CVE-2025-38425: Linux Kernel I2C SMBUS Vulnerability

CVE-2025-38425 Overview

CVE-2025-38425 is a Linux kernel vulnerability in the i2c-tegra driver that fails to validate the message length returned by a device during an SMBus block read. When the reported length is zero or exceeds the maximum allowed bytes, the driver continues the read operation, leading to out-of-bounds memory access on affected NVIDIA Tegra platforms. The flaw affects the Linux kernel and Debian Linux distributions that ship the vulnerable driver. Exploitation requires local access with low privileges and can compromise confidentiality, integrity, and availability.

Critical Impact
A malicious or malfunctioning I2C peripheral can trigger out-of-bounds memory access in kernel space, enabling denial of service or potential kernel memory corruption on systems using the Tegra I2C driver.

Affected Products

Linux Kernel (multiple stable branches prior to the fix commits)
Debian Linux 11.0
NVIDIA Tegra-based platforms using the i2c-tegra driver

Discovery Timeline

2025-07-25 - CVE-2025-38425 published to the National Vulnerability Database (NVD)
2026-07-30 - Last updated in NVD database

Technical Details for CVE-2025-38425

Vulnerability Analysis

The vulnerability resides in the Tegra I2C controller driver at drivers/i2c/busses/i2c-tegra.c. During an SMBus block read transaction, the target device transmits a length byte that specifies how many additional data bytes will follow. The driver historically trusted this value without bounds checking.

SMBus block reads support a maximum of 32 data bytes per the SMBus specification. When a device returns a length of 0 or a value greater than I2C_SMBUS_BLOCK_MAX, the driver still proceeds to read the reported number of bytes into the caller's buffer. The result is either a malformed transaction or a write past the end of the kernel buffer allocated for the SMBus payload.

The fix adds an explicit length check in the block read code path. If the device-supplied length is zero or exceeds the SMBus block maximum, the driver aborts the transaction instead of continuing.

Root Cause

The root cause is missing input validation of an attacker-controlled length field received over the I2C bus. This is an input validation error that manifests as an out-of-bounds memory access when a malicious or faulty peripheral supplies an invalid length byte.

Attack Vector

Exploitation requires local access with low privileges to interact with the I2C subsystem, or physical or supply-chain control over an I2C peripheral connected to a Tegra host. An attacker who can attach or emulate a malicious SMBus device, or who can influence a peripheral's response over the I2C bus, can return a crafted length byte to trigger the flaw. The impact ranges from kernel panic to potential kernel memory corruption depending on the surrounding allocator state.

No public proof-of-concept exploit is available for this issue.

Detection Methods for CVE-2025-38425

Indicators of Compromise

Kernel oops or panic messages referencing tegra_i2c or i2c_smbus_xfer in dmesg or /var/log/kern.log
KASAN reports indicating out-of-bounds writes originating in the Tegra I2C driver
Unexpected reboots or hangs on Tegra-based devices during I2C peripheral enumeration

Detection Strategies

Inventory running kernel versions against the fix commits 3f03f77, 75a864f, a6e04f0, be5f6a6, and c39d1a9 to identify unpatched hosts
Monitor kernel logs on Tegra platforms for I2C transaction errors correlated with peripheral connect events
Enable KASAN in test builds to surface out-of-bounds accesses in the i2c-tegra driver during hardware validation

Monitoring Recommendations

Forward kernel logs from Tegra-based endpoints and edge devices to a centralized logging platform for anomaly review
Track uptime and crash counters on embedded Tegra deployments where physical tampering with I2C peripherals is possible
Alert on new or unauthorized I2C peripheral attachments in environments where peripherals are expected to be static

How to Mitigate CVE-2025-38425

Immediate Actions Required

Apply the upstream Linux kernel patches referenced by commits 3f03f77, 75a864f, a6e04f0, be5f6a6, and c39d1a9 from the Linux stable tree
Debian 11 users should install the kernel update described in the Debian LTS Security Announcement
Restrict local shell access on Tegra-based systems to trusted administrators until patching is complete

Patch Information

The fix is available across multiple Linux stable branches. Refer to the mainline commit and stable backports: Linux Kernel Commit 3f03f77, Linux Kernel Commit 75a864f, Linux Kernel Commit a6e04f0, Linux Kernel Commit be5f6a6, and Linux Kernel Commit c39d1a9. Debian users should track the Debian LTS advisory for distribution-specific package versions.

Workarounds

Unload the i2c-tegra kernel module on systems where the driver is not required using modprobe -r i2c_tegra
Physically secure Tegra devices to prevent attachment of untrusted SMBus or I2C peripherals
Blacklist untrusted I2C client drivers via /etc/modprobe.d/ to reduce the attack surface until patches are applied

bash

# Verify the running kernel and check for the Tegra I2C module
uname -r
lsmod | grep i2c_tegra

# Temporarily unload the driver where not required
sudo modprobe -r i2c_tegra

# Persistently blacklist the module until a patched kernel is installed
echo "blacklist i2c_tegra" | sudo tee /etc/modprobe.d/blacklist-i2c-tegra.conf
sudo update-initramfs -u