# CVE-2026-80849: net/tcp-ao: fix use-after-free of current_key on reconnect to another peer

> A use-after-free in the Linux kernel TCP-AO implementation allows remote attackers to cause denial of service or execute arbitrary code via crafted network packets.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-80849, DEBIAN-CVE-2026-80849, GHSA-p98r-rj2f-59m7, UBUNTU-CVE-2026-80849

## What is CVE-2026-80849?

CVE-2026-80849 is an use after free vulnerability in Linux, published on 4 Sep 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:

net/tcp-ao: fix use-after-free of current_key on reconnect to another peer

tcp_inbound_ao_hash() is called before bh_lock_sock_nested() is taken,
with only rcu_read_lock() held. On the fast path for established
sockets, if the rnext_keyid sent by the peer differs from
current_key->sndid, the key the peer asked for is looked up and stored
in current_key. The lookup is inside the RCU read side, but current_key
outlives it.

When the socket is disconnected and connect() is called again for
another peer, tcp_ao_connect_init() unlinks every key that does not
match the new peer and frees it with call_rcu(). If current_key points
at such a key, it is cleared to NULL.

The fast path reads sk_state only once on entry, so a softirq that got
into it while the socket was still established can update current_key
after that loop has already run. The update is inside the RCU read side,
so it comes before the call_rcu() callback, and once the callback frees
the key, current_key is left pointing at freed memory.

The next transmission picks that pointer up in tcp_get_current_key().
tcp_ao_transmit_skb() then reads the traffic key from the freed object,
which is the use-after-free.

Wait for one grace period before unlinking, and only if a key is going
to be removed. By the time tcp_connect() runs the socket is already in
TCP_SYN_SENT, and TCP_AO_ESTABLISHED does not contain TCPF_SYN_SENT, so
a softirq entering after the wait cannot reach the fast path, and the
ones already in it have finished. The existing NULL handling in the loop
is then enough.

## Which versions are affected by CVE-2026-80849?


## How do I fix CVE-2026-80849?

Apply the vendor's patch.

## Is CVE-2026-80849 being exploited?

There is no known exploitation of CVE-2026-80849 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80849 and fix it if it is affected.

What it is: CVE-2026-80849 is an use after free vulnerability in Linux, published on 4 Sep 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-2026-80849 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-2026-80849/ (Markdown: https://insights.sbomify.com/CVE-2026-80849/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80849
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80849
- OSV: https://osv.dev/vulnerability/CVE-2026-80849

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80849/
Summaries are generated and may contain mistakes; the official description above is the record.