CVE-2026-80521 af_unix: Unlink scc_entry in unix_del_edge().

What is CVE-2026-80521?

CVE-2026-80521 is a high-severity use after free vulnerability in Linux, published on 26 Aug 2026. 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:

af_unix: Unlink scc_entry in unix_del_edge().

Kyle Zeng reported that GC could free a dead SCC partially.

The scenario is as follows:

1) Create two SCCs:

X -. A <-> B ^--'

2) Run the following concurrently:

2-1) send() sk-B to sk-B from sk-X 2-2) close() both A and B

At 2-1), there is a small window where unix_add_edges() publishes a new edge (B <-> B) to GC but its skb is not queued by skb_queue_tail().

If 2-2) completes before skb_queue_tail() and GC is triggered, it judges A <-> B as dead, but B is not freed because GC cannot collect the not-yet-queued skb holding the B <-> B edge.

X -. A <-> B -. This edge is visible ^--' ^..' but skb is not

This itself is not a problem since the next GC run will judge B as dead as well and free it finally.

X -. A <.> B -. ^--' ^--'

However, X's SCC forces the next GC to call unix_walk_scc_fast(), and it iterates over A through B's scc_entry.

Let's unlink scc_entry before freeing the vertex in unix_del_edge().

Which versions are affected by CVE-2026-80521?

How do I fix CVE-2026-80521?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2026-80521 being exploited?

There is no known exploitation of CVE-2026-80521 in the wild and no public exploit code.

Public exploit code: 2 proofs of concept on GitHub.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-97814, BELL-CVE-2026-80521, DEBIAN-CVE-2026-80521, GHSA-g8mr-r59r-2xmq, UBUNTU-CVE-2026-80521.