Post 44 | Security Advisory: Unauthenticated Command Injection in D-Link DIR-868L B1 (CVE-2025-55583)

Author: Shaunak Ganorkar, Traboda Cyberlabs Pvt. Ltd.
Published: August 2025
CVE ID: CVE-2025-55583
Vendor: D-Link Systems, Inc.
Product: D-Link DIR-868L B1 Wireless Router
Firmware Affected: FW2.05WWB02
Firmware SHA-256: 545809e9851f26ea349a1681fbff4b1516b1af48d7364ac45b7016c901bdbaa8
Impact: Remote Unauthenticated Root-Level Command Execution
Severity: High
Status: Public

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Summary

The D-Link DIR-868L B1 router firmware (FW2.05WWB02) contains a critical unauthenticated command injection vulnerability in the fileaccess.cgi component of its web interface.

The parameter pre_api_arg is passed directly to system-level functions like system(), popen(), and execl() without authentication or sanitization. This allows a remote attacker with network access to execute arbitrary commands as root without requiring credentials or user interaction.

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Vulnerability Details

• Vulnerable Component: /dws/api/fileaccess.cgi
• Parameter: pre_api_arg
• Issue: Unvalidated input passed directly to shell-executing functions
• Attack Type: Remote (network-accessible interface)
• CWE IDs:
  • CWE-78: OS Command Injection
  • CWE-306: Missing Authentication for Critical Function
  • CWE-668: Exposure of Resource to Wrong Sphere

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Proof of Concept (PoC)

Static Analysis

1. Extracted firmware confirmed the presence of the fileaccess.cgi binary in the web root.

2. Identified the vulnerable pre_api_arg parameter using static analysis tools like strings and grep.

3. Located unsafe calls to system(), popen(), and execl() that accept attacker-controlled input.

4. Cross-referenced /dws/api/UploadFile in frontend files, confirming that the CGI endpoint is accessible.

5. Discovered /bin/ash, sh, and bash paths embedded in the binary.

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Attack Vector

• Unauthenticated Remote Access
  • Exploitable on LAN by default
  • Exploitable over WAN if remote access or port forwarding is enabled
• Exploit Steps
  1. Send a crafted HTTP request to /dws/api/fileaccess.cgi
  2. Inject arbitrary commands via the pre_api_arg parameter
  3. Gain root-level access on the device

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Impact

• Full device compromise on LAN or WAN
• Persistent backdoors via modified startup scripts
• Traffic interception or DNS hijacking
• Inclusion in botnet campaigns
• Lateral network compromise in home or enterprise setups

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Severity Justification

CVSS v3.1 Base Score: 8.8 (High)
Vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v4.0 Base Score: 9.8 (Critical)
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

This vulnerability is network-accessible, requires no authentication, and enables full root-level command execution, making it critically dangerous for both home and enterprise environments.

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Recommendations

For Users

• Disconnect vulnerable DIR-868L B1 routers from the internet immediately
• Disable remote administration and port forwarding
• Replace legacy hardware with models actively receiving updates

For Vendors

• Sanitize and validate all CGI input parameters
• Remove direct shell invocation from web binaries
• Drop root privileges for web-facing services
• Deprecate or patch legacy CGI interfaces

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Vendor Communication

• July 29, 2025: Initial disclosure sent to D-Link PSIRT with full technical documentation
• July 30, 2025: Vendor acknowledged and confirmed advisory is published under SAP10397

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Discoverer

Shaunak Ganorkar
Traboda Cyberlabs Pvt. Ltd.

🔗 https://www.cybermaya.in
🔗 https://www.linkedin.com/in/shaunakganorkar

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Disclaimer

This research is for educational and responsible disclosure purposes only. No unauthorized access was performed on live systems. Users should replace unsupported devices and adopt best security practices.