CVE-2025-8159: D-Link DIR-513 Buffer Overflow Vulnerability

CVE-2025-8159 Overview

A critical stack-based buffer overflow vulnerability has been identified in the D-Link DIR-513 router firmware version 1.0. The vulnerability exists in the formLanguageChange function within the HTTP POST Request Handler component, specifically in the file /goform/formLanguageChange. By manipulating the curTime argument, a remote attacker can trigger a stack-based buffer overflow, potentially leading to arbitrary code execution or denial of service on the affected device.

Critical Impact

This vulnerability allows remote attackers to exploit a stack-based buffer overflow in end-of-life D-Link DIR-513 routers, potentially achieving full device compromise through network-based attacks without complex prerequisites.

Affected Products

• D-Link DIR-513 Firmware version 1.0
• D-Link DIR-513 Hardware (End-of-Life product)

Discovery Timeline

• 2025-07-25 - CVE-2025-8159 published to NVD
• 2025-09-16 - Last updated in NVD database

Technical Details for CVE-2025-8159

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-787: Out-of-bounds Write, CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the formLanguageChange function, which handles HTTP POST requests for language configuration changes on the router's web interface. When processing the curTime parameter, the function fails to properly validate the input length before copying data to a fixed-size stack buffer, allowing an attacker to overflow the buffer and overwrite adjacent memory on the stack.

The vulnerability is particularly concerning because the affected D-Link DIR-513 router is an end-of-life product that will not receive security patches from the vendor. This leaves all deployed devices permanently vulnerable to exploitation.

Root Cause

The root cause of CVE-2025-8159 is insufficient bounds checking in the formLanguageChange function when handling user-supplied input through the curTime parameter. The function allocates a fixed-size buffer on the stack and copies the incoming parameter value without verifying that the input length does not exceed the buffer capacity. This classic buffer overflow pattern allows attackers to write beyond the allocated buffer boundaries, corrupting the stack and potentially hijacking program execution flow.

Attack Vector

The attack can be initiated remotely over the network by sending a specially crafted HTTP POST request to the /goform/formLanguageChange endpoint on the router's web interface. An attacker with low-level privileges (such as authenticated access to the router's web interface) can exploit this vulnerability by providing an oversized value for the curTime parameter. The attack does not require user interaction and can be executed with low complexity.

A successful exploitation could allow the attacker to:

• Execute arbitrary code on the router with elevated privileges
• Cause a denial of service by crashing the device
• Potentially gain persistent access to the network infrastructure

For detailed technical analysis of the exploitation mechanism, refer to the vulnerability disclosure document on GitHub.

Detection Methods for CVE-2025-8159

Indicators of Compromise

• Unusual HTTP POST requests to /goform/formLanguageChange with abnormally long curTime parameter values
• Router crashes, unexpected reboots, or unresponsive web management interface
• Anomalous outbound network traffic from the router indicating potential compromise
• Unexpected changes to router configuration or firmware

Detection Strategies

• Implement network-based intrusion detection rules to monitor HTTP POST requests to D-Link router endpoints containing oversized parameters
• Deploy network traffic analysis to identify buffer overflow attack patterns targeting /goform/formLanguageChange
• Configure web application firewalls to block requests with excessively long parameter values to router management interfaces
• Monitor for known exploitation signatures referenced in VulDB CTI Indicator #317573

Monitoring Recommendations

• Enable logging on network firewalls to capture all traffic directed at D-Link router management ports (typically ports 80/443)
• Implement network segmentation to isolate vulnerable IoT devices and monitor cross-segment traffic
• Deploy endpoint detection solutions capable of monitoring embedded device behavior anomalies
• Regularly review router access logs for suspicious authentication attempts or management interface access

How to Mitigate CVE-2025-8159

Immediate Actions Required

• Immediately restrict network access to the router's web management interface by disabling remote management
• Implement firewall rules to block external access to the router's administration ports
• Isolate affected D-Link DIR-513 devices on a separate network segment with strict access controls
• Plan for device replacement as the DIR-513 is end-of-life and will not receive vendor patches

Patch Information

No patch is available for CVE-2025-8159. The D-Link DIR-513 router has reached end-of-life status and is no longer supported by the manufacturer. D-Link has not released and will not release a security update for this vulnerability. Organizations using affected devices should prioritize replacement with currently supported router models. For more information, visit the D-Link official website.

Workarounds

• Disable the web-based management interface entirely if not required for operations
• Restrict management interface access to trusted internal IP addresses only using ACLs
• Place the router behind a firewall that blocks all inbound traffic to the management interface
• Consider deploying a third-party firewall or IPS solution to filter malicious requests targeting the vulnerable endpoint
• Replace the end-of-life D-Link DIR-513 with a supported router model that receives security updates

# Example: Block external access to router management interface
# Add firewall rules to restrict access to router admin ports
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP