CVE-2021-26675: Intel Connman Buffer Overflow Vulnerability

CVE-2021-26675 Overview

A stack-based buffer overflow vulnerability exists in the dnsproxy component of ConnMan versions before 1.39. This vulnerability allows network-adjacent attackers to execute arbitrary code on affected systems. ConnMan is a daemon for managing internet connections within embedded devices and is commonly found in automotive infotainment systems, IoT devices, and various Linux-based embedded platforms.

Critical Impact

Network-adjacent attackers can achieve remote code execution by exploiting the buffer overflow in dnsproxy, potentially compromising embedded systems including automotive infotainment systems and IoT devices.

Affected Products

• Intel ConnMan (versions before 1.39)
• Debian Linux 9.0 and 10.0
• openSUSE Leap 15.2

Discovery Timeline

• 2021-02-09 - CVE-2021-26675 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-26675

Vulnerability Analysis

The vulnerability is classified as CWE-787 (Out-of-bounds Write), specifically manifesting as a stack-based buffer overflow. The flaw resides in the DNS proxy functionality of ConnMan, which handles DNS queries and responses for connected devices. When processing specially crafted DNS responses, the dnsproxy component fails to properly validate the size of incoming data before copying it to a fixed-size stack buffer. This oversight allows an attacker to overflow the buffer boundaries and overwrite adjacent memory, including the return address.

The adjacent network attack vector means an attacker must be positioned on the same network segment as the target device, such as a shared Wi-Fi network or the same local area network. This is particularly concerning in scenarios like public Wi-Fi hotspots, shared office networks, or vehicle-to-vehicle communication where ConnMan is deployed.

Root Cause

The root cause of this vulnerability is insufficient bounds checking when handling DNS response packets in the dnsproxy module. The code copies DNS response data into a stack-allocated buffer without verifying that the incoming data length does not exceed the buffer's capacity. This classic memory corruption pattern allows attackers to write beyond the intended memory boundaries, corrupting stack data structures.

The fix, as documented in the kernel commit e4079a20f6, implements proper length validation before data copy operations occur.

Attack Vector

The attack requires adjacency to the target network. An attacker on the same network segment can craft malicious DNS responses that, when processed by the vulnerable dnsproxy component, trigger the buffer overflow condition. The exploitation chain typically involves:

1. Positioning on the same network as the vulnerable ConnMan device
2. Intercepting or responding to DNS queries from the target
3. Sending a crafted DNS response with an oversized payload
4. Overflowing the stack buffer to control execution flow
5. Achieving arbitrary code execution with the privileges of the ConnMan daemon

This vulnerability is part of the "TBONE" attack research documented by Kunnamon, which demonstrated practical exploitation scenarios against automotive systems. For detailed technical analysis, see the Kunnamon TBone Overview.

Detection Methods for CVE-2021-26675

Indicators of Compromise

• Anomalous DNS traffic patterns with oversized response packets targeting embedded devices
• Unexpected crashes or restarts of the ConnMan daemon (connmand)
• Evidence of memory corruption in system logs related to dnsproxy operations
• Unusual network activity from devices running ConnMan attempting to communicate with external hosts

Detection Strategies

• Monitor DNS traffic for response packets with abnormally large payloads destined for ConnMan-enabled devices
• Implement intrusion detection rules to identify malformed DNS responses on internal network segments
• Deploy endpoint monitoring to detect ConnMan process crashes or unexpected behavior patterns
• Review system logs for segmentation faults or memory access violations from connmand

Monitoring Recommendations

• Enable detailed logging for DNS proxy operations where possible
• Monitor for unusual patterns in local network DNS resolution
• Implement network segmentation to isolate IoT and embedded devices running ConnMan
• Deploy SentinelOne agents on Linux systems to detect exploitation attempts and memory corruption attacks

How to Mitigate CVE-2021-26675

Immediate Actions Required

• Update ConnMan to version 1.39 or later immediately
• Apply vendor-provided security patches for Debian, openSUSE, and other affected distributions
• Implement network segmentation to limit exposure of vulnerable embedded devices
• Monitor affected systems for signs of exploitation until patches can be applied

Patch Information

The vulnerability has been addressed in ConnMan version 1.39. The fix is documented in commit e4079a20f617a4b076af503f6e4e8b0304c9f2cb and implements proper bounds checking for DNS response handling.

Distribution-specific patches:

• Debian: Apply updates per Debian Security Advisory DSA-4847
• Debian LTS: See Debian LTS Announcement February 2021
• Gentoo: Apply patches per Gentoo GLSA 2021-07-29
• openSUSE: Reference SUSE Bug Report #1181751 for patch details

Workarounds

• Disable the DNS proxy functionality in ConnMan if not required for operations
• Implement strict network access controls to limit which devices can communicate with ConnMan-enabled systems
• Use firewall rules to restrict DNS traffic to trusted resolvers only
• Consider deploying an alternative DNS proxy solution while awaiting patch deployment

# Disable ConnMan DNS proxy functionality (if not required)
# Add to /etc/connman/main.conf:
[General]
DNSProxy=off

# Restart ConnMan service to apply changes
systemctl restart connman