CVE-2026-31405: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-31405 Overview

A vulnerability has been discovered in the Linux kernel's DVB-NET subsystem, specifically within the handle_one_ule_extension() function. The flaw involves an out-of-bounds (OOB) read vulnerability in the ULE (Unidirectional Lightweight Encapsulation) extension header handling tables. The ule_mandatory_ext_handlers[] and ule_optional_ext_handlers[] arrays are declared with 255 elements (valid indices 0-254), but the index htype is derived from network-controlled data as (ule_sndu_type & 0x00FF), which produces a range of 0-255. When htype equals 255, an out-of-bounds read occurs on the function pointer table, potentially allowing the OOB value to be called as a function pointer.

Critical Impact

An attacker with network access to DVB systems could exploit this vulnerability to trigger an out-of-bounds read that may result in arbitrary code execution or system crash through a malicious function pointer dereference.

Affected Products

• Linux kernel (DVB-NET subsystem with ULE extension handling)

Discovery Timeline

• 2026-04-06 - CVE CVE-2026-31405 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-31405

Vulnerability Analysis

This vulnerability represents an out-of-bounds read condition that can lead to arbitrary function pointer invocation. The root issue lies in the ULE extension header processing code within the DVB-NET subsystem. The extension handler tables are designed to accommodate 255 entries (indices 0-254), but the type extraction logic using a bitmask operation (ule_sndu_type & 0x00FF) can produce values in the range 0-255.

When an attacker crafts a malicious network packet with ule_sndu_type set such that the masked value equals 255, the code attempts to access element 255 of a 255-element array (which only has valid indices 0-254). This results in reading memory beyond the array boundaries. Since this memory location is then potentially called as a function pointer, the vulnerability can lead to code execution if the attacker can influence the memory contents at that location, or at minimum cause a system crash.

The vulnerability is particularly concerning because the htype value is derived from network-controlled data, meaning a remote attacker can trigger this condition without local access to the system.

Root Cause

The root cause is a classic off-by-one error in array bounds checking. The ule_mandatory_ext_handlers[] and ule_optional_ext_handlers[] arrays are declared with 255 elements, but the index calculation allows for values up to 255 (inclusive). The missing bounds check before array access allows network-controlled data to cause an out-of-bounds memory read.

Attack Vector

The attack vector involves sending specially crafted DVB network packets to a system running the vulnerable Linux kernel with DVB-NET functionality enabled. The attacker would craft a SNDU (SubNetwork Data Unit) with a type field that, when masked with 0x00FF, produces the value 255. This causes the vulnerable code path to read past the end of the handler arrays.

When the out-of-bounds function pointer is dereferenced and called, it can lead to:

• Arbitrary code execution if memory at the out-of-bounds location contains a controlled value
• Kernel panic or system crash
• Denial of service through kernel instability

The fix adds explicit bounds checking on the htype value against the array size before accessing either handler table. SNDUs with out-of-range htype values are now discarded rather than processed.

Detection Methods for CVE-2026-31405

Indicators of Compromise

• Unexpected kernel panics or crashes related to DVB-NET subsystem
• System logs showing SNDU processing errors or memory access violations in handle_one_ule_extension()
• Anomalous DVB network traffic with unusual SNDU type values

Detection Strategies

• Monitor kernel logs for DVB-NET related crashes or memory access violations
• Implement network traffic analysis to detect malformed SNDU packets with type values that would produce index 255 when masked
• Deploy kernel-level monitoring for out-of-bounds memory access attempts in the DVB subsystem
• Use SentinelOne Singularity Platform for real-time kernel behavioral analysis and exploit detection

Monitoring Recommendations

• Enable enhanced logging for DVB-NET subsystem operations where applicable
• Configure alerts for kernel oops or panic events related to media drivers
• Monitor for unusual patterns in DVB network traffic that may indicate exploitation attempts

How to Mitigate CVE-2026-31405

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the bounds checking fix
• If immediate patching is not possible, consider disabling DVB-NET functionality if not required
• Review system exposure to potentially malicious DVB network traffic
• Enable kernel crash dump analysis to capture any exploitation attempts

Patch Information

Multiple patches have been released to address this vulnerability across different kernel branches. The fix adds a bounds check on the htype variable against the array size before accessing the ule_mandatory_ext_handlers[] or ule_optional_ext_handlers[] tables. Out-of-range values now result in the SNDU being discarded.

Available kernel patches:

• Kernel Git Commit 145e50c
• Kernel Git Commit 1a6da3d
• Kernel Git Commit 24d8771
• Kernel Git Commit 29ef43c
• Kernel Git Commit 8bde543
• Kernel Git Commit f2b65dc

Workarounds

• Disable DVB-NET kernel module if DVB functionality is not required: modprobe -r dvb_net
• Implement network-level filtering to block potentially malicious DVB traffic from untrusted sources
• Use firewall rules to restrict access to DVB network interfaces from untrusted networks
• Consider network segmentation to isolate systems running DVB-NET functionality

# Disable DVB-NET module if not required
sudo modprobe -r dvb_net

# Blacklist the module to prevent automatic loading
echo "blacklist dvb_net" | sudo tee /etc/modprobe.d/blacklist-dvb-net.conf

# Verify module is not loaded
lsmod | grep dvb_net