CVE-2026-9294 Overview
CVE-2026-9294 is a buffer overflow vulnerability in the Edimax BR-6428NS router running firmware version 1.10. The flaw resides in the formWanTcpipSetup function within /goform/formWanTcpipSetup, which handles POST requests for WAN TCP/IP configuration. Attackers can trigger the overflow by manipulating the pppUserName argument. The vulnerability is exploitable remotely over the network and a public exploit is available. According to the disclosure, the vendor was contacted but did not respond. The weakness is categorized under CWE-119, improper restriction of operations within the bounds of a memory buffer.
Critical Impact
Remote attackers with low privileges can corrupt router memory through the pppUserName POST parameter, potentially achieving arbitrary code execution on the device.
Affected Products
- Edimax BR-6428NS firmware version 1.10
- Component: POST Request Handler (/goform/formWanTcpipSetup)
- Affected function: formWanTcpipSetup
Discovery Timeline
- 2026-05-23 - CVE-2026-9294 published to the National Vulnerability Database
- 2026-05-26 - Last updated in NVD database
Technical Details for CVE-2026-9294
Vulnerability Analysis
The Edimax BR-6428NS exposes a web-based administration interface that processes WAN configuration through the formWanTcpipSetup handler. When a client submits a POST request to /goform/formWanTcpipSetup, the handler reads the pppUserName argument used for PPPoE authentication credentials. The handler copies this user-controlled string into a fixed-size buffer without validating its length, producing a classic stack or heap buffer overflow [CWE-119].
An attacker on the network with valid low-privilege credentials can supply an oversized pppUserName value to overwrite adjacent memory. Depending on the surrounding memory layout and the absence of exploit mitigations on embedded MIPS or ARM SoHo routers, the overflow can crash the device, alter control data, or redirect execution to attacker-supplied code. The exploit is publicly disclosed, increasing the likelihood of opportunistic abuse against exposed devices.
Root Cause
The root cause is missing bounds checking on the pppUserName POST parameter before it is copied into a fixed-length buffer inside the formWanTcpipSetup function. The handler trusts the request length supplied by the client and performs an unsafe copy operation typical of strcpy or sprintf patterns common in legacy embedded web servers.
Attack Vector
Exploitation requires network access to the router's HTTP management interface and authenticated access at a low privilege level. The attacker sends a crafted POST request to /goform/formWanTcpipSetup with an overlong pppUserName field. No user interaction is required. Devices exposing their management interface to the WAN or to broad LAN segments face the highest exposure.
No verified exploit code is available in this advisory. Refer to the VulDB entry #365241 and the public technical writeup for additional technical detail.
Detection Methods for CVE-2026-9294
Indicators of Compromise
- POST requests to /goform/formWanTcpipSetup containing unusually long pppUserName values, particularly exceeding typical PPPoE username lengths of 64 to 128 characters.
- Unexpected reboots, crashes, or watchdog resets on Edimax BR-6428NS devices following inbound HTTP traffic.
- Configuration changes to WAN settings that do not correspond to legitimate administrator activity.
Detection Strategies
- Inspect HTTP request bodies destined for the router management interface and flag POST parameters that exceed expected length boundaries.
- Correlate router log entries showing failed authentication followed by successful low-privilege logins and subsequent WAN configuration POSTs.
- Monitor for outbound connections initiated by the router to unfamiliar hosts, which may indicate post-exploitation activity.
Monitoring Recommendations
- Forward router syslog and web server access logs to a centralized log platform for retention and anomaly analysis.
- Establish a baseline of administrative POST activity to /goform/ endpoints and alert on deviations.
- Periodically scan the network for Edimax BR-6428NS devices and verify firmware versions against the latest available release.
How to Mitigate CVE-2026-9294
Immediate Actions Required
- Restrict access to the router's HTTP management interface to trusted management VLANs only, and disable WAN-side administration.
- Rotate administrative credentials and disable any unused low-privilege accounts that could be leveraged to reach the vulnerable handler.
- Place the affected device behind a network segment that filters POST requests to /goform/formWanTcpipSetup from untrusted sources.
- Plan replacement of the BR-6428NS with a supported device, as the vendor did not respond to the disclosure.
Patch Information
No vendor patch is available. According to the disclosure record on VulDB #365241, Edimax was contacted but did not respond. Until a firmware update is released, treat the device as unpatched and apply compensating network controls. Monitor the Edimax support portal for any future firmware advisories addressing the formWanTcpipSetup handler.
Workarounds
- Disable the router's remote management feature and block inbound HTTP and HTTPS traffic to the device from the WAN interface at the upstream firewall.
- Apply an ACL or web application firewall rule that limits the size of POST parameters submitted to /goform/formWanTcpipSetup, dropping requests with pppUserName values exceeding a conservative length.
- Isolate the router on a dedicated VLAN and restrict management access to a single hardened administrative host.
# Example upstream firewall rule (iptables) blocking WAN access to router HTTP admin
iptables -A FORWARD -p tcp -d <router-ip> --dport 80 -i <wan-iface> -j DROP
iptables -A FORWARD -p tcp -d <router-ip> --dport 443 -i <wan-iface> -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
