Comprehensive Technical Analysis of CVE-2023-37717

CVE ID: CVE-2023-37717 CVSS Score: 9.8 (Critical) Vulnerability Type: Stack-Based Buffer Overflow Affected Function: fromDhcpListClient (HTTP request parameter page)

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1. Vulnerability Assessment & Severity Evaluation

Technical Overview

CVE-2023-37717 is a stack-based buffer overflow vulnerability in multiple Tenda router models, specifically within the fromDhcpListClient function. The flaw arises due to improper bounds checking when processing the page parameter in an HTTP request. An attacker can exploit this by sending a crafted input that exceeds the allocated stack buffer, leading to arbitrary code execution (ACE) or denial-of-service (DoS).

Severity Justification (CVSS 9.8 - Critical)

CVSS Metric	Value	Explanation
Attack Vector (AV)	Network (N)	Exploitable remotely over the network without authentication.
Attack Complexity (AC)	Low (L)	No specialized conditions required; straightforward exploitation.
Privileges Required (PR)	None (N)	No prior authentication needed.
User Interaction (UI)	None (N)	Exploit does not require user interaction.
Scope (S)	Unchanged (U)	Impact is confined to the vulnerable device.
Confidentiality (C)	High (H)	Successful exploitation could lead to full system compromise.
Integrity (I)	High (H)	Attacker can modify device configuration or execute arbitrary code.
Availability (A)	High (H)	Exploitation can crash the device or render it unresponsive.

Key Takeaways:

• Remote, unauthenticated exploitation makes this a high-risk vulnerability.
• Low attack complexity increases the likelihood of widespread exploitation.
• High impact on confidentiality, integrity, and availability (CIA triad).

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2. Potential Attack Vectors & Exploitation Methods

Exploitation Mechanism

1. Vulnerable Endpoint:
   • The fromDhcpListClient function processes HTTP requests containing a page parameter.
   • Example vulnerable request:

     GET /goform/DhcpListClient?page=[MALICIOUS_PAYLOAD] HTTP/1.1
     Host: <TARGET_IP>
     

2. Stack Overflow Trigger:
   • The page parameter is copied into a fixed-size stack buffer without proper length validation.
   • An attacker can send an oversized input (e.g., 1000+ bytes) to overflow the buffer, corrupting the return address on the stack.
3. Arbitrary Code Execution (ACE):
   • By carefully crafting the payload, an attacker can overwrite the return address to redirect execution to malicious shellcode (e.g., stored in an environment variable or another controlled memory region).
   • Common techniques:
     • Return-Oriented Programming (ROP) to bypass DEP/NX.
     • Shellcode injection via environment variables or HTTP headers.
4. Denial-of-Service (DoS):
   • Even if ACE is not achieved, a malformed payload can crash the device by corrupting the stack.

Exploitation Requirements

• Network Access: Attacker must be on the same network as the vulnerable router (LAN or WAN, depending on configuration).
• No Authentication: Exploitable without credentials.
• Public Exploits: Proof-of-concept (PoC) code is available in the referenced GitHub repository.

Post-Exploitation Impact

• Full Device Takeover: Execution of arbitrary commands with root privileges.
• Network Pivoting: Compromised router can be used as a foothold for lateral movement.
• Persistent Backdoor: Attacker may install malware or modify firmware.
• Traffic Interception: Man-in-the-middle (MITM) attacks via DNS spoofing or ARP poisoning.

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3. Affected Systems & Software Versions

Vulnerable Tenda Router Models & Firmware

Model	Firmware Version
F1202	V1.0BR_V1.2.0.20(408)
FH1202	V1.2.0.19_EN
AC10	V1.0
AC1206	V1.0
AC7	V1.0
AC5	V1.0
AC9	V3.0

Note:

• Other firmware versions may also be affected if they share the same vulnerable codebase.
• Tenda has not yet released an official advisory or patch for all affected models.

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4. Recommended Mitigation Strategies

Immediate Actions (Short-Term)

1. Network Segmentation:
   • Isolate vulnerable routers from critical internal networks.
   • Restrict WAN access to the router’s admin interface.
2. Disable Remote Management:
   • Ensure the router’s web interface is not exposed to the internet.
   • Use firewall rules to block external access to port 80/443.
3. Apply Workarounds:
   • If no patch is available, disable DHCP client listing via the router’s admin panel (if possible).
   • Monitor for unusual HTTP requests targeting /goform/DhcpListClient.

Long-Term Remediation

1. Firmware Updates:
   • Check Tenda’s official website for security patches.
   • If no patch is available, consider replacing the device with a supported model.
2. Intrusion Detection/Prevention (IDS/IPS):
   • Deploy Snort/Suricata rules to detect exploitation attempts:

     alert tcp any any -> $HOME_NET 80 (msg:"Tenda Router Stack Overflow Attempt (CVE-2023-37717)";
     flow:to_server,established; content:"/goform/DhcpListClient"; nocase;
     pcre:"/page=[^\x26]{500,}/i"; classtype:attempted-admin; sid:1000001; rev:1;)
     

3. Vulnerability Scanning:
   • Use tools like Nmap, OpenVAS, or Nessus to identify vulnerable devices:

     nmap -p 80 --script http-tenda-dhcp-overflow <TARGET_IP>
     

4. Zero Trust Network Access (ZTNA):
   • Implement strict access controls for router management.
   • Enforce multi-factor authentication (MFA) for admin access.

Vendor & Community Response

• Tenda’s Responsibility:
  • Release a patched firmware version addressing the buffer overflow.
  • Publish an official security advisory with mitigation guidance.
• Security Researcher Actions:
  • The GitHub repository (IoT-Vulns) provides PoC code, which should be used for defensive testing only.

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5. Impact on the Cybersecurity Landscape

Broader Implications

1. IoT Security Risks:
   • This vulnerability highlights the persistent insecurity of consumer-grade routers, which are often neglected in patch management.
   • Attackers can leverage such flaws to build botnets (e.g., Mirai variants) or conduct large-scale attacks.
2. Supply Chain Concerns:
   • Many Tenda routers are rebranded and sold under different names, increasing the attack surface.
   • Vulnerabilities in embedded firmware are difficult to patch, leading to long-term exposure.
3. Exploitation Trends:
   • In-the-wild exploitation is likely, given the low complexity and high impact.
   • Ransomware groups may target vulnerable routers for initial access.
4. Regulatory & Compliance Impact:
   • Organizations using affected routers may violate data protection laws (e.g., GDPR, CCPA) if compromised.
   • Critical infrastructure (e.g., SMBs, healthcare) relying on these devices face heightened risk.

Historical Context

• Similar vulnerabilities in Tenda routers (e.g., CVE-2021-31755, CVE-2020-10987) have been exploited in botnet campaigns.
• Real-world attacks (e.g., Moobot, Gafgyt) frequently target unpatched IoT devices.

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6. Technical Details for Security Professionals

Root Cause Analysis

1. Vulnerable Function (fromDhcpListClient):
   • Located in the router’s HTTP server binary (likely httpd or similar).
   • The function copies the page parameter into a fixed-size stack buffer without bounds checking.
   • Pseudocode Example:

     void fromDhcpListClient(char *page_param) {
         char buffer[256]; // Fixed-size stack buffer
         strcpy(buffer, page_param); // Unsafe copy (no length check)
         // ... rest of the function
     }
     

2. Stack Layout Exploitation:
   • A long page parameter (e.g., 1000+ bytes) overflows buffer, corrupting:
     • Saved frame pointer (EBP)
     • Return address (EIP/RIP)
   • Attacker can control execution flow by overwriting the return address.

Exploitation Steps (PoC)

1. Fuzz the page Parameter:
   • Send increasingly long inputs to identify the crash point.

   import requests
   target = "http://<ROUTER_IP>/goform/DhcpListClient"
   payload = "A" * 1000
   response = requests.get(target, params={"page": payload})
   

2. Determine Offset to EIP:
   • Use a cyclic pattern (e.g., pattern_create.rb in Metasploit) to find the exact offset.
   • Example:

     msf-pattern_create -l 1000
     

3. Craft ROP Chain (if DEP/NX is enabled):
   • Identify gadgets in the firmware binary (e.g., pop rdi; ret).
   • Use ROP to bypass ASLR and execute shellcode.
4. Deploy Shellcode:
   • Store shellcode in an environment variable or HTTP header.
   • Redirect execution to the shellcode location.

Reverse Engineering Insights

• Firmware Extraction:
  • Use Binwalk to extract the firmware:

    binwalk -e Tenda_Firmware.bin
    

• Binary Analysis:
  • Load the extracted httpd binary in Ghidra/IDA Pro.
  • Locate the fromDhcpListClient function and analyze the unsafe strcpy.
• Dynamic Analysis:
  • Use QEMU to emulate the router’s firmware for debugging.
  • Attach GDB to the running process to observe the crash.

Detection & Forensics

1. Log Analysis:
   • Check router logs for unusually long page parameters in HTTP requests.
   • Example log entry:

     [HTTP] GET /goform/DhcpListClient?page=AAAAAAAAAAAAAAAA... (1000+ chars)
     

2. Memory Forensics:
   • If a crash occurs, analyze the core dump for:
     • Corrupted stack frames
     • Shellcode signatures (e.g., \x90\x90\x90 NOP sleds)
3. Network Traffic Analysis:
   • Use Wireshark to capture and analyze malicious HTTP requests.

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Conclusion & Recommendations

Key Takeaways

• CVE-2023-37717 is a critical stack-based buffer overflow in multiple Tenda routers, enabling remote code execution.
• Exploitation is trivial and does not require authentication, making it a high-priority patching target.
• No official patches are currently available, necessitating workarounds and monitoring.

Action Plan for Security Teams

Priority	Action Item
Critical	Isolate vulnerable routers from production networks.
High	Deploy IDS/IPS rules to detect exploitation attempts.
Medium	Monitor for firmware updates from Tenda.
Low	Conduct a vulnerability scan to identify affected devices.

Final Recommendations

1. Assume compromise if vulnerable routers are exposed to untrusted networks.
2. Replace unsupported devices if no patches are forthcoming.
3. Enhance IoT security policies to include regular firmware updates and network segmentation.
4. Engage with Tenda’s support to urge a timely patch release.

This vulnerability underscores the critical need for robust IoT security practices, particularly in consumer and SMB environments where patch management is often overlooked. Security teams should proactively monitor for exploitation attempts and harden network defenses accordingly.