CVE-2025-70240: D-Link DIR-513 Buffer Overflow Flaw

CVE-2025-70240 Overview

A stack buffer overflow vulnerability has been identified in D-Link DIR-513 router firmware version 1.10. The vulnerability exists in the goform/formSetWAN_Wizard51 endpoint, where the curTime parameter is improperly handled, allowing attackers to overflow a stack-based buffer. This firmware vulnerability in consumer networking equipment represents a significant security risk as it can be exploited remotely without authentication.

Critical Impact

This stack buffer overflow vulnerability allows remote attackers to potentially execute arbitrary code or cause denial of service on affected D-Link DIR-513 routers without requiring authentication, putting home and small business networks at risk.

Affected Products

• D-Link DIR-513 Firmware version 1.10
• D-Link DIR-513 Hardware (all revisions running vulnerable firmware)

Discovery Timeline

• 2026-03-03 - CVE-2025-70240 published to NVD
• 2026-03-04 - Last updated in NVD database

Technical Details for CVE-2025-70240

Vulnerability Analysis

This vulnerability is classified under CWE-787 (Out-of-bounds Write), a category of memory corruption vulnerabilities where data is written past the boundaries of allocated memory. In the context of this D-Link router firmware, the vulnerability manifests when user-supplied input via the curTime parameter is copied to a fixed-size stack buffer without proper length validation.

The attack can be performed remotely over the network and requires no authentication or user interaction. Successful exploitation could allow an attacker to overwrite adjacent stack memory, including return addresses and saved registers, potentially leading to arbitrary code execution with the privileges of the web server process running on the router. Given that embedded devices often run services with elevated privileges, this could result in complete device compromise.

Root Cause

The root cause of this vulnerability is inadequate input validation and improper bounds checking when processing the curTime parameter in the formSetWAN_Wizard51 form handler. The firmware fails to verify that the length of user-supplied data fits within the allocated stack buffer before performing the copy operation. This is a common vulnerability pattern in embedded device firmware where memory-safe programming practices are not consistently applied to HTTP form handlers.

Attack Vector

The vulnerability is exploited through the network by sending a specially crafted HTTP request to the goform/formSetWAN_Wizard51 endpoint on the router's web management interface. The attack vector involves:

1. Identifying a vulnerable D-Link DIR-513 router on the network
2. Crafting an HTTP POST request to the /goform/formSetWAN_Wizard51 endpoint
3. Including an oversized curTime parameter value designed to overflow the stack buffer
4. The overflow can overwrite the return address on the stack, redirecting execution flow

The vulnerability is accessible without authentication, meaning any attacker who can reach the router's management interface can attempt exploitation. For detailed technical analysis, refer to the GitHub CVE Report.

Detection Methods for CVE-2025-70240

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/formSetWAN_Wizard51 containing abnormally long curTime parameter values
• Router crashes, reboots, or unresponsive behavior following web interface access
• Unusual outbound network connections originating from the router
• Modified router configuration or unauthorized administrative access

Detection Strategies

• Monitor network traffic for HTTP requests to D-Link router management interfaces with anomalous payload sizes
• Implement intrusion detection rules to flag requests containing oversized parameters to known vulnerable endpoints
• Deploy network segmentation to isolate IoT and network devices from untrusted network segments
• Regularly audit firmware versions on network infrastructure devices to identify vulnerable installations

Monitoring Recommendations

• Enable logging on network firewalls and IDS/IPS systems to capture traffic to router management interfaces
• Set up alerts for any external access attempts to router administrative endpoints
• Monitor for unusual patterns of router restarts or service interruptions
• Consider deploying a dedicated IoT security monitoring solution for network devices

How to Mitigate CVE-2025-70240

Immediate Actions Required

• Disable remote management access on affected D-Link DIR-513 routers immediately
• Restrict access to the router's web management interface to trusted internal networks only
• Check the D-Link Security Bulletin for firmware updates addressing this vulnerability
• Consider replacing end-of-life devices that no longer receive security updates
• Implement network segmentation to limit exposure of vulnerable devices

Patch Information

At the time of publication, organizations should monitor the D-Link Security Bulletin for official patches or firmware updates. Given that the DIR-513 is an older product line, it may have reached end-of-life status and may not receive security updates. Users should verify the support status of their device through the D-Link Product Information page and consider replacement if the device is no longer supported.

Workarounds

• Disable the web management interface entirely if not required for operations
• Configure firewall rules to block external access to the router's management ports (typically port 80/443)
• Place the router behind a separate firewall that can filter malicious requests
• Use VPN for any required remote management access rather than exposing the interface directly
• Schedule device replacement if running end-of-life hardware without available patches

# Example firewall rule to restrict management interface access (iptables)
# Block external access to router management interface
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP