CVE-2026-64137 smb: client: require net admin for CIFS SWN netlink
Unprivileged local processes can access sensitive CIFS witness data and send notifications due to missing capability checks in the Linux kernel SMB client.
- 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-2026-64137?
CVE-2026-64137 is a high-severity missing authorization vulnerability in Linux kernel, published on 19 Jul 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:
smb: client: require net admin for CIFS SWN netlink
CIFS_GENL_CMD_SWN_NOTIFY is the userspace witness-notify command. The intended sender is the cifs.witness helper, but the generic-netlink operation currently has no capability flag, so any local process can send RESOURCE_CHANGE or CLIENT_MOVE notifications to the in-kernel witness handler.
The same family exposes CIFS_GENL_MCGRP_SWN without multicast-group capability flags. Register messages sent to that group include the witness registration id and, for NTLM-authenticated mounts, the username, domain, and password attributes copied from the CIFS session. An unprivileged local process should not be able to join that group and receive those messages.
Require CAP_NET_ADMIN for incoming SWN_NOTIFY commands with GENL_ADMIN_PERM, and require CAP_NET_ADMIN over the network namespace for joining the SWN multicast group with GENL_MCAST_CAP_NET_ADMIN. The cifs.witness service runs with the privileges needed for both operations.
Which versions are affected by CVE-2026-64137?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-64137?
Apply the vendor's patch.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-64137 being exploited?
There is no known exploitation of CVE-2026-64137 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-64137, DEBIAN-CVE-2026-64137, GHSA-5vrr-7h3c-f6hv, ROOT-OS-UBUNTU-2204-CVE-2026-64137, UBUNTU-CVE-2026-64137.