CVE-2026-31627: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-31627 Overview

CVE-2026-31627 is a Linux kernel vulnerability in the i2c-s3c24xx driver. The driver fails to validate the size byte of an incoming System Management Bus (SMBUS) message before processing it. The first byte of an SMBUS message specifies its length and must fall within the 0..I2C_SMBUS_BLOCK_MAX range. Without this bounds check, the driver can operate on out-of-range length values, leading to memory corruption in kernel space. The fix mirrors the validation logic previously added to the i2c tegra driver in commit a6e04f05ce0b.

Critical Impact
A local attacker with low privileges can trigger out-of-bounds memory access in the kernel, resulting in privilege escalation, information disclosure, or denial of service.

Affected Products

Linux Kernel (multiple stable branches, including 3.10 and later)
Systems using the Samsung S3C24xx series I2C controller driver (i2c-s3c2410)
Embedded ARM platforms shipping the s3c24xx SoC family

Discovery Timeline

2026-04-24 - CVE-2026-31627 published to NVD
2026-04-27 - Last updated in NVD database

Technical Details for CVE-2026-31627

Vulnerability Analysis

The vulnerability resides in the Samsung S3C24xx I2C controller driver within the Linux kernel. When the driver handles an SMBUS block transaction, the first byte of the message buffer encodes the payload length. The driver consumes this length value to iterate over the buffer and transfer bytes across the I2C bus.

Because the size field is not validated against I2C_SMBUS_BLOCK_MAX (32 bytes), a malformed or attacker-influenced message can declare a length exceeding the allocated buffer. The driver then reads or writes past the end of the buffer, corrupting adjacent kernel memory.

Local exploitation is possible because the attack vector is local (AV:L) with low attack complexity and low privileges required, yielding high impact across confidentiality, integrity, and availability. The vulnerability is tracked under [CWE-NVD-noinfo] pending classification.

Root Cause

The root cause is missing input validation on user-influenced length data before it is used as a loop bound or memory offset. The driver trusted the embedded size byte without enforcing the SMBUS protocol's maximum block size constraint.

Attack Vector

An attacker requires local access and the ability to interact with the I2C subsystem, typically through /dev/i2c-* device nodes or a privileged user-space process that forwards crafted SMBUS transactions. By submitting an SMBUS block message with a size byte greater than I2C_SMBUS_BLOCK_MAX, the attacker forces the driver to access memory beyond the message buffer.

The out-of-bounds access occurs in kernel context, allowing manipulation of kernel data structures. Successful exploitation can yield code execution at ring 0 or reliable kernel panics.

No public proof-of-concept code is available. Refer to the upstream patches for technical details on the corrected validation flow.

Detection Methods for CVE-2026-31627

Indicators of Compromise

Unexpected kernel oops or panic messages referencing i2c-s3c2410 or s3c24xx_i2c_xfer in dmesg and /var/log/kern.log
Non-root processes opening /dev/i2c-* device nodes that have no legitimate need for direct I2C access
Kernel address sanitizer (KASAN) reports identifying out-of-bounds reads or writes inside the s3c24xx I2C driver

Detection Strategies

Audit kernel logs for I2C subsystem errors correlated with unprivileged process activity
Deploy runtime kernel integrity monitoring on embedded devices using the s3c24xx SoC family
Hunt for unexpected loaded kernel modules or driver behavior changes on affected ARM platforms

Monitoring Recommendations

Centralize kernel log telemetry from Linux endpoints and embedded systems for retrospective analysis
Track access patterns to I2C character devices and alert on access by non-privileged services
Correlate kernel panics with preceding user-space activity to identify exploitation attempts

How to Mitigate CVE-2026-31627

Immediate Actions Required

Apply the upstream Linux kernel patches referenced in the kernel.org commits as soon as a vendor build is available
Inventory all embedded and ARM systems using the Samsung S3C24xx I2C controller and prioritize them for patching
Restrict access to /dev/i2c-* device nodes to the root user or a dedicated trusted group

Patch Information

The Linux kernel maintainers committed the fix across multiple stable branches. Apply the patch from the appropriate stable tree:

The patch adds a bounds check ensuring the SMBUS message size is within 0..I2C_SMBUS_BLOCK_MAX before the driver processes it.

Workarounds

Tighten permissions on I2C device nodes by setting them to 0600 with root ownership
Blacklist the i2c-dev module on systems that do not require user-space I2C access
Apply mandatory access control policies (SELinux, AppArmor) to restrict which processes can issue I2C ioctls

bash

# Restrict I2C device node access to root only
chown root:root /dev/i2c-*
chmod 600 /dev/i2c-*

# Optionally blacklist user-space I2C access
echo "blacklist i2c-dev" | sudo tee /etc/modprobe.d/blacklist-i2c-dev.conf
sudo update-initramfs -u