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D-Link DIR-816L Stack-Based Buffer Overflow

D-Link DIR-816L

CVE-2025-13189 Stack Buffer Overflow Remote Code Execution

Overview

A high-severity stack-based buffer overflow vulnerability in the D-Link DIR-816L (firmware 2_06_b09_beta) allows remote attackers to trigger memory corruption through the SERVER_ID or HTTP_SID parameters inside the gena.cgi script. The flaw exists in the genacgi_main function, resulting in a classic stack overflow that may enable remote code execution or device takeover. The product is End-of-Life, and no patches will be issued.

Technical Specifications

Attribute Details
CVE ID CVE-2025-13189
Vulnerability Type Stack-Based Buffer Overflow (CWE-121)
Attack Vector Network (Remote)
Authentication None required
Complexity Low
User Interaction Not required
Affected Component gena.cgi → genacgi_main
Exploit Status Public exploit available
Firmware Status End-of-Life (EoL)

Affected Products

  • D-Link DIR-816L
  • Firmware: 2_06_b09_beta
  • Status: End-of-Life – No future security patches

Attack Scenario

  1. Attacker sends an HTTP request to the router’s gena.cgi endpoint.
  2. The request contains an overly long SERVER_ID or HTTP_SID parameter.
  3. The input overflows a fixed-size stack buffer inside genacgi_main.
  4. The attacker may gain remote code execution or cause a crash.

  5. Upon compromise, the router can be used for:

  6. Lateral movement

  7. Traffic interception
  8. Botnet activity
  9. Persistent network access

Potential Access Points

  • Router admin interface exposed to the Internet
  • Local network access
  • Compromised internal hosts sending malicious HTTP requests
  • ISP-deployed consumer networks

Impact Assessment

  • Router configuration tampering
  • Injection of malicious settings
  • Overwriting of system memory
  • Potential malicious firmware modification
  • Interception of user traffic
  • Exposure of credentials and network metadata
  • Reconnaissance into LAN network layout
  • Router crash or reboot loop
  • Loss of internet connectivity
  • DoS through repeated exploitation
  • Router takeover for botnets
  • Lateral movement into sensitive LAN systems
  • Use as a pivot point for further attacks
  • Compromise of home or small business perimeter security

Mitigation Strategies

Network Isolation

  • Do not expose the DIR-816L management interface to the Internet
  • Place the device behind a firewall with strict rules
  • Use VLAN segmentation to isolate the router from critical systems
  • Restrict access to trusted IP ranges only

Access Controls

  • Disable remote management features
  • Disable UPnP and unused services
  • Enforce local-only management
  • Replace shared passwords and review all configuration

Monitoring & Detection

  • Monitor HTTP traffic for requests targeting gena.cgi
  • Detect overly large SERVER_ID / HTTP_SID parameters
  • Deploy IDS/IPS signatures (Snort/Suricata) for exploitation attempts
  • Alert on unusual router behavior or unexpected reboots

Long-Term Solutions

  • Replace the DIR-816L immediately (EoL device)
  • Use modern routers with active vendor support
  • Document all affected devices and plan lifecycle upgrades
  • Ensure security patch processes exist for all network infrastructure

Technical Recommendations

Immediate Actions

  1. Identify all DIR-816L devices in your environment
  2. Verify exposure of web interface
  3. Disable remote access and UPnP
  4. Apply strict firewall rules
  5. Begin planning for device replacement

Short-Term Measures

  1. Segment router from critical networks
  2. Monitor for malicious HTTP requests
  3. Log abnormal traffic patterns
  4. Document device status and owners

Long-Term Strategy

  1. Replace DIR-816L with fully supported router models
  2. Enforce secure network architecture
  3. Train staff on IoT/network device security

Resources and References

Vulnerability Documentation

Critical Warning

This device is End-of-Life and will never receive security patches. The only secure long-term option is replacement.

Emergency Response

If compromise is suspected:

  1. Immediately disconnect the router
  2. Reset configuration to a known-good baseline
  3. Inspect network for suspicious traffic
  4. Replace the device before reconnecting