CVE-2025-68819: Linux Kernel Buffer Overflow Vulnerability

CVE-2025-68819 Overview

CVE-2025-68819 is an out-of-bounds vulnerability in the Linux kernel's dvb-usbdtv5100 media driver. The flaw resides in the dtv5100_i2c_msg() function, which processes I2C messages for DVB-T USB tuner devices. The function accepts a user-controlled rlen value without validating it against the size of the destination buffer st->data. When rlen exceeds sizeof(st->data), the kernel performs an out-of-bounds memory access. The upstream Linux kernel maintainers have resolved the issue by adding proper range checking to rlen before performing the I2C transfer.

Critical Impact
Improper bounds validation in the dtv5100_i2c_msg() function permits out-of-bounds memory access in kernel space, potentially leading to memory corruption or information disclosure.

Affected Products

Linux kernel dvb-usbdtv5100 media driver
Linux distributions shipping vulnerable kernel versions prior to the fix
Systems with DVB-T USB tuner support compiled into the kernel

Discovery Timeline

2026-01-13 - CVE-2025-68819 published to NVD
2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-68819

Vulnerability Analysis

The dtv5100_i2c_msg() function in the dtv5100 driver handles I2C message transfers between the kernel and the USB DVB-T tuner hardware. The function receives a read length parameter (rlen) that originates from message structures passed through the I2C subsystem. The driver copies the requested number of bytes into a fixed-size buffer field st->data belonging to the device state structure.

The driver does not compare rlen against sizeof(st->data) before performing the copy. When rlen exceeds the buffer size, the write or read operation extends past the allocated bounds. This results in an out-of-bounds access within kernel memory.

The consequences depend on the surrounding kernel allocation layout. Adjacent kernel objects can be overwritten or read, which may corrupt kernel state, leak sensitive information, or destabilize the system. The vulnerability is classified as an Out-of-Bounds Write [CWE-787] or Out-of-Bounds Read [CWE-125] condition.

Root Cause

The root cause is missing input validation. The dtv5100_i2c_msg() function trusts the caller-supplied rlen parameter without enforcing an upper bound. The fixed-size destination buffer st->data cannot accommodate arbitrary lengths, and the absence of a sanity check before the data transfer creates the out-of-bounds condition.

Attack Vector

Exploitation requires the ability to interact with the dtv5100 driver, typically through device file access or by attaching a crafted USB DVB-T device. An attacker capable of triggering an I2C transaction with an oversized rlen value can drive the driver into the vulnerable code path. The result is kernel memory corruption or unauthorized memory disclosure. See the Linux Kernel commit fixing CVE-2025-68819 for the patch details.

// No verified exploit code is published. The fix adds a bounds check
// comparing rlen against sizeof(st->data) before performing the I2C
// transfer in dtv5100_i2c_msg().

Detection Methods for CVE-2025-68819

Indicators of Compromise

Unexpected kernel oops or panic messages referencing dtv5100_i2c_msg in dmesg output
KASAN (Kernel Address Sanitizer) reports flagging out-of-bounds access in the dtv5100 driver
Anomalous USB device connection events involving DVB-T tuners on systems where such hardware is not expected

Detection Strategies

Audit loaded kernel modules with lsmod | grep dtv5100 to identify exposed systems
Enable KASAN on test kernels to surface out-of-bounds accesses during driver fuzzing
Monitor kernel logs for warnings from the dvb-usb subsystem and correlate with USB attachment events

Monitoring Recommendations

Collect kernel ring buffer messages via journalctl -k and forward them to a centralized log pipeline
Track USB device enumeration events and flag unknown vendor or product IDs binding to dvb-usb drivers
Alert on kernel crashes that occur shortly after USB attachment to systems with the dtv5100 driver loaded

How to Mitigate CVE-2025-68819

Immediate Actions Required

Apply the upstream Linux kernel patch for dtv5100_i2c_msg() or update to a kernel version that includes the fix
Unload the dtv5100 driver on systems that do not require DVB-T USB tuner functionality using modprobe -r dtv5100
Restrict physical USB access on systems where DVB-T tuner hardware is not used

Patch Information

The Linux kernel maintainers have published commits across multiple stable branches that add a range check on rlen before the I2C transfer. Refer to the upstream commits: commit 4a54d8fc, commit 61f214a8, commit ac92151f, commit b91e6aaf, commit c2305b4c, commit c2c293ea, and commit fe3e129a. Confirm that your distribution kernel pulls in the corresponding stable update.

Workarounds

Blacklist the dtv5100 module in /etc/modprobe.d/ to prevent it from loading on systems that do not require DVB-T USB tuner support
Apply USB device authorization policies to block unauthorized USB devices from binding to the kernel driver
Limit local user access on systems where the driver must remain loaded for operational reasons

bash

# Blacklist the dtv5100 driver to prevent it from loading
echo "blacklist dtv5100" | sudo tee /etc/modprobe.d/blacklist-dtv5100.conf
sudo modprobe -r dtv5100
sudo update-initramfs -u