CVE-2026-53178: Linux Kernel Use-After-Free Vulnerability

CVE-2026-53178 Overview

CVE-2026-53178 is an integer underflow vulnerability in the Linux kernel's rtl8723bs staging Wi-Fi driver. The flaw resides in the rtw_mlme module, where the ie_length value was subtracted by fixed Information Element (IE) offsets without prior bounds validation. When ie_length is smaller than the offset being subtracted, the unsigned arithmetic wraps around, producing an extremely large length value. This can drive subsequent parsing logic into out-of-bounds memory access. Kernel maintainers resolved the issue by adding guards that verify ie_length is sufficiently large before performing the subtraction.

Critical Impact
Unsigned integer underflow in kernel Wi-Fi driver code can lead to out-of-bounds memory access and potential denial of service or memory corruption when parsing crafted 802.11 management frames.

Affected Products

Linux kernel drivers/staging/rtl8723bs Realtek RTL8723BS Wi-Fi driver
Kernel branches receiving the stable backports referenced in commits 542d65a6dbd9 and 88e994c57a79
Distributions shipping the rtl8723bs staging driver for embedded and SBC hardware

Discovery Timeline

2026-06-25 - CVE-2026-53178 published to NVD
2026-06-25 - Last updated in NVD database

Technical Details for CVE-2026-53178

Vulnerability Analysis

The vulnerability exists in the Multi-Layer Management Entity (MLME) handling code of the rtl8723bs staging driver. MLME routines parse 802.11 Information Elements from beacon, probe response, and association frames. The original code subtracted fixed IE header offsets from a variable named ie_length without first confirming that ie_length was greater than or equal to the offset. Because ie_length is an unsigned integer, a subtraction where the offset exceeds the actual length wraps to a near-maximum unsigned value. Downstream loops and copy operations then treat this wrapped value as a valid buffer size, reading or processing memory beyond the intended IE region.

Root Cause

The root cause is missing input validation [CWE-191 Integer Underflow] before unsigned arithmetic on attacker-influenceable length fields. The IE length is derived from frame data and can be set to any value from 0 to 255 per the 802.11 specification. Fixed IE offsets used in subtraction can exceed small ie_length values, producing the underflow. The patch introduces explicit comparisons that ensure ie_length is large enough before subtraction occurs.

Attack Vector

An attacker within wireless range of a vulnerable device can transmit malformed 802.11 management frames containing IE structures with abnormally small length fields. When the rtl8723bs driver parses these frames during scanning or association, the underflow occurs in kernel context. Exploitation does not require authentication or prior association, since management frame parsing happens before any link establishment. The realistic outcome is kernel memory disclosure or a system crash. See the patch commits for the specific code paths corrected: Kernel commit 542d65a6dbd9 and Kernel commit 88e994c57a79.

Detection Methods for CVE-2026-53178

Indicators of Compromise

Unexpected kernel oops or panic messages referencing rtw_mlme or rtl8723bs functions in dmesg or /var/log/kern.log.
Repeated wireless interface resets or driver reloads on systems using RTL8723BS chipsets.
Anomalous 802.11 management frames containing IE fields with length values below valid minimums captured in nearby wireless traffic.

Detection Strategies

Audit running kernel versions against the fixed commits to identify hosts still exposed to the underflow.
Enable KASAN (Kernel Address Sanitizer) on test builds to surface out-of-bounds reads originating from MLME IE parsing.
Monitor staging driver activity through ftrace or perf for abnormal call patterns in rtw_mlme functions during scan operations.

Monitoring Recommendations

Forward kernel logs to a centralized logging platform and alert on rtl8723bs crash signatures.
Track wireless driver crash counters exposed through /sys/kernel/debug on fleet endpoints.
Correlate Wi-Fi scan failures with kernel ring buffer entries to identify possible exploitation attempts.

How to Mitigate CVE-2026-53178

Immediate Actions Required

Update affected systems to a Linux kernel release containing commits 542d65a6dbd9 and 88e994c57a79.
Inventory devices using the rtl8723bs staging driver, including single-board computers and embedded appliances, and prioritize them for patching.
Restrict wireless scanning on untrusted networks until the patched kernel is deployed.

Patch Information

The fix was merged through the stable kernel tree under Kernel commit 542d65a6dbd9 and Kernel commit 88e994c57a79. Both commits add bounds checks that confirm ie_length is greater than or equal to the fixed IE offset before subtraction is performed. Apply the patched kernel through your distribution's update channel.

Workarounds

Blacklist the r8723bs kernel module on systems that do not require this Wi-Fi chipset by adding blacklist r8723bs to a file under /etc/modprobe.d/.
Disable wireless interfaces on affected hosts when operating in untrusted RF environments.
Replace RTL8723BS hardware with a chipset supported by a non-staging mainline driver where feasible.

bash

# Configuration example
# Prevent the vulnerable staging driver from loading
echo "blacklist r8723bs" | sudo tee /etc/modprobe.d/disable-rtl8723bs.conf
sudo modprobe -r r8723bs
sudo update-initramfs -u