CVE-2026-97985 af_unix: Update last skb marker in manage_oob().
A local attacker can cause a CPU busy-wait denial of service in the Linux kernel by triggering a specific out-of-band socket condition during a blocking peek operation.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-97985?
CVE-2026-97985 is a denial of service vulnerability in Linux, published on 25 Sep 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: Update last skb marker in manage_oob().
Fahad Alharbi reported that blocking recv(MSG_PEEK) could hog CPU due to OOB skb.
In the following cases, manage_oob() skips OOB skb(s) and returns NULL for the last recv(MSG_PEEK):
socketpair(AF_UNIX, SOCK_STREAM, 0, sk);
1) skb -> OOB skb -> NULL send(sk[0], "ab", 2, MSG_OOB); recv(sk[1], buf, 0, MSG_PEEK);
2) skb -> consumed OOB skb -> NULL send(sk[0], "ab", 2, MSG_OOB); recv(sk[1], buf, 1, MSG_OOB); recv(sk[1], buf, 0, MSG_PEEK);
3) consumed OOB skb -> OOB skb -> NULL send(sk[0], "a", 1, MSG_OOB); recv(sk[1], buf, 0, MSG_OOB); send(sk[0], "b", 1, MSG_OOB); recv(sk[1], buf, 1, MSG_PEEK);
Then, @copied is 0 in unix_stream_read_generic() (zero-length buffer, or non-OOB skb is not yet consumed), and unix_stream_data_wait() is called.
However, it returns immediately because @last is not updated in unix_stream_read_generic(), and the thread busy-waits for a new skb.
Let's update @last in manage_oob().
For MSG_PEEK, @last is updated with the skipped OOB, and for the non-peek case, @last matches the returned value (when !copied) because OOB is unlinked.
Note that manage_oob() is inlined and no stack canary is added.
Which versions are affected by CVE-2026-97985?
How do I fix CVE-2026-97985?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-97985 being exploited?
There is no known exploitation of CVE-2026-97985 in the wild and no public exploit code.
Sources
Also known as AZL-104352, BELL-CVE-2026-97985, DEBIAN-CVE-2026-97985, GHSA-cq66-2f6w-rhg5, UBUNTU-CVE-2026-97985.