# CVE-2024-43887: net/tcp: Disable TCP-AO static key after RCU grace period

> A race condition in Linux kernel TCP-AO static key handling can cause a kernel bug and system crash during socket destruction.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/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:** 26 Aug 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2024-43887, DEBIAN-CVE-2024-43887, GHSA-7566-65rj-g85x, UBUNTU-CVE-2024-43887

## What is CVE-2024-43887?

CVE-2024-43887 is a medium-severity vulnerability in Linux kernel, published on 26 Aug 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:

net/tcp: Disable TCP-AO static key after RCU grace period

The lifetime of TCP-AO static_key is the same as the last
tcp_ao_info. On the socket destruction tcp_ao_info ceases to be
with RCU grace period, while tcp-ao static branch is currently deferred
destructed. The static key definition is
: DEFINE_STATIC_KEY_DEFERRED_FALSE(tcp_ao_needed, HZ);

which means that if RCU grace period is delayed by more than a second
and tcp_ao_needed is in the process of disablement, other CPUs may
yet see tcp_ao_info which atent dead, but soon-to-be.
And that breaks the assumption of static_key_fast_inc_not_disabled().

See the comment near the definition:
> * The caller must make sure that the static key can't get disabled while
> * in this function. It doesn't patch jump labels, only adds a user to
> * an already enabled static key.

Originally it was introduced in commit eb8c507296f6 ("jump_label:
Prevent key->enabled int overflow"), which is needed for the atomic
contexts, one of which would be the creation of a full socket from a
request socket. In that atomic context, it's known by the presence
of the key (md5/ao) that the static branch is already enabled.
So, the ref counter for that static branch is just incremented
instead of holding the proper mutex.
static_key_fast_inc_not_disabled() is just a helper for such usage
case. But it must not be used if the static branch could get disabled
in parallel as it's not protected by jump_label_mutex and as a result,
races with jump_label_update() implementation details.

Happened on netdev test-bot[1], so not a theoretical issue:

[] jump_label: Fatal kernel bug, unexpected op at tcp_inbound_hash+0x1a7/0x870 [ffffffffa8c4e9b7] (eb 50 0f 1f 44 != 66 90 0f 1f 00)) size:2 type:1
[] ------------[ cut here ]------------
[] kernel BUG at arch/x86/kernel/jump_label.c:73!
[] Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
[] CPU: 3 PID: 243 Comm: kworker/3:3 Not tainted 6.10.0-virtme #1
[] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[] Workqueue: events jump_label_update_timeout
[] RIP: 0010:__jump_label_patch+0x2f6/0x350
...
[] Call Trace:
[]  <TASK>
[]  arch_jump_label_transform_queue+0x6c/0x110
[]  __jump_label_update+0xef/0x350
[]  __static_key_slow_dec_cpuslocked.part.0+0x3c/0x60
[]  jump_label_update_timeout+0x2c/0x40
[]  process_one_work+0xe3b/0x1670
[]  worker_thread+0x587/0xce0
[]  kthread+0x28a/0x350
[]  ret_from_fork+0x31/0x70
[]  ret_from_fork_asm+0x1a/0x30
[]  </TASK>
[] Modules linked in: veth
[] ---[ end trace 0000000000000000 ]---
[] RIP: 0010:__jump_label_patch+0x2f6/0x350

[1]: https://netdev-3.bots.linux.dev/vmksft-tcp-ao-dbg/results/696681/5-connect-deny-ipv6/stderr

## Which versions are affected by CVE-2024-43887?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-43887?

Apply the vendor's patch.

## Is CVE-2024-43887 being exploited?

There is no known exploitation of CVE-2024-43887 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-2024-43887 and fix it if it is affected.

What it is: CVE-2024-43887 is a medium-severity vulnerability in Linux kernel, published on 26 Aug 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-2024-43887 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-2024-43887/ (Markdown: https://insights.sbomify.com/CVE-2024-43887/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-43887
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-43887
- OSV: https://osv.dev/vulnerability/CVE-2024-43887

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-43887/
Summaries are generated and may contain mistakes; the official description above is the record.