CVE-2026-7684: Edimax BR-6428nC Buffer Overflow Flaw

CVE-2026-7684 Overview

CVE-2026-7684 is a stack-based buffer overflow in the Edimax BR-6428nC wireless router, affecting versions up to 1.16. The flaw resides in an unspecified handler within the /goform/setWAN endpoint, where the pptpDfGateway parameter is processed without proper bounds checking. An authenticated remote attacker can submit an oversized value to corrupt stack memory and trigger the overflow [CWE-119]. Public disclosure includes a technical write-up and VulDB submission, and the vendor did not respond to coordinated disclosure attempts. The exploit details have been disclosed publicly and may be used by attackers.

Critical Impact

Remote attackers with low privileges can trigger a stack buffer overflow over the network, potentially leading to denial of service or arbitrary code execution on the affected router.

Affected Products

• Edimax BR-6428nC wireless router
• Firmware versions up to and including 1.16
• Devices exposing the /goform/setWAN web management endpoint

Discovery Timeline

• 2026-05-03 - CVE-2026-7684 published to NVD
• 2026-05-05 - Last updated in NVD database

Technical Details for CVE-2026-7684

Vulnerability Analysis

The vulnerability exists in the HTTP request handler bound to /goform/setWAN, which processes WAN configuration parameters submitted through the router's web interface. When the handler reads the pptpDfGateway argument from the user-supplied form data, it copies the value into a fixed-size stack buffer without validating the input length. Supplying a string larger than the destination buffer overwrites adjacent stack memory, including saved registers and the return address.

Because embedded MIPS or ARM-based SoC firmware on consumer routers typically lacks modern exploit mitigations such as stack canaries, ASLR, and non-executable stacks, return-address corruption can be converted into arbitrary code execution. At minimum, the corruption crashes the HTTP daemon (goahead or boa style server) and renders the device inoperable until rebooted.

Root Cause

The root cause is missing bounds validation on the pptpDfGateway POST parameter before it is copied into a stack-allocated buffer, classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). The handler trusts attacker-controlled length without enforcing a maximum size or using a length-limited copy primitive such as strncpy with a correct size argument.

Attack Vector

Exploitation requires network access to the router's management interface and low-level authenticated session credentials. The attacker sends a crafted HTTP POST request to /goform/setWAN containing an overlong pptpDfGateway value. No user interaction is required beyond sending the request. Where the management interface is exposed to the WAN side, the vulnerability is reachable from the public internet. Refer to the Notion Stack Overflow Report and VulDB Vulnerability #360843 for the technical proof-of-concept details.

Detection Methods for CVE-2026-7684

Indicators of Compromise

• HTTP POST requests to /goform/setWAN containing unusually long pptpDfGateway parameter values, typically exceeding 100 bytes
• Unexpected restarts or crashes of the router's httpd web management process visible in syslog output
• Unauthorized changes to WAN PPTP configuration or new outbound connections originating from the router itself

Detection Strategies

• Inspect web server access logs on the device or upstream proxy for POST requests to /goform/setWAN with abnormal payload sizes
• Deploy network IDS signatures matching long pptpDfGateway strings in HTTP request bodies destined for Edimax management ports
• Correlate router reboot events with preceding HTTP requests to administrative goform endpoints

Monitoring Recommendations

• Forward router syslog and authentication events to a centralized log platform for anomaly review
• Alert on any external source IP attempting to reach the router's management interface on TCP/80 or TCP/443
• Track repeated authentication attempts against the Edimax web interface that precede setWAN requests

How to Mitigate CVE-2026-7684

Immediate Actions Required

• Disable remote WAN-side access to the router's web management interface and restrict administration to trusted LAN hosts only
• Change default and weak administrator credentials, since exploitation requires an authenticated session
• Place the affected device behind a network segmentation boundary that blocks untrusted access to /goform/setWAN

Patch Information

No vendor patch is available at the time of publication. The vendor was contacted prior to disclosure but did not respond. Organizations operating the Edimax BR-6428nC at firmware version 1.16 or earlier should treat the device as unpatched and consider replacement with a supported router model. Monitor the VulDB advisory for any future vendor response.

Workarounds

• Block inbound connections to the router's HTTP and HTTPS management ports from all untrusted networks using upstream firewall rules
• Disable the PPTP WAN configuration feature if the device supports alternate WAN modes that do not invoke the vulnerable code path
• Replace end-of-support consumer routers with current-generation hardware that receives active firmware updates

# Example upstream firewall rule to block external access to the router admin UI
iptables -A FORWARD -p tcp -d <router-ip> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <router-ip> --dport 443 -j DROP