CVE-2026-31626: Linux Kernel Use-After-Free Vulnerability

CVE-2026-31626 Overview

CVE-2026-31626 is an uninitialized memory use vulnerability in the Linux kernel's staging driver for the Realtek RTL8723BS wireless chipset. The vulnerability exists in the rtw_BIP_verify() function within drivers/staging/rtl8723bs/core/rtw_security.c, where only 6 bytes are copied to an 8-byte (u64) variable le_tmp64, leaving the remaining two bytes uninitialized. This can lead to unpredictable behavior and potential security implications when the uninitialized memory is subsequently used in cryptographic verification operations.

Critical Impact
An attacker on an adjacent network could potentially exploit this uninitialized memory condition to cause denial of service or bypass integrity checks in the Broadcast Integrity Protocol (BIP) verification process.

Affected Products

Linux Kernel (multiple versions with rtl8723bs staging driver)
Systems using Realtek RTL8723BS wireless chipsets
Embedded devices and IoT systems with affected kernel versions

Discovery Timeline

2026-04-24 - CVE CVE-2026-31626 published to NVD
2026-04-27 - Last updated in NVD database

Technical Details for CVE-2026-31626

Vulnerability Analysis

This vulnerability falls under CWE-908 (Use of Uninitialized Resource). The rtw_BIP_verify() function is responsible for verifying the integrity of broadcast management frames using the Broadcast Integrity Protocol (BIP), which is part of IEEE 802.11w Protected Management Frames (PMF) security. The function declares a u64 variable (le_tmp64) but only copies 6 bytes of data into it, as identified by the Smatch static analysis tool. The warning explicitly states: "not copying enough bytes for '&le_tmp64' (8 vs 6 bytes)."

When the remaining 2 bytes contain arbitrary stack or heap data, the resulting value used in subsequent cryptographic operations becomes unpredictable. This could lead to incorrect verification results, potential denial of service if the system crashes due to unexpected values, or in worst-case scenarios, bypass of integrity checks allowing malicious frames to be accepted.

Root Cause

The root cause is a failure to initialize the le_tmp64 variable before performing a partial memory copy operation. The function copies only 6 bytes (likely a truncated timestamp or sequence number from the wireless frame) into an 8-byte variable without first zeroing the entire variable. This is a common programming error in C where developers assume memory is zero-initialized or forget that partial writes leave residual data in the remaining bytes.

Attack Vector

The vulnerability requires adjacent network access, meaning an attacker must be within wireless range of the target system using an RTL8723BS wireless adapter. Exploitation does not require authentication or user interaction. An attacker could craft malicious wireless management frames that trigger the vulnerable code path. The uninitialized memory could cause:

Denial of Service: Unpredictable values may cause assertion failures, infinite loops, or crashes in the verification logic
Integrity Bypass: If uninitialized bytes happen to match expected values, malicious frames could pass verification
Information Leakage: Depending on how the value is used, kernel memory contents could potentially be inferred

The fix involves initializing le_tmp64 to zero at the start of the function, ensuring the upper 2 bytes are deterministically zero before the 6-byte copy operation occurs.

Detection Methods for CVE-2026-31626

Indicators of Compromise

Unexpected kernel crashes or panics in the wireless subsystem with stack traces referencing rtw_BIP_verify() or rtw_security.c
Anomalous wireless management frame processing errors in system logs
Unusual wireless disconnections or authentication failures on systems with RTL8723BS adapters
Smatch static analysis warnings indicating uninitialized memory in the rtl8723bs driver

Detection Strategies

Deploy kernel live patching or monitoring solutions that can detect calls to vulnerable code paths in the rtl8723bs driver
Implement wireless intrusion detection systems (WIDS) to identify potentially malicious management frames targeting PMF/BIP verification
Use memory sanitization tools (KASAN, KMSAN) in development/testing environments to catch uninitialized memory use
Monitor for kernel oops or panics with stack traces containing rtw_BIP_verify function references

Monitoring Recommendations

Enable kernel logging for wireless subsystem events and monitor for anomalies in BIP verification failures
Implement continuous vulnerability scanning to identify systems running affected kernel versions with the rtl8723bs driver loaded
Use endpoint detection solutions capable of monitoring kernel module behavior and detecting exploitation attempts

How to Mitigate CVE-2026-31626

Immediate Actions Required

Update the Linux kernel to a patched version containing the fix for this vulnerability
If immediate patching is not possible, consider disabling or blacklisting the rtl8723bs staging driver if not required
For critical systems, evaluate using alternative wireless adapters with mainline (non-staging) driver support
Apply wireless network segmentation to limit exposure from adjacent network attacks

Patch Information

The Linux kernel maintainers have released patches across multiple stable branches. The fix initializes the le_tmp64 variable to zero at the start of the rtw_BIP_verify() function, ensuring predictable behavior regardless of how many bytes are subsequently copied. Organizations should apply the relevant patch for their kernel version:

Workarounds

Blacklist the rtl8723bs module by adding blacklist rtl8723bs to /etc/modprobe.d/blacklist.conf if the wireless functionality is not required
Use a USB wireless adapter with a mainline kernel driver as an alternative to the RTL8723BS chipset
Implement network access controls to limit adjacent network exposure for affected systems
Enable 802.11w Protected Management Frames at the access point level to add an additional layer of protection

bash

# Blacklist the vulnerable driver if not needed
echo "blacklist rtl8723bs" | sudo tee /etc/modprobe.d/blacklist-rtl8723bs.conf
sudo update-initramfs -u
sudo reboot