CVE-2025-53758

Executive Summary

CVE-2025-53758 exposes a critical security flaw in the Digisol DG-GR6821AC router, where hardcoded default administrative credentials are embedded in the device firmware. An attacker with physical access can extract the firmware, reverse-engineer the binary, and retrieve these credentials to gain unauthorized administrative control over the device. This vulnerability is classified under CWE-798 (Use of Hard-coded Credentials) and maps to MITRE ATT&CK tactic T1078.001 (Default Accounts). The CVSS score is 0.0 due to the requirement of physical access, but the impact on confidentiality, integrity, and availability is high once exploited. No public proof-of-concept (PoC) or exploit code is available, and the vendor has not released a patch.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a hardware/firmware issue specific to the Digisol DG-GR6821AC router.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Base Score: 0.0 (Note: The CVSS score is 0.0 due to the physical access requirement, but the impact is severe.)
• Attack Vector (AV): Physical (P) – The attacker must have physical access to the device.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No prior authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerability affects only the device.
• Confidentiality (C): High (H) – Full disclosure of device configuration and network data.
• Integrity (I): High (H) – Full control to modify device settings.
• Availability (A): High (H) – Potential to disrupt device operation.

Threat Level: High (due to the ease of exploitation once physical access is obtained and the high impact on device security).

Deep Dive & Mechanics

The vulnerability stems from the use of hardcoded default credentials (e.g., username admin and password admin or similar) stored in the firmware of the Digisol DG-GR6821AC router. The firmware is typically stored in flash memory and can be extracted via physical access methods such as:

• Connecting to the UART/JTAG headers on the PCB.
• Using a SPI flash programmer to dump the firmware chip.
• Booting the device into a recovery mode that allows firmware extraction.

Once the firmware binary is obtained, an attacker can use tools like binwalk, strings, or a hex editor to search for credential strings. The credentials are often stored in plaintext or obfuscated with simple encoding (e.g., Base64) in configuration files or binary blobs. After extracting the credentials, the attacker can log into the web management interface (typically at http://192.168.1.1 or similar) and gain full administrative access.

The attack does not require network access, only physical proximity to the device. This makes it particularly dangerous in scenarios where routers are deployed in unsecured locations (e.g., public Wi-Fi hotspots, hotel rooms, or shared offices).

Vulnerable vs. Patched Code

Since no patch is available, there is no patched code to compare. The vulnerable code is the firmware binary containing hardcoded credentials. A secure implementation would:

• Generate unique credentials during first boot.
• Force the user to set a strong password during initial setup.
• Store credentials in a secure, encrypted format (e.g., using a hardware security module or secure element).

Example of vulnerable firmware string extraction:

strings firmware.bin | grep -i "admin"

Output might show:

admin:admin
admin:password
admin:1234

Example of secure implementation (pseudo-code):

import hashlib, os
# On first boot, generate random password
password = os.urandom(16).hex()
hash = hashlib.sha256(password.encode()).hexdigest()
# Store hash in secure storage

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• Physical access to the Digisol DG-GR6821AC router.
• Tools: SPI flash programmer (e.g., CH341A), soldering iron, wires, and a computer with firmware analysis tools.

Steps:

1. Extract Firmware:
   • Open the router casing.
   • Identify the SPI flash chip (e.g., Winbond W25Q128).
   • Connect the SPI programmer to the chip (pins: CS, MISO, MOSI, CLK, VCC, GND).
   • Use flashrom to dump the firmware:

     flashrom -p ch341a_spi -r firmware.bin
     

2. Analyze Firmware:
   • Use binwalk to extract filesystems:

     binwalk -e firmware.bin
     

   • Search for credentials:

     strings firmware.bin | grep -E "(admin|password|passwd|login)"
     

3. Access Web Interface:
   • Connect to the router via Ethernet or Wi-Fi.
   • Open a browser and navigate to http://192.168.1.1.
   • Log in with the extracted credentials (e.g., admin:admin).
4. Post-Exploitation:
   • Change DNS settings to redirect traffic.
   • Extract Wi-Fi passwords.
   • Install backdoor firmware.

Blue Team (Defender)

Detection:

• Monitor for physical tampering (e.g., opened casing, connected probes).
• Use network monitoring to detect unauthorized administrative logins (e.g., multiple failed attempts followed by success).
• Implement device attestation (e.g., TPM) to verify firmware integrity.

Mitigation:

• Replace the router with a patched model or one that supports secure boot.
• If replacement is not possible, change the default credentials immediately after installation.
• Restrict physical access to the device (e.g., lock in a secure cabinet).
• Enable logging and alerting for administrative access.

Indicators of Compromise (IOCs)

• Network:
  • Unusual administrative login events from unknown MAC addresses.
  • Changes to DNS settings or routing tables.
• Host:
  • Firmware hash mismatch (compare with known good hash).
  • Presence of unauthorized SSH or Telnet sessions.
• Physical:
  • Tampered casing or exposed PCB headers.
  • Unusual voltage fluctuations on SPI lines.

Example IOC:

• Firmware MD5 hash: a1b2c3d4e5f6... (replace with actual hash if known)
• Default credential strings: admin:admin, admin:password

Detection Engineering

YARA Rule

rule CVE_2025_53758_Digisol_Default_Creds {
    meta:
        description = "Detects hardcoded default credentials in Digisol DG-GR6821AC firmware"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-53758"
    strings:
        $cred1 = "admin:admin" ascii wide nocase
        $cred2 = "admin:password" ascii wide nocase
        $cred3 = "admin:1234" ascii wide nocase
        $cred4 = "root:root" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: Detection of Default Credential Usage on Digisol Router
id: 8f9e7d6c-5b4a-3c2d-1e0f-9a8b7c6d5e4f
status: experimental
description: Detects successful login attempts using default credentials on Digisol DG-GR6821AC web interface
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: web
detection:
    selection:
        http.response.status_code: 200
        http.url: "/login.cgi"
        http.body: "admin:admin"
    condition: selection
falsepositives:
    - Legitimate administrative use if credentials were not changed
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-53758 Digisol Default Credential Login Attempt"; flow:to_server; content:"POST"; http_method; content:"/login.cgi"; http_uri; content:"admin:admin"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Change Default Credentials: Log into the router and change the admin password to a strong, unique password.
2. Disable Remote Management: If not needed, disable remote access to the web interface.
3. Update Firmware: Check the Digisol website for any firmware updates. If none, consider replacing the device.

Long-Term Solutions:

• Vendor Action: Digisol must release a firmware update that removes hardcoded credentials and implements secure boot.
• User Education: Train users to change default passwords immediately upon device installation.
• Physical Security: Place routers in locked enclosures to prevent physical tampering.

Workarounds:

• Use a firewall to restrict access to the router's management interface to trusted IPs only.
• Implement network segmentation to isolate the router from critical systems.

Valters IT
Securing Digital Frontiers