# CVE-2026-74587: sctp: fix use-after-free of cached ASCONF chunk

> A use-after-free in the Linux kernel SCTP implementation allows attackers to trigger memory corruption, potentially leading to code execution or system crashes.

- **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-97136, BELL-CVE-2026-74587, DEBIAN-CVE-2026-74587, GHSA-5vmc-fx99-r54r, UBUNTU-CVE-2026-74587

## What is CVE-2026-74587?

CVE-2026-74587 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: fix use-after-free of cached ASCONF chunk

addip_last_asconf caches the outstanding outbound ASCONF chunk. The normal
ASCONF-ACK completion path releases the chunk and clears the pointer.

However, sctp_asconf_queue_teardown() releases the cached chunk without
clearing addip_last_asconf. During peer restart handling,
sctp_sf_do_dupcook_a() queues SCTP_CMD_PURGE_ASCONF_QUEUE, which invokes
sctp_asconf_queue_teardown() while the association remains alive and leaves
the pointer dangling.

A delayed authenticated ASCONF-ACK can then reach sctp_sf_do_asconf_ack(),
which accesses the stale chunk and passes it to sctp_process_asconf_ack(),
causing a use-after-free and a second release.

Clearing the pointer exposes a race with T4 expiry. Peer restart handling
queues the timer stop before the purge, but SCTP_CMD_TIMER_STOP uses
timer_delete(), which does not wait for a callback already running on
another CPU. Such a callback can reach sctp_sf_t4_timer_expire() after
the purge and dereference NULL.

Clear addip_last_asconf after releasing the cached chunk, and make
sctp_sf_t4_timer_expire() consume a stale T4 expiry if no outstanding
ASCONF remains.

## Which versions are affected by CVE-2026-74587?


## How do I fix CVE-2026-74587?

Apply the vendor's patch.

## Is CVE-2026-74587 being exploited?

There is no known exploitation of CVE-2026-74587 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74587 and fix it if it is affected.

What it is: CVE-2026-74587 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-2026-74587 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-2026-74587/ (Markdown: https://insights.sbomify.com/CVE-2026-74587/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74587
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74587
- OSV: https://osv.dev/vulnerability/CVE-2026-74587

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74587/
Summaries are generated and may contain mistakes; the official description above is the record.