# CVE-2021-46999: sctp: do asoc update earlier in sctp_sf_do_dupcook_a

> A use-after-free vulnerability in the Linux kernel SCTP implementation allows attackers to cause a system crash via a general protection fault.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Feb 2024
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2021-46999, GHSA-c4xm-6jcf-xfq6, UBUNTU-CVE-2021-46999

## What is CVE-2021-46999?

CVE-2021-46999 is a critical use after free vulnerability in Linux kernel, published on 28 Feb 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

sctp: do asoc update earlier in sctp_sf_do_dupcook_a

There's a panic that occurs in a few of envs, the call trace is as below:

  [] general protection fault, ... 0x29acd70f1000a: 0000 [#1] SMP PTI
  [] RIP: 0010:sctp_ulpevent_notify_peer_addr_change+0x4b/0x1fa [sctp]
  []  sctp_assoc_control_transport+0x1b9/0x210 [sctp]
  []  sctp_do_8_2_transport_strike.isra.16+0x15c/0x220 [sctp]
  []  sctp_cmd_interpreter.isra.21+0x1231/0x1a10 [sctp]
  []  sctp_do_sm+0xc3/0x2a0 [sctp]
  []  sctp_generate_timeout_event+0x81/0xf0 [sctp]

This is caused by a transport use-after-free issue. When processing a
duplicate COOKIE-ECHO chunk in sctp_sf_do_dupcook_a(), both COOKIE-ACK
and SHUTDOWN chunks are allocated with the transort from the new asoc.
However, later in the sideeffect machine, the old asoc is used to send
them out and old asoc's shutdown_last_sent_to is set to the transport
that SHUTDOWN chunk attached to in sctp_cmd_setup_t2(), which actually
belongs to the new asoc. After the new_asoc is freed and the old asoc
T2 timeout, the old asoc's shutdown_last_sent_to that is already freed
would be accessed in sctp_sf_t2_timer_expire().

Thanks Alexander and Jere for helping dig into this issue.

To fix it, this patch is to do the asoc update first, then allocate
the COOKIE-ACK and SHUTDOWN chunks with the 'updated' old asoc. This
would make more sense, as a chunk from an asoc shouldn't be sent out
with another asoc. We had fixed quite a few issues caused by this.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-46999?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-46999?

Apply the vendor's patch.

## Is CVE-2021-46999 being exploited?

There is no known exploitation of CVE-2021-46999 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-2021-46999 and fix it if it is affected.

What it is: CVE-2021-46999 is a critical use after free vulnerability in Linux kernel, published on 28 Feb 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-46999 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-2021-46999/ (Markdown: https://insights.sbomify.com/CVE-2021-46999/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-46999
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-46999
- OSV: https://osv.dev/vulnerability/CVE-2021-46999

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-46999/
Summaries are generated and may contain mistakes; the official description above is the record.