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CVE-2026-72310
smb: client: fix overflow in passthrough ioctl bounds check
Published 2026-08-15 (2 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-2026-72310 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 | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
smb2_ioctl_query_info() validates the PASSTHRU_FSCTL response payload before copying it to userspace. The payload offset and length both come from 32-bit fields. The bounds check currently adds OutputOffset and qi.input_buffer_length directly, so the addition can wrap in 32-bit arithmetic before the result is compared against the response buffer length. A malicious server can use a large OutputOffset and a small OutputCount to make the wrapped sum pass the bounds check. The later copy_to_user() then reads from io_rsp + OutputOffset, outside the response buffer. Use size_add() for the offset plus length check so overflow is treated as out of bounds.
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
- 2026-08-15 (2 months ago)source
- CVSS
- 8.1 high
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.64%, higher than 49.8% 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 |
|---|---|---|
| 5.5 | 5.10.261 | 175357ee0c59 |
| 5.5 | 5.15.212 | dbd126539c09 |
| 5.5 | 6.1.178 | 63feb687e89a |
| 5.5 | 6.6.145 | 160045fc943f |
| 5.5 | 6.12.97 | b30771b69eaf |
| 5.5 | 6.18.40 | 1627e7d5c9b0 |
| 5.5 | 7.1.5 | 1a638c55f2db |
| 5.5 | 7.2 | a4f27ad05539 |
| 5.4.69 | 0 | 0 |
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
- Exploitation requires processing a crafted SMB2 IOCTL response from a malicious SMB/CIFS server over TCP; the bug is in client-side parsing of attacker-controlled network protocol fields, not in a purely local code path.
- AC:LAttack complexity, low
- A malicious server can reliably supply OutputOffset and OutputCount values that wrap the 32-bit bounds check and pass validation, deterministically triggering the out-of-bounds copy_to_user() without races or special victim state.
- PR:LPrivileges required, low
- The PASSTHRU_FSCTL ioctl path requires CAP_SYS_ADMIN, which an unprivileged local user can obtain inside a user namespace and use to mount CIFS and issue CIFS_QUERY_INFO against an attacker-controlled server.
- UI:NUser interaction, none
- In the highest-impact scenario the attacker controls the full chain (user-namespace mount plus ioctl) and needs no separate victim action beyond their own exploitation steps.
- S:UScope, unchanged
- Impact is disclosure of kernel heap memory to the calling userspace process within the same kernel security authority; it does not cross VM, IOMMU, or sandbox boundaries.
- C:HConfidentiality impact, high
- The integer overflow bypasses bounds checking so copy_to_user() reads qi.input_buffer_length bytes from io_rsp plus attacker-chosen OutputOffset outside the SMB response buffer, leaking adjacent kernel memory to userspace.
- I:NIntegrity impact, none
- The flaw is an out-of-bounds kernel read copied to userspace; it does not modify kernel memory, corrupt metadata, or provide a write or code-execution primitive.
- A:HAvailability impact, high
- Reading far outside the allocated SMB response buffer can access unmapped kernel pages during copy_to_user(), causing a kernel fault, oops, or panic in addition to information disclosure.