CVE-2025-21854 sockmap, vsock: For connectible sockets allow only connected
A null pointer dereference in the Linux kernel vsock subsystem allows local attackers to cause a system crash via specific socket states.
- 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-2025-21854?
CVE-2025-21854 is a medium-severity vulnerability in Linux kernel, published on 12 Mar 2025. 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:
sockmap, vsock: For connectible sockets allow only connected
sockmap expects all vsocks to have a transport assigned, which is expressed in vsock_proto::psock_update_sk_prot(). However, there is an edge case where an unconnected (connectible) socket may lose its previously assigned transport. This is handled with a NULL check in the vsock/BPF recv path.
Another design detail is that listening vsocks are not supposed to have any transport assigned at all. Which implies they are not supported by the sockmap. But this is complicated by the fact that a socket, before switching to TCP_LISTEN, may have had some transport assigned during a failed connect() attempt. Hence, we may end up with a listening vsock in a sockmap, which blows up quickly:
KASAN: null-ptr-deref in range [0x0000000000000120-0x0000000000000127] CPU: 7 UID: 0 PID: 56 Comm: kworker/7:0 Not tainted 6.14.0-rc1+ Workqueue: vsock-loopback vsock_loopback_work RIP: 0010:vsock_read_skb+0x4b/0x90 Call Trace: sk_psock_verdict_data_ready+0xa4/0x2e0 virtio_transport_recv_pkt+0x1ca8/0x2acc vsock_loopback_work+0x27d/0x3f0 process_one_work+0x846/0x1420 worker_thread+0x5b3/0xf80 kthread+0x35a/0x700 ret_from_fork+0x2d/0x70 ret_from_fork_asm+0x1a/0x30
For connectible sockets, instead of relying solely on the state of vsk->transport, tell sockmap to only allow those representing established connections. This aligns with the behaviour for AF_INET and AF_UNIX.
Weakness: CWE-476
Which versions are affected by CVE-2025-21854?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21854?
Apply the vendor's patch.
Is CVE-2025-21854 being exploited?
There is no known exploitation of CVE-2025-21854 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-58508, BELL-CVE-2025-21854, DEBIAN-CVE-2025-21854, GHSA-vwm2-mqfj-r5v5, ROOT-OS-UBUNTU-2404-CVE-2025-21854, UBUNTU-CVE-2025-21854.