CVE-2025-71137: Linux Kernel Shift-Out-of-Bounds Flaw

CVE-2025-71137 Overview

CVE-2025-71137 is a vulnerability in the Linux kernel affecting the octeontx2-pf network driver. The flaw occurs when the RX ring size (rx_pending) is not properly validated before use, allowing users to pass small or zero ring sizes via the ethtool -G command. This leads to UBSAN (Undefined Behavior Sanitizer) shift-out-of-bounds errors, which can cause system instability or undefined behavior.

Critical Impact

Improper input validation in the octeontx2-pf driver allows local users to trigger undefined behavior through manipulated ring size parameters, potentially causing system instability.

Affected Products

• Linux kernel (octeontx2-pf network driver)
• Systems using Marvell OcteonTX2 network processors
• Multiple stable kernel versions (patches available across various kernel branches)

Discovery Timeline

• 2026-01-14 - CVE-2025-71137 published to NVD
• 2026-01-19 - Last updated in NVD database

Technical Details for CVE-2025-71137

Vulnerability Analysis

The vulnerability exists in the octeontx2-pf driver, which handles network packet processing for Marvell OcteonTX2 processors. When a user configures the RX ring size using the ethtool -G interface, the driver fails to validate that the provided rx_pending value meets minimum size requirements. If a user supplies a value that is too small or zero, subsequent operations that depend on this value—particularly bitwise shift operations—can produce undefined behavior.

Shift-out-of-bounds errors occur when a shift operation attempts to shift a value by a number of bits that exceeds the size of the type or when the shift amount is negative. In this case, the undersized ring configuration propagates through the driver code and triggers UBSAN sanitizer warnings, indicating potential memory corruption or system instability.

Root Cause

The root cause is missing input validation in the octeontx2-pf driver's ring configuration handler. The driver did not enforce a minimum permitted length for the RX ring size before using it in subsequent calculations. This allows user-controlled input from ethtool -G to pass directly into shift operations without bounds checking, leading to undefined behavior when invalid values are processed.

Attack Vector

The attack requires local access to the system with sufficient privileges to modify network interface settings using ethtool. An attacker with such access can trigger the vulnerability by setting an invalid (small or zero) RX ring size parameter using the ethtool -G <interface> rx <value> command.

The exploitation path involves:

1. Attacker gains local access to a system with the octeontx2-pf driver loaded
2. Attacker uses ethtool -G to set the RX ring size to zero or a value below the minimum threshold
3. The driver processes the invalid value without proper validation
4. Shift operations using this value trigger UBSAN errors and undefined behavior

This vulnerability is a local privilege issue and does not have a known remote exploitation vector. The impact is limited to denial of service through system instability rather than code execution.

Detection Methods for CVE-2025-71137

Indicators of Compromise

• UBSAN error messages in kernel logs referencing octeontx2-pf driver and shift-out-of-bounds
• Kernel warnings or oops messages related to the otx2_set_ringparam function
• Unexpected network driver behavior or crashes following ethtool configuration changes
• System dmesg output containing "UBSAN: shift-out-of-bounds" with octeontx2 stack traces

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for UBSAN sanitizer warnings related to shift operations
• Audit ethtool command usage on systems with octeontx2-pf driver, particularly -G flag operations
• Deploy kernel runtime detection tools to catch undefined behavior sanitizer events
• Review system call logs for suspicious network interface configuration changes

Monitoring Recommendations

• Enable UBSAN in kernel builds to detect shift-out-of-bounds errors proactively
• Configure syslog alerting for kernel UBSAN messages to enable rapid response
• Monitor network interface configuration changes through auditd rules for ethtool invocations
• Implement baseline monitoring for octeontx2-pf driver behavior and performance metrics

How to Mitigate CVE-2025-71137

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the boundary validation fix
• Restrict ethtool access to trusted administrators only using appropriate permissions
• Monitor systems for UBSAN errors in kernel logs indicating exploitation attempts
• Consider temporarily restricting network interface configuration changes on affected systems

Patch Information

The Linux kernel maintainers have released multiple patches across stable kernel branches to address this vulnerability. The fix ensures that the RX ring size (rx_pending) is validated against a minimum permitted length before being used in driver operations.

Available kernel patches:

• Kernel Patch 442848e
• Kernel Patch 4cc4cfe4
• Kernel Patch 5d8dfa3
• Kernel Patch 658caf3
• Kernel Patch 85f4b0c
• Kernel Patch aa743b0
• Kernel Patch b23a2e15

Workarounds

• Restrict access to ethtool using filesystem permissions or SELinux/AppArmor policies
• Disable or unload the octeontx2-pf driver if not required for system operation
• Use kernel module parameters or driver configuration to enforce minimum ring sizes at load time
• Apply network namespace isolation to limit interface configuration access

# Restrict ethtool access to root only
chmod 750 /sbin/ethtool

# Verify current ring settings before applying updates
ethtool -g <interface>

# Monitor for UBSAN errors in kernel logs
dmesg | grep -i "UBSAN\|shift-out-of-bounds"