CVE-2026-53254: Linux Kernel Bluetooth RFCOMM RCE Flaw

CVE-2026-53254 Overview

CVE-2026-53254 is a Linux kernel vulnerability in the Bluetooth RFCOMM subsystem. The Multiplexer Control Channel (MCC) handlers cast skb->data to protocol-specific structures without first validating skb->len. A malicious remote Bluetooth device can send truncated MCC frames to trigger out-of-bounds reads in kernel memory. The issue affects the RFCOMM stack used for serial port emulation over Bluetooth and has been resolved upstream through patches that introduce skb_pull_data() validation before dereferencing socket buffer contents.

Critical Impact
A remote Bluetooth attacker within radio range can trigger kernel out-of-bounds reads by sending malformed MCC frames, potentially leaking kernel memory or causing instability.

Affected Products

Linux kernel — Bluetooth RFCOMM subsystem (multiple stable branches)
Systems with Bluetooth enabled and RFCOMM service exposed
Distributions shipping kernels prior to the fixes referenced in the stable tree commits

Discovery Timeline

2026-06-25 - CVE-2026-53254 published to NVD
2026-06-25 - Last updated in NVD database

Technical Details for CVE-2026-53254

Vulnerability Analysis

The vulnerability resides in the RFCOMM MCC handlers within the Linux kernel Bluetooth stack. RFCOMM provides a reliable serial port emulation protocol over the L2CAP layer, and MCC frames carry control messages such as parameter negotiation, modem status, and remote port negotiation (RPN).

The handlers receive a socket buffer (skb) containing untrusted remote data and cast skb->data directly to protocol-specific C structures. Because skb->len is never checked against the size of the target structure, a truncated frame causes the handler to read past the end of the valid buffer region. This results in an out-of-bounds read [CWE-125] in kernel space.

The rfcomm_recv_rpn() path requires nuanced handling because ETSI TS 07.10 permits a 1-byte RPN request that carries only the DLCI byte. The upstream fix validates the DLCI byte first, then validates the full structure only when len > 1, preserving protocol compliance while preventing buffer over-reads.

Root Cause

The root cause is missing input validation on attacker-controlled socket buffer length before structure casting. The handlers trusted the inbound frame layout instead of using skb_pull_data() to verify and consume the bytes required for each MCC command type.

Attack Vector

Exploitation requires an attacker within Bluetooth radio range of a target with an active RFCOMM listener. The attacker establishes an L2CAP connection to the RFCOMM PSM and transmits crafted MCC frames with truncated payloads. The malformed frames trigger out-of-bounds reads in the kernel, which can leak adjacent kernel memory contents into responses or destabilize the Bluetooth stack.

No verified public proof-of-concept code is available. Technical details are documented across the stable tree commits referenced in Kernel Git Commit 08b9c1f, Kernel Git Commit 0d6371, and related backports.

Detection Methods for CVE-2026-53254

Indicators of Compromise

Unexpected rfcommd or kernel Bluetooth subsystem crashes recorded in dmesg or journalctl -k
KASAN reports referencing rfcomm_recv_mcc, rfcomm_recv_rpn, or related handler symbols
Anomalous Bluetooth pairing or RFCOMM connection attempts from unknown peer addresses in btmon captures

Detection Strategies

Enable kernel address sanitizer (KASAN) on test systems to surface out-of-bounds reads in RFCOMM handlers during fuzzing
Monitor kernel logs for repeated RFCOMM protocol errors or oops messages tied to MCC frame parsing
Capture and inspect Bluetooth HCI traffic with btmon to identify malformed MCC frames with truncated length fields

Monitoring Recommendations

Forward kernel and bluetoothd logs to a central log platform and alert on RFCOMM-related faults
Inventory endpoints with the bluetooth and rfcomm kernel modules loaded to scope exposure
Track running kernel versions across the fleet and flag hosts not yet patched against CVE-2026-53254

How to Mitigate CVE-2026-53254

Immediate Actions Required

Apply the stable kernel updates that include the skb_pull_data() validation fixes for RFCOMM MCC handlers
Disable Bluetooth on systems where it is not required, including unloading the rfcomm and bluetooth kernel modules
Restrict RFCOMM service advertisement and require authenticated, paired connections only

Patch Information

The fix is distributed across multiple stable branches. Apply the kernel update from your distribution that incorporates the commits referenced by upstream, including Kernel Git Commit 08b9c1f, Kernel Git Commit 0d637136, Kernel Git Commit 1b070ac9, Kernel Git Commit 23882b82, Kernel Git Commit 3eabc6d4, Kernel Git Commit 7c15c7c2, and Kernel Git Commit 98377e6b. The patches replace direct casts of skb->data with skb_pull_data() calls that validate length before access.

Workarounds

Unload the rfcomm kernel module with modprobe -r rfcomm and blacklist it where Bluetooth serial services are not in use
Disable Bluetooth controllers via rfkill block bluetooth on hosts that do not require wireless connectivity
Set Bluetooth adapters to non-discoverable mode and limit pairing to known device addresses

bash

# Configuration example: disable RFCOMM and Bluetooth where unused
sudo rfkill block bluetooth
sudo systemctl disable --now bluetooth.service
echo 'blacklist rfcomm' | sudo tee /etc/modprobe.d/blacklist-rfcomm.conf
echo 'blacklist bluetooth' | sudo tee /etc/modprobe.d/blacklist-bluetooth.conf
sudo modprobe -r rfcomm bluetooth