CVE-2025-6328: D-Link DIR-815 Buffer Overflow Vulnerability

CVE-2025-6328 Overview

CVE-2025-6328 is a stack-based buffer overflow vulnerability in the D-Link DIR-815 wireless router running firmware version 1.01. The flaw resides in the sub_403794 function within hedwig.cgi, a CGI handler exposed by the router's web management interface. Attackers can trigger the overflow remotely over the network, corrupting the call stack and potentially achieving arbitrary code execution on the device. A public proof-of-concept disclosure exists for this issue, increasing the risk to exposed devices. The vulnerability is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Critical Impact
Remote attackers with low privileges can corrupt memory in hedwig.cgi to compromise confidentiality, integrity, and availability of affected D-Link DIR-815 routers.

Affected Products

D-Link DIR-815 router (hardware revision A)
D-Link DIR-815 firmware version 1.01
Deployments exposing the router's web management interface over the network

Discovery Timeline

2025-06-20 - CVE-2025-6328 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-6328

Vulnerability Analysis

The vulnerability lives in the sub_403794 function of hedwig.cgi, a CGI binary that processes administrative HTTP requests on the DIR-815. The function fails to validate the size of attacker-controlled input before copying it into a fixed-size stack buffer. Sending an oversized request to the affected endpoint causes adjacent stack memory, including the saved return address, to be overwritten. Successful exploitation can redirect execution flow and grant the attacker control over the embedded MIPS-based device.

The D-Link DIR-815 is a legacy consumer-grade router. Devices reachable from the wide-area network or running outdated firmware on internal segments are exposed to remote compromise through this flaw.

Root Cause

The root cause is missing bounds checking on input length within sub_403794 before it is copied into a stack-allocated buffer. The handler trusts request-derived data without enforcing a maximum length, which violates safe string-handling practices in C. This is a classic stack-based buffer overflow pattern frequently seen in embedded CGI binaries that use unsafe routines such as strcpy or sprintf.

Attack Vector

The attack vector is network-based and requires low privileges, with no user interaction. An attacker sends a crafted HTTP request to the hedwig.cgi endpoint of the router's web interface. The malformed parameter triggers the overflow in sub_403794, overwriting stack frames. A reliable exploit allows code execution under the privileges of the web service, typically root on this class of device. Technical details and a proof-of-concept are referenced in the GitHub CVE PoC Repository and VulDB entry #313324.

Detection Methods for CVE-2025-6328

Indicators of Compromise

Unexpected HTTP POST or GET requests targeting hedwig.cgi with abnormally long parameter values
Unexplained reboots, service crashes, or watchdog resets on the DIR-815 router
New outbound connections from the router to unknown hosts, indicating possible implant deployment
Changes to DNS, DHCP, or firewall configuration that were not made by an administrator

Detection Strategies

Inspect web server and CGI logs on the router (where available) for requests to hedwig.cgi containing oversized fields
Deploy network IDS/IPS signatures that flag HTTP requests exceeding expected parameter lengths to embedded device management URIs
Baseline normal management traffic for the DIR-815 and alert on deviations in request size, frequency, or source address

Monitoring Recommendations

Monitor egress traffic from the router's IP address for connections to threat-intelligence-tagged infrastructure
Track administrative interface exposure on perimeter scans and alert when port 80 or 443 of consumer routers becomes reachable from the internet
Correlate router behavior anomalies with EPSS trends; the current EPSS score is approximately 0.81%

How to Mitigate CVE-2025-6328

Immediate Actions Required

Restrict access to the router's web management interface to trusted internal hosts only, and never expose it to the internet
Disable remote administration features on the DIR-815 if they are enabled
Place legacy D-Link DIR-815 devices behind a segmented network with strict egress filtering
Plan replacement of end-of-life DIR-815 hardware with currently supported models, as vendor patches for this firmware are unlikely

Patch Information

No vendor advisory or patched firmware release has been associated with CVE-2025-6328 at the time of publication. The DIR-815 is a legacy product line, and updates may not be issued. Check the D-Link Official Website for product status and any subsequent security bulletins.

Workarounds

Block external access to TCP ports 80 and 443 on the router at the upstream firewall
Use an ACL on the router to limit management access to a single trusted management workstation
Disable UPnP and any WAN-side services that are not strictly required
Replace the affected device with a supported router that receives active security updates

bash

# Example upstream firewall rule to block WAN access to the router's web UI
# Replace <ROUTER_WAN_IP> with the affected device's WAN address
iptables -A FORWARD -d <ROUTER_WAN_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_WAN_IP> -p tcp --dport 443 -j DROP