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CVE-2026-64137
smb: client: require net admin for CIFS SWN netlink
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem fs/smb. Debian urgency: not yet assigned.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-64137 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixed | 6.1.176-1 | Update the kernel and reboot. Fixed in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/smb/client/netlink.c
- What this is
- COMMON INTERNET FILE SYSTEM CLIENT (CIFS and SMB3)MAINTAINERS section matched on fs/smb/client/ · linux-cifs@vger.kernel.org · Supported
- Kernel module
- none to look for. The file would have gone into cifs, and Debian does not compile it into that module, so finding cifs in lsmod would say nothing about this CVE.
Check it on the machine
grep -wE 'CONFIG_CIFS|CONFIG_CIFS_SWN_UPCALL|CONFIG_SMBFS' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian does not build this code. In 4 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sidn
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_CIFS, CONFIG_CIFS_SWN_UPCALL, CONFIG_SMBFS
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-07-19 (3 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/smb
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.11 | 5.15.210 | 9cf7eb891934 |
| 5.11 | 6.1.176 | 9919021a3b79 |
| 5.11 | 6.6.143 | 969bc6370334 |
| 5.11 | 6.12.92 | a3238b09c58f |
| 5.11 | 6.18.34 | a8d17d22db59 |
| 5.11 | 7.0.11 | c2397b93fbb6 |
| 5.11 | 7.1 | d1ebfce2c1d1 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- Exploitation requires local access via generic-netlink syscalls (socket/bind/sendmsg/setsockopt on NETLINK_GENERIC), not remote SMB or network packet handling.
- AC:LAttack complexity, low
- An unprivileged attacker can reliably join the SWN multicast group and send crafted SWN_NOTIFY commands; registration IDs are exposed in multicast register messages, with no races or uncontrollable conditions.
- PR:LPrivileges required, low
- Before the fix, no capability checks guarded SWN_NOTIFY or multicast group membership, so any unprivileged local user could exploit without CAP_NET_ADMIN or user-namespace tricks.
- UI:NUser interaction, none
- Exploitation is passive (multicast subscription) or active (netlink injection) and does not require any victim action at attack time beyond pre-existing witness-enabled CIFS mounts.
- S:UScope, unchanged
- Impact is confined to the local kernel/CIFS client security domain (credential theft and connection manipulation); it does not cross VM, container, or IOMMU boundaries.
- C:HConfidentiality impact, high
- Multicast register messages disclose NTLM username, domain, and plaintext password from active CIFS witness sessions to any local subscriber.
- I:HIntegrity impact, high
- Forged CLIENT_MOVE notifications redirect SMB reconnects to attacker-controlled endpoints, compromising connection integrity and enabling MITM against mounted cluster shares.
- A:HAvailability impact, high
- Forged RESOURCE_CHANGE notifications force CIFS reconnect cycles on all channels, enabling reliable denial-of-service against witness-enabled mounts.