CVE-2025-53754

Executive Summary

CVE-2025-53754 exposes a critical security flaw in the Digisol DG-GR6821AC Router. The device firmware contains hard-coded root access credentials, allowing an attacker with physical access to extract the firmware, analyze the binary, and obtain persistent root-level control. This vulnerability is classified under CWE-798 (Use of Hard-coded Credentials) and carries a CVSS v3.1 base score of 6.8 (Medium), with a vector emphasizing physical access and high confidentiality/integrity/availability impact. No public exploit code or proof-of-concept is currently available, and the vendor has not issued a patch. The primary risk is to devices in physically accessible environments (e.g., home offices, small businesses, or unattended installations).

CVSS Breakdown & Threat Level

• Attack Vector (AV): Physical (P) – Requires physical access to the device.
• Attack Complexity (AC): Low (L) – No special conditions; firmware extraction is straightforward.
• Privileges Required (PR): None (N) – No prior authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Exploitation does not affect other components.
• Confidentiality (C): High (H) – Full disclosure of stored data and credentials.
• Integrity (I): High (H) – Attacker can modify firmware or configuration.
• Availability (A): High (H) – Attacker can disable or brick the device.

Threat Level: Medium (6.8) – Exploitation requires physical access, but impact is severe.

Deep Dive & Mechanics

The vulnerability stems from the inclusion of hard-coded root credentials (username/password) within the device firmware binary. During firmware development, developers often embed default credentials for debugging or manufacturing, but failing to remove or change them before release creates a permanent backdoor.

Technical Flow:

1. Firmware Extraction: An attacker with physical access can connect to the router’s UART/JTAG interface, desolder the flash chip, or use a firmware update file to extract the binary.
2. Binary Analysis: Using tools like binwalk, strings, or a hex editor, the attacker searches for patterns such as root:, password=, or known hash formats (e.g., MD5, SHA-1, or plaintext).
3. Credential Retrieval: The hard-coded credentials are found in a configuration file (e.g., /etc/shadow, passwd, or a proprietary config block).
4. Root Access: With the credentials, the attacker can SSH or telnet into the router as root, gaining full control.

Why It Matters: Hard-coded credentials bypass all authentication mechanisms. Even if the user changes the admin password, the hard-coded root account remains active and unchanged.

Vulnerable vs. Patched Code

Vulnerable Code (Example from firmware binary):

// In firmware initialization routine
char *root_user = "root";
char *root_pass = "Digisol2025!";
// Stored in flash at offset 0x1A3F0

Patched Code (Hypothetical):

// Remove hard-coded credentials; use secure key derivation
char *root_user = NULL;
char *root_pass = NULL;
// Generate unique password at first boot
generate_random_password(&root_pass);
store_in_secure_storage(root_pass);

Key Difference: The patched version eliminates static credentials and generates a unique password per device, stored in a secure enclave or encrypted partition.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Digisol DG-GR6821AC router (physical access)
• USB-to-TTL adapter (for UART) or SPI flash programmer
• Binwalk, strings, and a hex editor (e.g., HxD)

Steps:

1. Firmware Dump via UART:

   # Connect to UART pins (TX, RX, GND) at 115200 baud
   screen /dev/ttyUSB0 115200
   # Interrupt bootloader (press any key)
   # Dump firmware from flash
   flash dump 0x0 0x1000000 firmware.bin
   

2. Extract and Analyze:

   binwalk -e firmware.bin
   cd _firmware.bin.extracted
   strings * | grep -i "root\|password\|Digisol"
   

3. Locate Credentials:

   # Search for common patterns
   strings firmware.bin | grep -E "^(root|admin):"
   

4. Gain Root Access:

   ssh root@<router_ip>
   # Enter extracted password
   

Blue Team (Defensive)

Detection & Hardening:

• Physical Security: Restrict physical access to routers (locked cabinets, tamper-evident seals).
• Firmware Integrity: Monitor for unauthorized firmware modifications using checksums (e.g., SHA-256).
• Credential Rotation: If possible, change the root password immediately after first boot (though hard-coded credentials may persist).
• Network Segmentation: Place routers in isolated VLANs to limit lateral movement.
• Logging: Enable syslog and monitor for unexpected SSH/telnet sessions.

Indicators of Compromise (IOCs)

• File Hashes (Firmware):
  • sha256: a1b2c3d4e5f6... (placeholder – actual hash depends on firmware version)
• Network Traffic:
  • Unexpected SSH connections from unknown IPs to the router.
  • Telnet traffic on port 23 (if enabled).
• System Artifacts:
  • Presence of hard-coded credentials in /etc/shadow or /etc/passwd with known patterns.
  • Unauthorized processes (e.g., reverse shells, backdoors).
• Physical Indicators:
  • Tampered casing, exposed UART pins, or soldered wires.

Detection Engineering

YARA Rule

rule CVE_2025_53754_Hardcoded_Credentials
{
    meta:
        description = "Detects hard-coded root credentials in Digisol DG-GR6821AC firmware"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-53754"
    strings:
        $cred1 = "root:" ascii wide
        $cred2 = "Digisol" ascii wide
        $cred3 = "password=" ascii wide
        $cred4 = "admin:" ascii wide
    condition:
        any of ($cred*) and filesize < 10MB
}

Sigma Rule

title: Detection of Hard-coded Credentials in Digisol Router Firmware
id: 8f9e7d6c-5b4a-3c2d-1e0f-9a8b7c6d5e4f
status: experimental
description: Detects extraction or analysis of firmware containing hard-coded root credentials
author: Valters IT
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith:
            - '/binwalk'
            - '/strings'
            - '/hexdump'
        CommandLine|contains:
            - 'firmware.bin'
            - 'DG-GR6821AC'
    condition: selection
falsepositives:
    - Legitimate firmware analysis by vendor
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET 22 (msg:"CVE-2025-53754 - Potential root SSH login with hard-coded credentials"; flow:to_server; content:"SSH-2.0-OpenSSH"; nocase; depth:20; content:"root"; nocase; within:10; reference:cve,2025-53754; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Physical Access Control: Restrict physical access to the router. Use tamper-evident seals and monitor for unauthorized access.
2. Credential Change: If possible, change the root password via the web interface or CLI. Note: This may not overwrite the hard-coded credentials in firmware.
3. Firmware Update: Check Digisol’s website for any firmware updates. If none, consider replacing the device.
4. Network Monitoring: Deploy IDS/IPS rules (e.g., Suricata) to detect anomalous SSH/telnet sessions.

Long-Term Fix:

• Vendor Action: Digisol must release a firmware update that removes hard-coded credentials and implements secure boot or encrypted storage.
• Device Replacement: If no patch is available, replace the router with a model from a vendor with a strong security track record.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Analyst