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CVE-2026-64386
smb: client: fix query_info() replay double-free
Published 2026-07-25 (3 months ago) by the Linux kernel CNA. Subsystem fs/smb. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-64386 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixed | 6.12.96-1 | Update the kernel and reboot. Fixed in 6.12.96-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
A response-bearing attempt can return a replayable error and free its response buffer. If SMB2_query_info_init() fails before the next send, cleanup retains the previous buffer type and frees that response again. Reset response bookkeeping before each attempt to prevent the stale free.
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/smb2pdu.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, sid, bookworm · linux-6.12m
- 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
- 2026-07-25 (3 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.46%, higher than 38.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.6.32 | 6.6.145 | 100fb7c455fa |
| 6.8 | 6.12.96 | 3c81dda84799 |
| 6.8 | 6.18.39 | f1add4acb656 |
| 6.8 | 7.1.4 | 89234773e834 |
| 6.8 | 7.2 | 2a88561d66eb |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | 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
- A malicious or compromised SMB2/3 server can remotely return a response-bearing replayable error and manipulate the subsequent connection state, reaching the vulnerable client over TCP.
- AC:LAttack complexity, low
- The server controls the error response, disconnect, and reconnection sequence and can repeat it until the stale free occurs. Replay-enabled hard or retrans-configured SMB mounts are a reasonable deployment.
- PR:NPrivileges required, none
- The malicious SMB peer needs no privileges or credentials on the client; SMB session setup authenticates the client to the server, not the attacker to the victim kernel.
- UI:NUser interaction, none
- Once the share is mounted, ordinary or automated file and metadata operations issue query-info requests, and exploitation requires no human action during the crafted response and reconnect sequence.
- S:UScope, unchanged
- The corruption and resulting impacts occur within the same Linux kernel security authority, without crossing a VM, sandbox, or IOMMU boundary.
- C:HConfidentiality impact, high
- The double-free corrupts SMB response-buffer slab and mempool state, enabling aliased or use-after-free buffers that can be leveraged to expose kernel memory.
- I:HIntegrity impact, high
- Allocator freelist corruption and reuse of one buffer by concurrent SMB operations can provide attacker-controlled modification of live kernel memory and support control-flow hijacking.
- A:HAvailability impact, high
- The repeated free can immediately cause allocator corruption, a BUG, kernel oops, or panic, and the malicious server can trigger the sequence repeatedly.