CVE-2026-64191 Linux vulnerability
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().
Browse Linux security risksQuick answer
Linux should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- < 7e9072dbd5f2f17934751873450d2c22080ead80
- < 21e87f336ac6303fed54a69b1d0d79a23b25c8d0
- < 3fd225f3e4cd67ec8ddab1afed9da03c7c43537c
- < 1c4ffe6b4f04365485ed58d64c9bb86b46fc9037
- < 4bd8635f28c135a08aac6badcd7d9b5cdb34335f
- < 5f4d2bd028ebb6e4c09a9d64842546022321d4a7
- < 0526931b16e5a118d367b7bfce7d797e63f7ac69
- < 6036b5067a8199ba7a2dc7b377d4b9dd276d5f9e
- 2.6.33
Fixed versions
- 5.10.260
- 5.15.211
- 6.1.177
- 6.6.144
- 6.12.95
- 6.18.37
- 7.0.14
- 7.1
How to fix it
CVE-2026-64191 affects Linux and involves memory-safety failure. A crafted input may corrupt memory, crash the process, or enable code execution in the affected context. Prioritize deployments that process untrusted input, expose the affected feature, or hold sensitive data. Upgrade Linux to 5.10.260, 5.15.211, 6.1.177, 6.6.144, 6.12.95, 6.18.37, 7.0.14, 7.1 or a later vendor-supported fixed release.
- Inventory every deployment, device, package, plugin, container, build, and environment that uses Linux.
- Compare the installed version with the recorded affected range: < 7e9072dbd5f2f17934751873450d2c22080ead80, < 21e87f336ac6303fed54a69b1d0d79a23b25c8d0, < 3fd225f3e4cd67ec8ddab1afed9da03c7c43537c, < 1c4ffe6b4f04365485ed58d64c9bb86b46fc9037, < 4bd8635f28c135a08aac6badcd7d9b5cdb34335f, < 5f4d2bd028ebb6e4c09a9d64842546022321d4a7.
- Upgrade Linux to 5.10.260, 5.15.211, 6.1.177, 6.6.144, 6.12.95, 6.18.37, 7.0.14, 7.1 or a later vendor-supported fixed release.
- Until patched, limit untrusted files and peers, apply resource limits, and isolate the affected parser or service.
- Review configuration, roles, tokens, network paths, and exposed endpoints connected to Linux; remove access that is not required.
- Review application, system, proxy, and audit logs for requests and behavior linked to the affected feature and CVE.
- If exploitation is suspected, isolate affected assets, preserve evidence, rotate exposed credentials or keys, restore trusted data, and rebuild compromised systems before returning them to service.
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Verify the fix
- Confirm every affected asset now runs the fixed vendor-supported release or has the documented mitigation for CVE-2026-64191 in place.
- Use a safe regression test to confirm the affected memory-safety failure path no longer produces the vulnerable behavior.
- Confirm temporary access controls, endpoint restrictions, network blocks, and least-privilege settings remain effective after the update.
- Review post-remediation logs and rerun Fixnx plus the relevant package, dependency, firmware, browser, or product-specific security check.
- Document affected assets, versions, changes, validation evidence, reviewed logs, and any credential rotation, cleanup, or replacement completed.
Related categories
Related security risks
More published guidance from the same primary category.
Trusted references
FAQ
What is affected by CVE-2026-64191?
Linux versions listed as affected should be reviewed: < 7e9072dbd5f2f17934751873450d2c22080ead80, < 21e87f336ac6303fed54a69b1d0d79a23b25c8d0, < 3fd225f3e4cd67ec8ddab1afed9da03c7c43537c, < 1c4ffe6b4f04365485ed58d64c9bb86b46fc9037, < 4bd8635f28c135a08aac6badcd7d9b5cdb34335f, < 5f4d2bd028ebb6e4c09a9d64842546022321d4a7, < 0526931b16e5a118d367b7bfce7d797e63f7ac69, < 6036b5067a8199ba7a2dc7b377d4b9dd276d5f9e, 2.6.33.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.