Comprehensive Technical Analysis of EUVD-2026-4124 (CVE-2025-69764)

Tenda AX3 Firmware Stack-Based Buffer Overflow in formGetIptv Function

1. Vulnerability Assessment and Severity Evaluation

Vulnerability Overview

EUVD-2026-4124 (CVE-2025-69764) is a critical stack-based buffer overflow vulnerability in Tenda AX3 router firmware v16.03.12.11, specifically within the formGetIptv function. The flaw arises from improper bounds checking when processing the stbpvid parameter, leading to memory corruption and potential remote code execution (RCE).

CVSS 3.1 Severity Analysis

Metric	Value	Explanation
Attack Vector (AV)	Network (N)	Exploitable remotely over the network without physical access.
Attack Complexity (AC)	Low (L)	No specialized conditions required; straightforward exploitation.
Privileges Required (PR)	None (N)	No authentication or elevated privileges needed.
User Interaction (UI)	None (N)	Exploitation does not require user action.
Scope (S)	Unchanged (U)	Impact is confined to the vulnerable component (router firmware).
Confidentiality (C)	High (H)	Successful exploitation could lead to full system compromise.
Integrity (I)	High (H)	Attacker can modify memory, execute arbitrary code, or alter device behavior.
Availability (A)	High (H)	Exploitation may crash the device or render it inoperable.

Base Score: 9.8 (Critical) The vulnerability is remotely exploitable without authentication, making it a high-priority threat for network security teams. The CVSS vector (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) confirms its maximum impact on confidentiality, integrity, and availability.

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2. Potential Attack Vectors and Exploitation Methods

Attack Surface

The vulnerability is exposed via HTTP requests to the Tenda AX3 router’s web interface, specifically in the IPTV configuration endpoint. The formGetIptv function processes the stbpvid parameter without proper input validation, leading to a stack-based buffer overflow.

Exploitation Steps

1. Reconnaissance

   • Attacker identifies a vulnerable Tenda AX3 router (firmware v16.03.12.11) via:
     • Shodan/Censys scans (searching for Tenda AX3 HTTP banners).
     • Masscan/Nmap to detect open HTTP (80/443) ports.
     • Default credentials brute-forcing (if enabled).

2. Crafting the Exploit

   • The attacker sends a maliciously crafted HTTP POST request to the /goform/formGetIptv endpoint with an oversized stbpvid parameter.
   • The stbpvid buffer is copied into a fixed-size stack buffer without length checks, leading to stack corruption.
   • By carefully structuring the input, the attacker can:
     • Overwrite the return address on the stack.
     • Inject shellcode into executable memory regions (e.g., heap or stack).
     • Achieve arbitrary code execution with root privileges (since the web server typically runs as root).

3. Post-Exploitation

   • Remote Code Execution (RCE): Attacker gains full control over the router.
   • Persistence: Malware installation (e.g., Mirai-like botnet agents).
   • Lateral Movement: Pivoting into internal networks (e.g., via ARP spoofing or DNS hijacking).
   • Data Exfiltration: Intercepting/modifying network traffic (e.g., MITM attacks).
   • Denial of Service (DoS): Crashing the device by corrupting critical memory structures.

Exploitation Difficulty

• Low to Medium (depending on attacker skill level).
• Public PoC availability (as seen in the Notion reference) increases the risk of widespread exploitation.
• No authentication required, making it accessible to script kiddies and automated botnets.

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3. Affected Systems and Software Versions

Vulnerable Product

• Device: Tenda AX3 (Wi-Fi 6 Router)
• Firmware Version: v16.03.12.11 (confirmed vulnerable)
• Likely Affected Versions: All prior versions (if formGetIptv logic remains unchanged).

Potential Impact Scope

• Consumer & SOHO Networks: Tenda routers are widely used in home and small business environments.
• Enterprise Edge Cases: Some small enterprises may deploy Tenda routers for cost efficiency.
• IoT & Smart Home Ecosystems: Vulnerable routers could be exploited to compromise connected devices (e.g., cameras, smart plugs).

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4. Recommended Mitigation Strategies

Immediate Actions

Mitigation	Details	Effectiveness
Firmware Update	Apply the latest Tenda AX3 firmware patch (if available).	High (if vendor releases a fix)
Network Segmentation	Isolate the router in a DMZ or VLAN to limit lateral movement.	Medium (reduces attack surface)
Disable Remote Administration	Restrict web interface access to LAN-only.	High (prevents remote exploitation)
Firewall Rules	Block inbound HTTP/HTTPS to the router from the WAN.	High (stops external attacks)
Intrusion Detection/Prevention (IDS/IPS)	Deploy Snort/Suricata rules to detect exploit attempts.	Medium (detects but may not prevent)
Disable IPTV Functionality	If unused, disable the formGetIptv endpoint via router settings.	High (eliminates attack vector)

Long-Term Recommendations

1. Vendor Coordination

   • Monitor Tenda’s official security advisories for patches.
   • If no patch is available, consider replacing the device with a more secure alternative.

2. Network Hardening

   • Disable UPnP (prevents automatic port forwarding).
   • Change default credentials (use strong, unique passwords).
   • Enable WPA3 encryption (if supported) to secure Wi-Fi.

3. Threat Hunting & Monitoring

   • Log and analyze router access attempts (e.g., via SIEM integration).
   • Deploy honeypots to detect exploitation attempts.

4. Alternative Firmware (Advanced Users)

   • Consider OpenWRT/DD-WRT if the device is supported (may not be feasible for all users).

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5. Impact on the European Cybersecurity Landscape

Regulatory & Compliance Implications

• NIS2 Directive (EU 2022/2555): Critical infrastructure operators must ensure secure network devices; unpatched routers could lead to non-compliance.
• GDPR (EU 2016/679): If exploited, data exfiltration could result in personal data breaches, triggering reporting obligations and fines.
• ENISA Guidelines: The vulnerability aligns with ENISA’s "Threat Landscape for IoT" report, highlighting router security risks.

Threat Actor Exploitation

• Botnet Recruitment: Vulnerable routers are prime targets for Mirai, Mozi, or Gafgyt botnets.
• APT & Cybercrime: State-sponsored actors (e.g., APT29, Sandworm) or cybercriminals (e.g., TrickBot, Emotet) may exploit this for espionage or ransomware delivery.
• Supply Chain Risks: Compromised routers could be used in DDoS attacks or as proxies for malicious traffic.

Geopolitical & Economic Impact

• Critical Infrastructure: If deployed in healthcare, energy, or government sectors, exploitation could disrupt essential services.
• SMEs & Remote Work: Many European SMEs and remote workers rely on consumer-grade routers, increasing the attack surface.
• Cyber Insurance: Insurers may deny claims if devices are found to be unpatched, increasing financial risks for businesses.

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6. Technical Details for Security Professionals

Root Cause Analysis

• Vulnerable Function: formGetIptv (located in /bin/httpd or similar binary).
• Buffer Overflow Mechanism:
  • The stbpvid parameter is copied into a fixed-size stack buffer (e.g., char buf[256]) using an unsafe function (e.g., strcpy, sprintf).
  • No bounds checking allows an attacker to overflow the buffer, corrupting the stack frame and return address.
• Exploit Primitives:
  • Stack Smashing: Overwriting the saved return address to redirect execution.
  • ROP (Return-Oriented Programming): If ASLR/DEP is enabled, attackers may use ROP chains to bypass protections.
  • Shellcode Injection: If executable stack is enabled, arbitrary shellcode can be executed.

Proof-of-Concept (PoC) Analysis

Based on the Notion write-up, the PoC likely involves:

1. Sending a crafted HTTP POST request to /goform/formGetIptv with:

   POST /goform/formGetIptv HTTP/1.1
   Host: <ROUTER_IP>
   Content-Type: application/x-www-form-urlencoded
   Content-Length: <LENGTH>
   
   stbpvid=<MALICIOUS_PAYLOAD>
   

2. Payload Construction:
   • Junk Data: Fills the buffer until the return address.
   • Overwritten Return Address: Points to shellcode or a ROP gadget.
   • Shellcode: Typically a reverse shell or busybox backdoor.

Reverse Engineering & Exploitation

1. Firmware Extraction:

   • Use binwalk to extract the firmware:

     binwalk -e Tenda_AX3_V16.03.12.11.bin
     

   • Locate the httpd binary and analyze with Ghidra/IDA Pro.

2. Vulnerable Code Snippet (Pseudocode):

   void formGetIptv() {
       char stbpvid[256];  // Fixed-size stack buffer
       char *user_input = get_http_param("stbpvid");  // Untrusted input
       strcpy(stbpvid, user_input);  // UNSAFE: No length check
       // ... rest of the function
   }
   

3. Exploit Development:

   • Determine Buffer Size: Fuzz the stbpvid parameter to find the crash point.
   • Control EIP/RIP: Overwrite the return address to gain control.
   • Bypass Protections:
     • ASLR: Leak memory addresses via information disclosure.
     • DEP/NX: Use ROP chains to execute code.
     • Stack Canaries: If present, brute-force or leak the canary.

4. Post-Exploitation:

   • Privilege Escalation: Since httpd often runs as root, no further escalation is needed.
   • Persistence: Modify startup scripts (e.g., /etc/init.d/rc.local) to maintain access.
   • Lateral Movement: Scan the internal network for other vulnerable devices.

Detection & Forensics

• Network Signatures:
  • Snort Rule:

    alert tcp any any -> $HOME_NET 80 (msg:"Tenda AX3 formGetIptv Buffer Overflow Attempt"; flow:to_server,established; content:"POST /goform/formGetIptv"; nocase; content:"stbpvid="; nocase; pcre:"/stbpvid=[^\x26]{300,}/"; classtype:attempted-admin; sid:1000001; rev:1;)
    

• Log Analysis:
  • Check router logs (/var/log/httpd.log) for unusually long stbpvid parameters.
  • Monitor for unexpected reboots (indicative of crashes due to memory corruption).
• Memory Forensics:
  • Use Volatility to analyze memory dumps for shellcode execution.
  • Look for unexpected processes (e.g., /bin/sh, nc, busybox).

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Conclusion & Recommendations

EUVD-2026-4124 (CVE-2025-69764) is a critical remote code execution vulnerability in Tenda AX3 routers, posing significant risks to European networks. Given its CVSS 9.8 score, lack of authentication requirements, and public PoC availability, immediate action is required to mitigate exploitation.

Key Takeaways for Security Teams:

✅ Patch immediately if a firmware update is available. ✅ Disable remote administration and restrict web access to LAN-only. ✅ Monitor network traffic for exploit attempts using IDS/IPS rules. ✅ Segment networks to limit lateral movement if the router is compromised. ✅ Consider replacing the device if no patch is forthcoming.

Final Risk Assessment

Factor	Risk Level	Justification
Exploitability	High	Remote, unauthenticated, public PoC.
Impact	Critical	Full system compromise (RCE).
Likelihood	High	Widespread deployment, botnet interest.
Mitigation Feasibility	Medium	Requires firmware updates or network hardening.

Organizations must treat this vulnerability as a top priority to prevent botnet recruitment, data breaches, and network compromise. Proactive monitoring and rapid patching are essential to reducing exposure.