# CVE-2025-21683: bpf: Fix bpf_sk_select_reuseport() memory leak

> A memory leak in the Linux kernel's BPF subsystem allows local attackers to exhaust system memory, leading to 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:** 31 Jan 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-56268, AZL-56333, BELL-CVE-2025-21683, DEBIAN-CVE-2025-21683, GHSA-fjfj-r96f-8hqw, UBUNTU-CVE-2025-21683

## What is CVE-2025-21683?

CVE-2025-21683 is a medium-severity memory corruption vulnerability in Linux kernel, published on 31 Jan 2025. 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: Fix bpf_sk_select_reuseport() memory leak

As pointed out in the original comment, lookup in sockmap can return a TCP
ESTABLISHED socket. Such TCP socket may have had SO_ATTACH_REUSEPORT_EBPF
set before it was ESTABLISHED. In other words, a non-NULL sk_reuseport_cb
does not imply a non-refcounted socket.

Drop sk's reference in both error paths.

unreferenced object 0xffff888101911800 (size 2048):
  comm "test_progs", pid 44109, jiffies 4297131437
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    80 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace (crc 9336483b):
    __kmalloc_noprof+0x3bf/0x560
    __reuseport_alloc+0x1d/0x40
    reuseport_alloc+0xca/0x150
    reuseport_attach_prog+0x87/0x140
    sk_reuseport_attach_bpf+0xc8/0x100
    sk_setsockopt+0x1181/0x1990
    do_sock_setsockopt+0x12b/0x160
    __sys_setsockopt+0x7b/0xc0
    __x64_sys_setsockopt+0x1b/0x30
    do_syscall_64+0x93/0x180
    entry_SYSCALL_64_after_hwframe+0x76/0x7e

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2025-21683?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21683?

Apply the vendor's patch.

## Is CVE-2025-21683 being exploited?

There is no known exploitation of CVE-2025-21683 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-2025-21683 and fix it if it is affected.

What it is: CVE-2025-21683 is a medium-severity memory corruption vulnerability in Linux kernel, published on 31 Jan 2025. 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-2025-21683 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-2025-21683/ (Markdown: https://insights.sbomify.com/CVE-2025-21683/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21683
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21683
- OSV: https://osv.dev/vulnerability/CVE-2025-21683

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21683/
Summaries are generated and may contain mistakes; the official description above is the record.