# CVE-2021-47376: bpf: Add oversize check before call kvcalloc()

> A missing size check in the Linux kernel BPF verifier can trigger a kernel warning and potential denial of service when loading oversized BTF information.

- **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:** 21 May 2024
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2021-47376, GHSA-p793-3f2h-38xw, UBUNTU-CVE-2021-47376

## What is CVE-2021-47376?

CVE-2021-47376 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 May 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:

bpf: Add oversize check before call kvcalloc()

Commit 7661809d493b ("mm: don't allow oversized kvmalloc() calls") add the
oversize check. When the allocation is larger than what kmalloc() supports,
the following warning triggered:

WARNING: CPU: 0 PID: 8408 at mm/util.c:597 kvmalloc_node+0x108/0x110 mm/util.c:597
Modules linked in:
CPU: 0 PID: 8408 Comm: syz-executor221 Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:kvmalloc_node+0x108/0x110 mm/util.c:597
Call Trace:
 kvmalloc include/linux/mm.h:806 [inline]
 kvmalloc_array include/linux/mm.h:824 [inline]
 kvcalloc include/linux/mm.h:829 [inline]
 check_btf_line kernel/bpf/verifier.c:9925 [inline]
 check_btf_info kernel/bpf/verifier.c:10049 [inline]
 bpf_check+0xd634/0x150d0 kernel/bpf/verifier.c:13759
 bpf_prog_load kernel/bpf/syscall.c:2301 [inline]
 __sys_bpf+0x11181/0x126e0 kernel/bpf/syscall.c:4587
 __do_sys_bpf kernel/bpf/syscall.c:4691 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:4689 [inline]
 __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:4689
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

## Which versions are affected by CVE-2021-47376?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47376?

Apply the vendor's patch.

## Is CVE-2021-47376 being exploited?

There is no known exploitation of CVE-2021-47376 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-2021-47376 and fix it if it is affected.

What it is: CVE-2021-47376 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 May 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-2021-47376 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-2021-47376/ (Markdown: https://insights.sbomify.com/CVE-2021-47376/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47376
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47376
- OSV: https://osv.dev/vulnerability/CVE-2021-47376

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47376/
Summaries are generated and may contain mistakes; the official description above is the record.