CVE-2026-23057 vsock/virtio: Coalesce only linear skb
A flaw in Linux kernel vsock/virtio allows uninitialized kernel memory disclosure when coalescing non-linear skbs in loopback transport.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23057?
CVE-2026-23057 is a vulnerability in Linux, published on 4 Feb 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:
vsock/virtio: Coalesce only linear skb
vsock/virtio common tries to coalesce buffers in rx queue: if a linear skb (with a spare tail room) is followed by a small skb (length limited by GOOD_COPY_LEN = 128), an attempt is made to join them.
Since the introduction of MSG_ZEROCOPY support, assumption that a small skb will always be linear is incorrect. In the zerocopy case, data is lost and the linear skb is appended with uninitialized kernel memory.
Of all 3 supported virtio-based transports, only loopback-transport is affected. G2H virtio-transport rx queue operates on explicitly linear skbs; see virtio_vsock_alloc_linear_skb() in virtio_vsock_rx_fill(). H2G vhost-transport may allocate non-linear skbs, but only for sizes that are not considered for coalescence; see PAGE_ALLOC_COSTLY_ORDER in virtio_vsock_alloc_skb().
Ensure only linear skbs are coalesced. Note that skb_tailroom(last_skb) > 0 guarantees last_skb is linear.
Which versions are affected by CVE-2026-23057?
How do I fix CVE-2026-23057?
Apply the vendor's patch.
Is CVE-2026-23057 being exploited?
There is no known exploitation of CVE-2026-23057 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-23057, DEBIAN-CVE-2026-23057, GHSA-2725-mxxg-w826, ROOT-OS-DEBIAN-13-CVE-2026-23057, ROOT-OS-UBUNTU-2404-CVE-2026-23057, UBUNTU-CVE-2026-23057.