# CVE-2026-74518: mm/hugetlb: fix list corruption in allocate_file_region_entries()

> A race condition in Linux kernel hugetlb memory management causes list corruption and use-after-free, allowing local attackers to crash the system or execute code.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-96360, BELL-CVE-2026-74518, DEBIAN-CVE-2026-74518, GHSA-9v2f-674j-mrjw, UBUNTU-CVE-2026-74518

## What is CVE-2026-74518?

CVE-2026-74518 is a high-severity use after free vulnerability in Linux, published on 15 Aug 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 list corruption in allocate_file_region_entries()

allocate_file_region_entries() tops up resv->region_cache with freshly
allocated file_region descriptors.  The allocation uses GFP_KERNEL, so
resv->lock is dropped around it: the new entries are gathered on a
stack-local list head, allocated_regions, and spliced into
resv->region_cache once the lock is re-acquired.

The splice used list_splice(), which moves the entries but does not
re-initialize the source head, so allocated_regions is left pointing at an
entry that now lives on resv->region_cache.  The top-up runs in a while
loop that re-checks the cache deficit after re-acquiring the lock.  For a
shared mapping the resv_map is shared by every mapper of the hugetlbfs
inode, so a concurrent region_chg()/region_add()/region_del() on the same
resv_map can consume cache entries during the unlocked window and force a
second iteration.  That iteration calls list_add() on the stale head and
corrupts the list; with CONFIG_DEBUG_LIST the __list_add_valid() check
trips:

  list_add corruption. next->prev should be prev (ffffc900011ff7f8),
  but was ffff88814c281460. (next=ffff88814c545640).
  kernel BUG at lib/list_debug.c:31!
   allocate_file_region_entries+0x191/0x420
   region_chg+0x267/0x300
   hugetlb_reserve_pages+0x387/0xc80
   hugetlbfs_file_mmap+0x2ce/0x3f0
   mmap_region+0x1348/0x1a80
   do_mmap+0x85e/0xb90
   vm_mmap_pgoff+0x18c/0x330
   ksys_mmap_pgoff+0x2a1/0x3e0
   do_syscall_64+0xd7/0x420

Without CONFIG_DEBUG_LIST the bad list_add() silently links a kernel-stack
address into resv->region_cache, leading to later use-after-free.

This was observed as a real host panic on a dense KVM host where a QEMU
guest-RAM hugetlbfs file was mapped MAP_SHARED by both QEMU and a separate
SPDK/DPDK vhost-user target, generating concurrent region_* traffic on one
shared resv_map.

Use list_splice_init() so the source head is re-initialized empty after
each splice, making the retry loop safe.

## Which versions are affected by CVE-2026-74518?


## How do I fix CVE-2026-74518?

Apply the vendor's patch.

## Is CVE-2026-74518 being exploited?

There is no known exploitation of CVE-2026-74518 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74518 and fix it if it is affected.

What it is: CVE-2026-74518 is a high-severity use after free vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74518 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-74518/ (Markdown: https://insights.sbomify.com/CVE-2026-74518/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74518
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74518
- OSV: https://osv.dev/vulnerability/CVE-2026-74518

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74518/
Summaries are generated and may contain mistakes; the official description above is the record.