# CVE-2026-74586: sctp: clear new_transport when removing a peer

> A use-after-free in the Linux kernel SCTP implementation allows remote attackers to cause a denial of service or potentially execute code via crafted ASCONF chunks.

- **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:** 22 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-97374, BELL-CVE-2026-74586, DEBIAN-CVE-2026-74586, GHSA-p4vf-g6h3-f897, UBUNTU-CVE-2026-74586

## What is CVE-2026-74586?

CVE-2026-74586 is a critical use after free vulnerability in Linux, published on 22 Aug 2026. 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: clear new_transport when removing a peer

sctp_process_asconf_param() stores a newly added peer transport in
asoc->new_transport. After all parameters in the ASCONF chunk have been
processed, sctp_sf_do_asconf() uses this pointer to send a HEARTBEAT to the
new transport.

An authenticated ASCONF from a remote SCTP peer can add a transport and
remove it again with a wildcard DEL-IP parameter in the same chunk. The
wildcard deletion preserves the transport on which the ASCONF arrived, but
removes the newly added transport through
sctp_assoc_del_nonprimary_peers(). The removal does not clear
asoc->new_transport, leaving it pointing to the removed transport.

sctp_sf_do_asconf() then creates a HEARTBEAT whose chunk->transport points
to the removed transport without holding a transport reference. During
local address replacement, src_out_of_asoc_ok keeps this HEARTBEAT on
control_chunk_list. After the transport is freed by RCU, a successful
ASCONF_ACK for the replacement address releases the queued HEARTBEAT and
sctp_outq_select_transport() reads the freed transport's state.

The issue was found during a static audit of SCTP objects. With an
authenticated peer, the reproducer triggered the same KASAN report in 2
of 2 unpatched runs on a KASAN-enabled netdev/main kernel:

  BUG: KASAN: slab-use-after-free in sctp_outq_select_transport
  Read of size 4 at addr ffff88800b9bd95c by task python3/197

  Call Trace:
   sctp_outq_select_transport+0x549/0x8b0 [sctp]
   sctp_outq_flush+0x306/0x2c60 [sctp]
   sctp_transport_immediate_rtx+0xaf/0x260 [sctp]
   sctp_process_asconf_ack+0xa48/0xf70 [sctp]

  Allocated by task 197:
   sctp_transport_new+0x68/0x650 [sctp]
   sctp_assoc_add_peer+0x258/0x12a0 [sctp]
   sctp_process_asconf+0x5e9/0x1090 [sctp]

  Last potentially related work creation:
   __call_rcu_common.constprop.0+0x77/0xb70
   sctp_assoc_del_nonprimary_peers+0x7c/0xd0 [sctp]
   sctp_process_asconf+0xd9c/0x1090 [sctp]

The first invalid access was a four-byte read of transport->state at
net/sctp/outqueue.c:833. The same reproducer completed the full
authenticated ASCONF and local-address replacement sequence with this
change without a KASAN report or oops.

Clear new_transport when its peer is removed, before it can be used to
create the HEARTBEAT.

## Which versions are affected by CVE-2026-74586?


## How do I fix CVE-2026-74586?

Apply the vendor's patch.

## Is CVE-2026-74586 being exploited?

There is no known exploitation of CVE-2026-74586 in the wild and no public exploit code.

Public exploit code:

- https://github.com/TarPeg007/CVE-2026-74586 (github_poc): https://github.com/TarPeg007/CVE-2026-74586

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74586 and fix it if it is affected.

What it is: CVE-2026-74586 is a critical use after free vulnerability in Linux, published on 22 Aug 2026. 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-2026-74586 in the wild and no public exploit code.

Affected product: Linux. 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-2026-74586/ (Markdown: https://insights.sbomify.com/CVE-2026-74586/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74586
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74586
- OSV: https://osv.dev/vulnerability/CVE-2026-74586

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74586/
Summaries are generated and may contain mistakes; the official description above is the record.