CVE-2026-64137: smb: client: require net admin for CIFS SWN netlink
In the Linux kernel, the following vulnerability has been resolved:
smb: client: require net admin for CIFS SWN netlink
CIFSGENLCMDSWNNOTIFY 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 RESOURCECHANGE or CLIENTMOVE notifications to the in-kernel witness handler.
The same family exposes CIFSGENLMCGRPSWN 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 CAPNETADMIN for incoming SWNNOTIFY commands with GENLADMINPERM, and require CAPNETADMIN over the network namespace for joining the SWN multicast group with GENLMCASTCAPNETADMIN. The cifs.witness service runs with the privileges needed for both operations.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Configuration
Update/enable the kernel change so incoming SWN_NOTIFY (CIFS_GENL_CMD_SWN_NOTIFY) commands require CAP_NET_ADMIN over the network namespace, preventing unprivileged local processes from registering/sending witness-notify messages.
Linux kernel CIFS witness generic-netlink (CIFS_GENL_CMD_SWN_NOTIFY / SWN_NOTIFY) Require CAP_NET_ADMIN for incoming SWN_NOTIFY commands = CAP_NET_ADMIN required (network namespace) - Configuration
Update/enable the kernel behavior so joining the SWN multicast group requires GENL_MCAST_CAP_NET_ADMIN, ensuring local processes cannot join and receive witness Register messages.
Linux kernel CIFS witness generic-netlink multicast group (SWN multicast group) Multicast group join capability (GENL_MCAST_CAP_NET_ADMIN) = GENL_MCAST_CAP_NET_ADMIN
Event History
Frequently Asked Questions
What is the severity of CVE-2026-64137?
The severity of CVE-2026-64137 is rated as high with a CVSS score of 7.8.
What does CVE-2026-64137 affect?
CVE-2026-64137 affects the Linux kernel, specifically related to the SMB client and CIFS netlink operations.
How do I fix CVE-2026-64137?
To fix CVE-2026-64137, it's recommended to update the Linux kernel to the latest version where this vulnerability has been resolved.
What type of vulnerability is CVE-2026-64137?
CVE-2026-64137 is a privilege escalation vulnerability that allows unauthorized capabilities for specific netlink operations.
Can CVE-2026-64137 be exploited remotely?
Yes, CVE-2026-64137 can be potentially exploited remotely if the affected environment allows SMB operations without proper access controls.