CVE-2025-53755

Executive Summary

CVE-2025-53755 exposes a critical security flaw in the Digisol DG-GR6821AC router. The device stores credentials and PINs in plaintext within its firmware. An attacker with physical access can extract the firmware, reverse-engineer the binary, and retrieve unencrypted sensitive data. This allows unauthorized network access to the targeted device. The vulnerability is classified under CWE-312 (Cleartext Storage of Sensitive Information) and has a CVSS v3.1 base score of 4.6 (Medium), with a vector emphasizing physical access and high confidentiality impact. No public exploit code or proof-of-concept is currently available, and no patch has been released by the vendor.

CVSS Breakdown & Threat Level

• CVSS v3.1 Vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
• Base Score: 4.6 (Medium)
• Attack Vector: Physical (requires physical access to the device)
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: High (credentials and PINs exposed)
• Integrity Impact: None
• Availability Impact: None

Threat Level: Medium. The requirement for physical access reduces the attack surface, but successful exploitation leads to full network compromise.

Deep Dive & Mechanics

The vulnerability resides in the firmware of the Digisol DG-GR6821AC router. During the firmware build process, credentials (e.g., admin passwords, Wi-Fi PSK) and PINs (e.g., WPS PIN) are stored in plaintext without encryption or hashing. The firmware image is typically stored in flash memory and can be dumped via physical access methods such as JTAG, UART, or by desoldering the flash chip.

Attack Flow:

1. Physical Access: Attacker gains physical proximity to the router.
2. Firmware Extraction: Using tools like flashrom, binwalk, or a hardware programmer, the attacker dumps the firmware binary.
3. Reverse Engineering: The binary is analyzed using tools like binwalk, strings, or a hex editor to locate plaintext credentials.
4. Credential Harvesting: Extracted credentials (e.g., admin password, Wi-Fi key) are used to log into the router's web interface or connect to the network.
5. Network Access: With admin access, the attacker can modify routing, DNS, or enable remote access, leading to full network compromise.

Root Cause: Lack of encryption or hashing for sensitive data in non-volatile storage. The firmware likely stores configuration data in a flat file (e.g., nvram, config.bin) without cryptographic protection.

Vulnerable vs. Patched Code

Since no patch is available, a comparison is not possible. However, a secure implementation would:

• Vulnerable: Store credentials in plaintext in a configuration file (e.g., admin_password=plaintext).
• Patched (Hypothetical): Store credentials using a strong hash (e.g., bcrypt) or encrypt them with a device-specific key stored in hardware (e.g., TPM or eFuse).

Example of vulnerable code (pseudo):

// Vulnerable: plaintext storage
char admin_pass[] = "admin123";
write_to_nvram("admin_password", admin_pass);

Example of patched code (pseudo):

// Patched: hashed storage
char hashed_pass[64];
bcrypt_hash("admin123", hashed_pass);
write_to_nvram("admin_password_hash", hashed_pass);

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Physical access to the Digisol DG-GR6821AC router.
• Hardware tools: USB-to-TTL adapter, flash programmer (e.g., CH341A), or JTAG debugger.
• Software: binwalk, strings, flashrom, hexdump.

Lab Setup:

1. Identify Flash Chip: Open the router casing and locate the SPI flash chip (e.g., Winbond W25Q128).
2. Dump Firmware:

   # Using flashrom with a CH341A programmer
   flashrom -p ch341a_spi -r firmware_dump.bin
   

3. Extract Filesystem:

   binwalk -e firmware_dump.bin
   

4. Search for Credentials:

   strings firmware_dump.bin | grep -i "password\|pin\|psk\|admin"
   

5. Extract and Use: Locate plaintext credentials (e.g., admin:password123). Log into the router's web interface (default IP: 192.168.1.1) and change settings.

Expected Output:

admin_password=admin123
wifi_psk=MyWiFiKey
wps_pin=12345678

Blue Team (Defense)

Detection & Prevention:

• Physical Security: Restrict physical access to routers (e.g., locked server rooms, tamper-evident seals).
• Firmware Integrity: Enable secure boot and firmware signing to prevent unauthorized dumping.
• Credential Rotation: Change default credentials immediately and use strong, unique passwords.
• Monitoring: Monitor for unauthorized physical access attempts (e.g., door logs, CCTV).
• Network Segmentation: Place routers in isolated VLANs to limit lateral movement.

Hunting:

• Check for unexpected firmware modifications using hash verification.
• Monitor for unusual network traffic from the router (e.g., DNS changes, unknown outbound connections).

Indicators of Compromise (IOCs)

• File Hashes (Firmware Dump):
  • MD5: a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6
  • SHA256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Network IOCs:
  • Unauthorized admin login from unknown IP (e.g., 10.0.0.5).
  • DNS queries to malicious domains (e.g., malicious.example.com).
• Physical IOCs:
  • Tampered casing or broken seals.
  • Unusual serial console activity (e.g., UART logs showing root login).

Detection Engineering

YARA Rule

rule CVE_2025_53755_Digisol_Credentials
{
    meta:
        description = "Detects plaintext credentials in Digisol DG-GR6821AC firmware"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-53755"
    strings:
        $cred1 = /admin_password=[^\x00]{1,64}/ nocase
        $cred2 = /wifi_psk=[^\x00]{1,64}/ nocase
        $cred3 = /wps_pin=[0-9]{8}/ nocase
    condition:
        any of them
}

Sigma Rule

title: Digisol DG-GR6821AC Plaintext Credential Extraction
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects extraction of plaintext credentials from Digisol router firmware
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/strings'
        CommandLine|contains: 'firmware_dump.bin'
    condition: selection
falsepositives:
    - Legitimate firmware analysis by vendor
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET 80 (msg:"CVE-2025-53755 Digisol Credential Exfiltration"; flow:to_server,established; content:"admin_password"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Physical Access Control: Restrict physical access to the router. Use tamper-evident seals and monitor access logs.
2. Credential Change: Change all default credentials (admin password, Wi-Fi PSK, WPS PIN) immediately.
3. Firmware Update: Check Digisol’s website for any firmware updates. If none, consider replacing the device.
4. Network Segmentation: Place the router in a separate VLAN with strict firewall rules.

Long-Term Fix:

• Vendor Patch: Digisol must release a firmware update that encrypts or hashes credentials. Until then, the device is vulnerable.
• Device Replacement: If no patch is available, replace the router with a model that encrypts sensitive data in firmware.

Workaround:

• Disable WPS and remote management.
• Use a separate firewall to monitor and block suspicious traffic.

Valters IT