CVE-2026-9403 Overview
CVE-2026-9403 is a buffer overflow vulnerability in the Edimax BR-6675nD wireless router, firmware version 1.12. The flaw resides in the formWlSiteSurvey function within /goform/formWlSiteSurvey, part of the device's POST request handler. Attackers can manipulate the selSSID argument to overflow a memory buffer and corrupt adjacent memory. The issue is classified under [CWE-119] (improper restriction of operations within the bounds of a memory buffer). The exploit has been publicly disclosed. According to the disclosure, the vendor was contacted but did not respond.
Critical Impact
Remote attackers with low privileges can trigger memory corruption in the router's web management interface, potentially leading to arbitrary code execution or denial of service on the affected device.
Affected Products
- Edimax BR-6675nD wireless router
- Firmware version 1.12
- /goform/formWlSiteSurvey POST request handler component
Discovery Timeline
- 2026-05-24 - CVE-2026-9403 published to NVD
- 2026-05-26 - Last updated in NVD database
Technical Details for CVE-2026-9403
Vulnerability Analysis
The vulnerability affects the formWlSiteSurvey handler exposed by the router's HTTP management interface at /goform/formWlSiteSurvey. This endpoint processes wireless site survey requests submitted via HTTP POST. The handler reads the selSSID parameter from the request body and copies it into a fixed-size stack or heap buffer without enforcing a length check. An attacker who supplies an oversized selSSID value can write past the buffer boundary and overwrite adjacent memory structures.
Memory corruption in an embedded MIPS or ARM web server typically allows control over saved return addresses or function pointers. Exploitation can lead to arbitrary code execution in the context of the web management daemon, which generally runs with root privileges on consumer routers.
Root Cause
The root cause is a missing bounds check on user-supplied input. The formWlSiteSurvey function trusts the length of the selSSID POST parameter and uses an unsafe copy operation, such as strcpy or sprintf, into a fixed-size buffer. This pattern, categorized as [CWE-119], is recurrent in legacy embedded firmware where input validation is delegated to the front-end and not enforced server-side.
Attack Vector
The attack is initiated over the network against the router's HTTP management interface. The attacker submits a crafted POST request to /goform/formWlSiteSurvey with an oversized selSSID value. Authentication with low privileges is required, as reflected in the CVSS vector. Exploitation against management interfaces exposed to the LAN is straightforward, and exposure to the WAN side increases risk significantly.
The vulnerability mechanism is documented in the public disclosure. See the Notion Site Survey Document and the VulDB Vulnerability Detail for technical context.
Detection Methods for CVE-2026-9403
Indicators of Compromise
- HTTP POST requests to /goform/formWlSiteSurvey containing an unusually long selSSID parameter value
- Unexpected reboots, crashes, or restarts of the router's web management daemon
- Outbound connections from the router to unknown hosts following suspicious management traffic
- Configuration changes to the device not initiated by an authorized administrator
Detection Strategies
- Inspect HTTP request bodies destined for the router's management interface and flag selSSID values exceeding expected SSID length limits (32 bytes per IEEE 802.11)
- Deploy network intrusion detection signatures matching POST requests to /goform/formWlSiteSurvey with oversized parameters
- Correlate authentication events on the router with subsequent management traffic to identify low-privileged accounts triggering crashes
Monitoring Recommendations
- Log and review all administrative access to consumer-grade routers, especially from non-management VLANs
- Monitor SNMP or syslog output from the affected devices for daemon restarts or watchdog resets
- Track DNS and outbound flow telemetry from router IP addresses to detect post-exploitation activity
How to Mitigate CVE-2026-9403
Immediate Actions Required
- Restrict access to the router's web management interface to trusted management subnets only; disable WAN-side administration
- Change default and weak credentials on the device to limit who can authenticate and reach the vulnerable handler
- Isolate the BR-6675nD on a segmented network until a firmware fix or replacement is available
- Consider replacing the device, as the BR-6675nD is a legacy product and the vendor did not respond to the disclosure
Patch Information
At the time of publication, no vendor patch is available. The disclosure record indicates that Edimax was contacted prior to publication but did not respond. Consult the VulDB CTI Analysis on Vulnerability and the VulDB Vulnerability Submission for any updates on vendor response or firmware availability.
Workarounds
- Block external access to TCP ports serving the router's HTTP administration interface using upstream firewall rules
- Disable remote management features and limit administration to wired connections from a dedicated management host
- Place the affected device behind a reverse proxy or filtering appliance that enforces parameter length limits on requests to /goform/formWlSiteSurvey
- Plan migration to a supported router model with an active security maintenance program
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
