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CVE-2026-43239
smb: client: prevent races in ->query_interfaces()
Published 2026-05-06 (5 months ago) by the Linux kernel CNA. Subsystem fs/smb. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-43239 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixed | 6.12.85-1 | Update the kernel and reboot. Fixed in 6.12.85-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.19.6-1 | Update the kernel and reboot. Fixed in 6.19.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.19.6-1 | Update the kernel and reboot. Fixed in 6.19.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
It was possible for two query interface works to be concurrently trying to update the interfaces. Prevent this by checking and updating iface_last_update under iface_lock.
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/smb2ops.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
- cifs
Check it on the machine
grep -wE 'CONFIG_CIFS|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.
lsmod | grep -w cifsPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_CIFS, 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
- 2026-05-06 (5 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.35%, higher than 27.5% 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 |
|---|---|---|
| 5.19 | 6.6.128 | 93e8e3ee165a |
| 5.19 | 6.12.75 | ab6564f416a6 |
| 5.19 | 6.18.16 | 6287eefaf21e |
| 5.19 | 6.19.6 | 76cc4faba034 |
| 5.19 | 7.0 | c3c06e42e152 |
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:NAttack vector, network
- The vulnerable SMB client code processes FSCTL_QUERY_NETWORK_INTERFACE_INFO responses supplied by a remote SMB server over the network.
- AC:LAttack complexity, low
- The required SMB3/multichannel capability and response timing can be controlled by a malicious server, and concurrent interface queries can be induced through normal mounted-session refresh/reconnect behavior.
- PR:NPrivileges required, none
- The attacker needs no privileges on the victim system; a malicious or compromised SMB server can supply the responses once the client connects.
- UI:RUser interaction, required
- Exploitation requires the victim system or user to mount/connect to the SMB share, which is user interaction under the provided guidance.
- S:UScope, unchanged
- The impact is within the client kernel that contains the vulnerable SMB client component, without crossing a separate security authority such as a VM boundary.
- C:HConfidentiality impact, high
- The race can corrupt the kernel-maintained cifs_server_iface linked list/refcount state, and kernel heap/list corruption is defensibly treated as potentially exposing arbitrary kernel memory.
- I:HIntegrity impact, high
- The same kernel list corruption can plausibly be leveraged beyond a simple fault into kernel memory corruption or code execution, so integrity impact is high under the required higher-severity rule.
- A:HAvailability impact, high
- Even without full exploitation, the race can corrupt interface-list state and trigger kernel oops/panic or hang in the SMB client path.