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CVE-2026-23226
ksmbd: add chann_lock to protect ksmbd_chann_list xarray
Published 2026-02-18 (8 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-2026-23226 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 | fixedDSA-6238-1 · 2026-04-30 · text | 6.12.85-1 | Update the kernel and reboot. DSA-6238-1 shipped the fix on 2026-04-30, in 6.12.85-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.18.12-1 | Update the kernel and reboot. Fixed in 6.18.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.18.12-1 | Update the kernel and reboot. Fixed in 6.18.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
ksmbd_chann_list xarray lacks synchronization, allowing use-after-free in multi-channel sessions (between lookup_chann_list() and ksmbd_chann_del). Adds rw_semaphore chann_lock to struct ksmbd_session and protects all xa_load/xa_store/xa_erase accesses.
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/server/mgmt/user_session.c
fs/smb/server/mgmt/user_session.h
fs/smb/server/smb2pdu.c
- What this is
- KERNEL SMB3 SERVER (KSMBD)MAINTAINERS section matched on fs/smb/server/ · linux-cifs@vger.kernel.org · Maintained
- Kernel module
- ksmbd
Check it on the machine
grep -wE 'CONFIG_SMBFS|CONFIG_SMB_SERVER' /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 ksmbdPrints 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_SMBFS, CONFIG_SMB_SERVER
- 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
- 2026-02-18 (8 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.46%, higher than 38.1% 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 |
|---|---|---|
| 6.3 | 6.12.77 | 4c2ca3160852 |
| 6.3 | 6.18.11 | e4a8a96a93d0 |
| 6.3 | 6.19.1 | 36ef605c0395 |
| 6.3 | 7.0 | 4f3a06cc5797 |
| 5.15.145 | 0 | 0 |
| 6.1.29 | 0 | 0 |
| 6.2.16 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DSA-6238-1 | 2026-04-30 | trixie 6.12.85-1 | tracker |
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
- ksmbd is the in-kernel SMB server listening on TCP port 445, directly reachable over the network.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by establishing multiple SMB connections (multi-channel session) and timing a disconnect on one while the other accesses the channel list. The attacker creates and controls the race condition.
- PR:LPrivileges required, low
- The channel list is populated during ntlm_authenticate() or krb5_authenticate(), requiring valid SMB credentials to establish a session before the race can be triggered. This is post-authentication.
- UI:NUser interaction, none
- No user interaction is needed; the attacker initiates and controls all SMB connections and their timing.
- S:UScope, unchanged
- The vulnerability and its impact remain within the kernel security authority; no security boundary (e.g., VM, sandbox) is crossed.
- C:HConfidentiality impact, high
- Use-after-free on struct channel allows reading freed memory that may be reallocated with attacker-controlled content, enabling arbitrary kernel memory disclosure including signing keys.
- I:HIntegrity impact, high
- Use-after-free enables heap spraying to replace the freed channel struct, allowing attacker-controlled data to be used as signing keys or function pointers, leading to arbitrary code execution.
- A:HAvailability impact, high
- Use-after-free reliably causes kernel crashes (oops/panic) when the freed channel pointer is dereferenced, causing denial of service.