CVE-2025-11338: D-Link DI-7100G Buffer Overflow Flaw

CVE-2025-11338 Overview

A buffer overflow vulnerability has been discovered in the D-Link DI-7100G C1 router firmware up to version 20250928. This vulnerability affects the function sub_4C0990 within the file /webchat/login.cgi of the jhttpd component. Remote attackers can exploit this flaw by manipulating the openid argument, potentially leading to arbitrary code execution or system compromise on affected devices.

Critical Impact

This network-accessible buffer overflow vulnerability allows remote attackers to potentially execute arbitrary code or cause system instability on affected D-Link DI-7100G C1 routers through malicious manipulation of the openid parameter.

Affected Products

• D-Link DI-7100G C1 Firmware (up to version 2025-09-28)
• D-Link DI-7100G C1 Hardware

Discovery Timeline

• 2025-10-06 - CVE-2025-11338 published to NVD
• 2025-11-19 - Last updated in NVD database

Technical Details for CVE-2025-11338

Vulnerability Analysis

This vulnerability is classified as a buffer overflow (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw exists in the D-Link DI-7100G C1 router's web interface component, specifically within the jhttpd web server that handles HTTP requests.

The vulnerable function sub_4C0990 processes user-supplied input from the openid argument in the /webchat/login.cgi endpoint. When an attacker provides a specially crafted, oversized input value for this parameter, the function fails to properly validate the buffer boundaries, resulting in a classic buffer overflow condition.

This type of memory corruption vulnerability in embedded network devices is particularly concerning because routers often serve as network perimeters and their compromise can lead to broader network infiltration, traffic interception, or pivot attacks against internal systems.

Root Cause

The root cause of this vulnerability is improper input validation and boundary checking within the sub_4C0990 function. When processing the openid parameter from incoming HTTP requests to /webchat/login.cgi, the function does not adequately verify the length of user-supplied data before copying it into a fixed-size buffer. This allows attackers to overflow the buffer with excessive data, potentially overwriting adjacent memory regions including return addresses or function pointers.

Attack Vector

The vulnerability is exploitable remotely via network access to the router's web management interface. An attacker with low-level authentication privileges can send malicious HTTP requests to the /webchat/login.cgi endpoint with a crafted openid parameter value designed to trigger the buffer overflow. According to the vulnerability disclosure, an exploit has been published and may be actively used in attacks.

The attack can be performed without user interaction, making it suitable for automated exploitation. Network-accessible D-Link DI-7100G C1 routers with exposed management interfaces are at particular risk.

Technical details regarding the exploitation mechanism can be found in the Yuque Security Documentation and the VulDB entry #327221.

Detection Methods for CVE-2025-11338

Indicators of Compromise

• Unexpected HTTP requests to /webchat/login.cgi containing abnormally long openid parameter values
• Crash or restart events of the jhttpd service on D-Link DI-7100G C1 devices
• Unusual outbound network connections from the router suggesting potential compromise
• Memory access violation errors in device logs

Detection Strategies

• Monitor network traffic for HTTP requests to /webchat/login.cgi with openid parameters exceeding expected length thresholds
• Deploy intrusion detection system (IDS) rules to identify buffer overflow attack patterns targeting D-Link devices
• Implement web application firewall (WAF) rules to filter malicious requests to known vulnerable endpoints
• Review router logs for service crashes or unexpected restarts of the web management component

Monitoring Recommendations

• Enable comprehensive logging on D-Link DI-7100G C1 devices and forward logs to a centralized SIEM solution
• Set up alerts for multiple failed authentication attempts or unusual access patterns to the web interface
• Conduct regular vulnerability scans of network infrastructure to identify exposed management interfaces
• Monitor for any publicly released exploit tools targeting this CVE

How to Mitigate CVE-2025-11338

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management access if not required for operations
• Place affected D-Link DI-7100G C1 devices behind a firewall that filters access to management ports
• Monitor the D-Link official support page for firmware updates addressing this vulnerability

Patch Information

At the time of publication, no official patch has been released by D-Link for this vulnerability. Organizations should monitor D-Link's official security advisories and support channels for firmware updates. Given that exploits are publicly available, prioritizing mitigation measures is critical until a patch becomes available.

For additional technical details, refer to the VulDB submission #664619.

Workarounds

• Implement network segmentation to isolate affected devices from critical network assets
• Use VPN or SSH tunneling for any necessary remote access to the device management interface
• Configure access control lists (ACLs) to limit management interface access to specific trusted hosts
• Consider temporarily disabling the web management interface and using alternative management methods if available

# Example firewall rule to restrict access to router management interface
# Allow management access only from trusted admin network
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP

# Block external access to vulnerable endpoint
iptables -A INPUT -p tcp --dport 80 -i eth0 -j DROP