Comprehensive Technical Analysis of CVE-2025-69763

CVE ID: CVE-2025-69763 CVSS Score: 9.8 (Critical) Vulnerability Type: Stack-Based Buffer Overflow (Remote Code Execution) Affected Product: Tenda AX3 Router (Firmware v16.03.12.11) Vulnerable Component: formSetIptv (via vlanId parameter)

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1. Vulnerability Assessment & Severity Evaluation

Technical Overview

CVE-2025-69763 is a stack-based buffer overflow vulnerability in the Tenda AX3 router’s firmware, specifically in the formSetIptv function when processing the vlanId parameter. The flaw arises due to improper bounds checking when copying user-supplied input into a fixed-size stack buffer, leading to memory corruption and potential arbitrary code execution (RCE).

CVSS v3.1 Breakdown (Score: 9.8 - Critical)

Metric	Value	Explanation
Attack Vector (AV)	Network (N)	Exploitable remotely over the network.
Attack Complexity (AC)	Low (L)	No special conditions required; straightforward exploitation.
Privileges Required (PR)	None (N)	No authentication needed.
User Interaction (UI)	None (N)	No user interaction required.
Scope (S)	Unchanged (U)	Impact is confined to the vulnerable component.
Confidentiality (C)	High (H)	Full system compromise possible.
Integrity (I)	High (H)	Attacker can modify system behavior.
Availability (A)	High (H)	Denial-of-service (DoS) or persistent compromise.

Severity Justification

• Remote Exploitability: The vulnerability can be triggered via unauthenticated HTTP requests, making it highly dangerous in exposed network environments.
• Low Attack Complexity: No advanced techniques (e.g., heap grooming, ASLR bypass) are required for exploitation.
• High Impact: Successful exploitation grants root-level RCE, enabling full device takeover, lateral movement, or botnet recruitment (e.g., Mirai-like attacks).

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2. Potential Attack Vectors & Exploitation Methods

Attack Surface

The vulnerability is exposed via the Tenda AX3’s web interface, specifically in the IPTV configuration endpoint (/goform/formSetIptv). The vlanId parameter is improperly sanitized, allowing an attacker to overflow the stack buffer.

Exploitation Steps

1. Reconnaissance:

   • Identify vulnerable Tenda AX3 routers via Shodan, Censys, or mass scanning (e.g., http.title:"Tenda AX3").
   • Confirm firmware version (16.03.12.11) via /goform/getSysTool or HTTP headers.

2. Crafting the Exploit:

   • Payload Construction:
     • The vlanId parameter expects a numeric value but lacks length validation.
     • An attacker can send an oversized input (e.g., 1000+ bytes) to overflow the stack buffer.
     • Example malicious request:

       POST /goform/formSetIptv HTTP/1.1
       Host: <TARGET_IP>
       Content-Type: application/x-www-form-urlencoded
       Content-Length: <LENGTH>
       
       vlanId=<MALICIOUS_PAYLOAD>&other_params=...
       

   • Control Flow Hijacking:
     • The overflow corrupts the return address on the stack, allowing redirection to attacker-controlled shellcode.
     • Return-Oriented Programming (ROP) may be required if NX (No-Execute) bit is enabled.

3. Post-Exploitation:

   • Remote Code Execution: Execute arbitrary commands (e.g., telnetd, reverse shell).
   • Persistence: Modify firmware or install backdoors (e.g., cron jobs, iptables rules).
   • Lateral Movement: Pivot to internal networks if the router is used as a gateway.

Proof-of-Concept (PoC) Considerations

• Stack Layout Analysis:
  • Reverse-engineer the firmware (e.g., using Ghidra, IDA Pro) to identify:
    • Buffer size allocated for vlanId.
    • Stack canary presence (likely absent in embedded devices).
    • Function prologue/epilogue for ROP gadgets.
• Shellcode Development:
  • MIPS/ARM shellcode (depending on router architecture) for:
    • Spawning a reverse shell (/bin/sh).
    • Disabling firewall rules.
    • Downloading additional malware.

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3. Affected Systems & Software Versions

Vulnerable Product

• Device: Tenda AX3 (Wi-Fi 6 Router)
• Firmware Version: 16.03.12.11 (confirmed vulnerable)
• Likely Affected Versions:
  • Earlier versions in the 16.03.xx.xx branch may also be vulnerable (requires verification).
  • Later versions (if any) may have patched the issue (no official advisory yet).

Deployment Context

• Consumer & SOHO Networks: Common in home and small business environments.
• Exposure Risks:
  • Internet-facing routers (e.g., misconfigured port forwarding, UPnP).
  • Internal networks (if an attacker gains foothold via phishing or other exploits).

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4. Recommended Mitigation Strategies

Immediate Actions

Mitigation	Description	Effectiveness
Firmware Update	Apply the latest Tenda AX3 firmware (if available).	High (if patch exists)
Network Segmentation	Isolate the router from critical internal networks.	Medium (limits lateral movement)
Disable Remote Management	Restrict web interface access to LAN-only.	High (blocks external attacks)
Firewall Rules	Block inbound traffic to port 80/443 from untrusted sources.	Medium (reduces attack surface)
Intrusion Detection/Prevention (IDS/IPS)	Deploy signatures to detect exploitation attempts (e.g., Suricata rules).	Medium (detects but may not prevent)

Long-Term Recommendations

1. Vendor Engagement:

   • Monitor Tenda’s official security advisories for patches.
   • Request a CVE patch timeline if no updates are available.

2. Alternative Firmware:

   • Consider OpenWRT/DD-WRT (if supported) for better security controls.

3. Automated Vulnerability Scanning:

   • Use tools like Nessus, OpenVAS, or Nuclei to detect vulnerable devices.

4. Zero Trust Network Access (ZTNA):

   • Implement software-defined perimeters to limit router exposure.

5. User Awareness:

   • Educate users on router security best practices (e.g., changing default credentials, disabling WPS).

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5. Impact on the Cybersecurity Landscape

Threat Actor Motivations

• Botnet Recruitment: Vulnerable routers are prime targets for Mirai, Mozi, or Gafgyt variants.
• Initial Access: Attackers may use compromised routers as pivot points into corporate networks.
• Data Exfiltration: Routers can be used to sniff traffic or redirect users to malicious sites.

Broader Implications

• Supply Chain Risks: Tenda routers are widely deployed in emerging markets, increasing the attack surface.
• IoT Security Challenges: Highlights persistent issues in embedded device security (e.g., lack of ASLR, stack canaries).
• Regulatory Scrutiny: May prompt stricter IoT security standards (e.g., UK’s PSTI Act, EU Cyber Resilience Act).

Historical Context

• Similar vulnerabilities (e.g., CVE-2021-31755, CVE-2020-10987) have led to large-scale botnet infections.
• Exploit-as-a-Service (EaaS) models may emerge, lowering the barrier for less skilled attackers.

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6. Technical Details for Security Professionals

Root Cause Analysis

• Vulnerable Function: formSetIptv (likely in /bin/httpd or /bin/webs).
• Code Snippet (Hypothetical):

  void formSetIptv() {
      char vlanId[32]; // Fixed-size stack buffer
      strcpy(vlanId, get_param("vlanId")); // Unsafe copy (no bounds check)
      // ... further processing
  }
  

• Exploitation Primitive:
  • Stack Smashing: Overwrite the return address to hijack execution flow.
  • Shellcode Placement: If the buffer is executable, inject shellcode directly.

Exploitation Requirements

Requirement	Details
Architecture	Likely MIPS/ARM (common in Tenda routers).
Memory Protections	Likely absent (no ASLR, NX, stack canaries).
Debugging	Use QEMU + GDB for dynamic analysis.
Firmware Extraction	Tools: binwalk, firmware-mod-kit, Ghidra.

Detection & Forensics

• Network Signatures:
  • Unusually long vlanId parameters in HTTP POST requests.
  • Unexpected shell commands in logs (e.g., wget, curl, telnetd).
• Memory Forensics:
  • Check for corrupted stack frames in crash dumps.
  • Look for ROP gadgets in memory.

Advanced Exploitation Techniques

• Return-to-libc: If NX is enabled, chain libc functions (e.g., system()).
• Heap Spraying: If stack exploitation is unreliable, combine with heap corruption.
• Persistent Backdoors: Modify /etc/init.d/rc.local or /etc/crontab.

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Conclusion

CVE-2025-69763 represents a critical remote code execution vulnerability in Tenda AX3 routers, posing significant risks to consumer and SOHO networks. Given the low complexity of exploitation and high impact, immediate mitigation is essential. Security teams should:

1. Patch or replace vulnerable devices as soon as updates are available.
2. Monitor for exploitation attempts using IDS/IPS and network logs.
3. Assume compromise if indicators of attack (IoAs) are detected and perform forensic analysis.

The vulnerability underscores the urgent need for improved IoT security standards and vendor accountability in firmware development. Organizations should adopt a defense-in-depth strategy to mitigate risks from embedded device vulnerabilities.

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References:

• MITRE CVE Entry
• Tenda AX3 Firmware Analysis (Notion)
• OWASP IoT Security Guidance