Look up another CVE · open CVE-2026-64191 in the interactive tracker
CVE-2026-64191
i2c: stub: Reject I2C block transfers with invalid length
Published 2026-07-20 (3 months ago) by the Linux kernel CNA. Subsystem drivers/i2c. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-64191 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 | 6.1.177-1 | Update the kernel and reboot. Fixed in 6.1.177-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.95-1 | Update the kernel and reboot. Fixed in 6.12.95-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.14-1 | Update the kernel and reboot. Fixed in 7.0.14-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.14-1 | Update the kernel and reboot. Fixed in 7.0.14-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The I2C_SMBUS_I2C_BLOCK_DATA case in stub_xfer() uses data->block[0] as the transfer length. The existing check only clamps it to avoid overrunning the chip->words[256] register array, but does not validate it against I2C_SMBUS_BLOCK_MAX (32), which is the limit of the union i2c_smbus_data.block buffer (34 bytes total). The driver is a development/test tool (CONFIG_I2C_STUB=m, not built by default) that must be loaded with a chip_addr= parameter. A local user with access to /dev/i2c-* can issue an I2C_SMBUS ioctl with I2C_SMBUS_I2C_BLOCK_DATA and data->block[0] > 32, causing stub_xfer() to read or write past the end of the union i2c_smbus_data.block buffer: BUG: KASAN: stack-out-of-bounds in stub_xfer (drivers/i2c/i2c-stub.c:223) Read of size 1 at addr ffff88800abcfd92 by task exploit/81 Call Trace: <TASK> stub_xfer (drivers/i2c/i2c-stub.c:223) __i2c_smbus_xfer (drivers/i2c/i2c-core-smbus.c:593) i2c_smbus_xfer (drivers/i2c/i2c-core-smbus.c:536) i2cdev_ioctl_smbus (drivers/i2c/i2c-dev.c:391) i2cdev_ioctl (drivers/i2c/i2c-dev.c:478) __x64_sys_ioctl (fs/ioctl.c:583) do_syscall_64 (arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) </TASK> The bug exists because i2c-stub implements .smbus_xfer directly, bypassing the I2C_SMBUS_BLOCK_MAX validation in i2c_smbus_xfer_emulated(). The I2C_SMBUS_BLOCK_DATA case in the same function correctly validates against I2C_SMBUS_BLOCK_MAX, but the I2C_SMBUS_I2C_BLOCK_DATA case does not. Fix by rejecting transfers with data->block[0] == 0 or data->block[0] > I2C_SMBUS_BLOCK_MAX with -EINVAL, consistent with both the I2C_SMBUS_BLOCK_DATA case in the same function and the I2C_SMBUS_I2C_BLOCK_DATA validation in i2c_smbus_xfer_emulated().
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.
drivers/i2c/i2c-stub.c
- What this is
- I2C/SMBUS STUB DRIVERMAINTAINERS section matched on drivers/i2c/i2c-stub.c · linux-i2c@vger.kernel.org · Maintained
- Kernel module
- i2c_stub
Check it on the machine
grep -w CONFIG_I2C_STUB /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 i2c_stubPrints 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, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormMnot built on amd64/cloud-amd64, arm64/arm64, arm64/cloud-arm64, arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le
- trixieMnot built on amd64/cloud-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- forky, sidMnot built on amd64/cloud-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_I2C_STUB
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
- 2026-07-20 (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 2.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/i2c
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.33 | 5.10.260 | 7e9072dbd5f2 |
| 2.6.33 | 5.15.211 | 21e87f336ac6 |
| 2.6.33 | 6.1.177 | 3fd225f3e4cd |
| 2.6.33 | 6.6.144 | 1c4ffe6b4f04 |
| 2.6.33 | 6.12.95 | 4bd8635f28c1 |
| 2.6.33 | 6.18.37 | 5f4d2bd028eb |
| 2.6.33 | 7.0.14 | 0526931b16e5 |
| 2.6.33 | 7.1 | 6036b5067a81 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4717-1 | 2026-08-05 | bullseye 5.10.262-1 | tracker |
| DLA-4700-1 | 2026-07-26 | bullseye 6.1.177-1~deb11u1 | 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:LAttack vector, local
- The vulnerable path is reached by a local process issuing I2C_SMBUS ioctls on an i2c-stub /dev/i2c-* character device; it is neither remotely nor physically reachable.
- AC:LAttack complexity, low
- Once i2c-stub is loaded, the attacker controls the address, direction, length, and register contents, making the corruption deterministic without a race. The non-default module configuration defines the vulnerable deployment rather than complicating exploitation within it.
- PR:LPrivileges required, low
- The attacker needs unprivileged local access to the applicable /dev/i2c-* node, but no capability or namespace-specific administrative privilege is checked anywhere along the ioctl path.
- UI:NUser interaction, none
- After the vulnerable adapter is configured, exploitation requires only attacker-issued ioctls and no action by another user.
- S:UScope, unchanged
- The corruption occurs within the host kernel and represents conventional local privilege escalation, without crossing a separate virtualization or hardware security authority.
- C:HConfidentiality impact, high
- An oversized block write reads up to 222 bytes beyond the 34-byte stack union and persists those bytes in attacker-readable stub registers, enabling substantial kernel-stack disclosure.
- I:HIntegrity impact, high
- An oversized block read writes up to 222 attacker-chosen bytes beyond the stack union because the attacker can prepopulate the stub registers, enabling control-data corruption and potential kernel code execution.
- A:HAvailability impact, high
- The controlled stack overwrite can corrupt stack canaries, return state, or other control data, causing a repeatable kernel oops or panic even when code execution is unsuccessful.