page index for hugetlb_fault_mutex_hash(). However, linear_page_index() returns the index in PAGE_SIZE units, while hugetlb_fault_mutex_hash() expects the index in huge page units. This mismatch means that different addresses within the same huge page can produce different hash values, leading to the use of different mutexes for the same huge page. This can cause races between faulting threads, which can corrupt the reservation map and trigger the BUG_ON in resv_map_release().
Fix this by introducing hugetlb_linear_page_index(), which returns the page index in huge page granularity, and using it in place of linear_page_index().
Which versions are affected by CVE-2026-31575?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31575?
Apply the vendor's patch.
Is CVE-2026-31575 being exploited?
There is no known exploitation of CVE-2026-31575 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-83792, BELL-CVE-2026-31575, DEBIAN-CVE-2026-31575, GHSA-2cxr-hf6j-p3mc, ROOT-OS-DEBIAN-11-CVE-2026-31575, ROOT-OS-DEBIAN-12-CVE-2026-31575 and 3 more.