CVE-2026-23100 mm/hugetlb: fix hugetlb_pmd_shared()

What is CVE-2026-23100?

CVE-2026-23100 is a medium-severity vulnerability in Linux kernel, published on 4 Feb 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/hugetlb: fix hugetlb_pmd_shared()

Patch series "mm/hugetlb: fixes for PMD table sharing (incl. using mmu_gather)", v3.

One functional fix, one performance regression fix, and two related comment fixes.

I cleaned up my prototype I recently shared [1] for the performance fix, deferring most of the cleanups I had in the prototype to a later point. While doing that I identified the other things.

The goal of this patch set is to be backported to stable trees "fairly" easily. At least patch #1 and #4.

Patch #1 fixes hugetlb_pmd_shared() not detecting any sharing Patch #2 + #3 are simple comment fixes that patch #4 interacts with. Patch #4 is a fix for the reported performance regression due to excessive IPI broadcasts during fork()+exit().

The last patch is all about TLB flushes, IPIs and mmu_gather. Read: complicated

There are plenty of cleanups in the future to be had + one reasonable optimization on x86. But that's all out of scope for this series.

Runtime tested, with a focus on fixing the performance regression using the original reproducer [2] on x86.

This patch (of 4):

We switched from (wrongly) using the page count to an independent shared count. Now, shared page tables have a refcount of 1 (excluding speculative references) and instead use ptdesc->pt_share_count to identify sharing.

We didn't convert hugetlb_pmd_shared(), so right now, we would never detect a shared PMD table as such, because sharing/unsharing no longer touches the refcount of a PMD table.

Page migration, like mbind() or migrate_pages() would allow for migrating folios mapped into such shared PMD tables, even though the folios are not exclusive. In smaps we would account them as "private" although they are "shared", and we would be wrongly setting the PM_MMAP_EXCLUSIVE in the pagemap interface.

Fix it by properly using ptdesc_pmd_is_shared() in hugetlb_pmd_shared().

Which versions are affected by CVE-2026-23100?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-23100?

Apply the vendor's patch.

Is CVE-2026-23100 being exploited?

There is no known exploitation of CVE-2026-23100 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-80285, BELL-CVE-2026-23100, DEBIAN-CVE-2026-23100, GHSA-4rhr-9xj2-x9gx, ROOT-OS-DEBIAN-11-CVE-2026-23100, ROOT-OS-DEBIAN-12-CVE-2026-23100 and 4 more.