# CVE-2021-46927: nitro_enclaves: Use get_user_pages_unlocked() call to handle mmap assert

> A local attacker can trigger a kernel bug in the Nitro Enclaves driver, causing a system crash and denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 27 Feb 2024
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2021-46927, GHSA-4f2m-qf8w-84rw, UBUNTU-CVE-2021-46927

## What is CVE-2021-46927?

CVE-2021-46927 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 Feb 2024. 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:

nitro_enclaves: Use get_user_pages_unlocked() call to handle mmap assert

After commit 5b78ed24e8ec ("mm/pagemap: add mmap_assert_locked()
annotations to find_vma*()"), the call to get_user_pages() will trigger
the mmap assert.

static inline void mmap_assert_locked(struct mm_struct *mm)
{
	lockdep_assert_held(&mm->mmap_lock);
	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
}

[   62.521410] kernel BUG at include/linux/mmap_lock.h:156!
...........................................................
[   62.538938] RIP: 0010:find_vma+0x32/0x80
...........................................................
[   62.605889] Call Trace:
[   62.608502]  <TASK>
[   62.610956]  ? lock_timer_base+0x61/0x80
[   62.614106]  find_extend_vma+0x19/0x80
[   62.617195]  __get_user_pages+0x9b/0x6a0
[   62.620356]  __gup_longterm_locked+0x42d/0x450
[   62.623721]  ? finish_wait+0x41/0x80
[   62.626748]  ? __kmalloc+0x178/0x2f0
[   62.629768]  ne_set_user_memory_region_ioctl.isra.0+0x225/0x6a0 [nitro_enclaves]
[   62.635776]  ne_enclave_ioctl+0x1cf/0x6d7 [nitro_enclaves]
[   62.639541]  __x64_sys_ioctl+0x82/0xb0
[   62.642620]  do_syscall_64+0x3b/0x90
[   62.645642]  entry_SYSCALL_64_after_hwframe+0x44/0xae

Use get_user_pages_unlocked() when setting the enclave memory regions.
That's a similar pattern as mmap_read_lock() used together with
get_user_pages().

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2021-46927?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-46927?

Apply the vendor's patch.

## Is CVE-2021-46927 being exploited?

There is no known exploitation of CVE-2021-46927 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-46927 and fix it if it is affected.

What it is: CVE-2021-46927 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 Feb 2024. 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-2021-46927 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2021-46927/ (Markdown: https://insights.sbomify.com/CVE-2021-46927/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-46927
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-46927
- OSV: https://osv.dev/vulnerability/CVE-2021-46927

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-46927/
Summaries are generated and may contain mistakes; the official description above is the record.