CVE-2026-9427 Overview
CVE-2026-9427 is a stack-based buffer overflow in the Edimax EW-7438RPn wireless range extender, firmware version 1.31. The flaw resides in the formWlSiteSurvey function inside /goform/formWlSiteSurvey, part of the webs web management component. Attackers manipulate the selSSID and submit-url arguments to overflow a fixed-size stack buffer. The exploit has been published, and the vendor did not respond to disclosure attempts. The issue is tracked under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).
Critical Impact
Remote authenticated attackers can corrupt the stack of the embedded web server and potentially execute arbitrary code on the device, gaining full control of the wireless extender.
Affected Products
- Edimax EW-7438RPn firmware version 1.31
- The webs HTTP management daemon
- The /goform/formWlSiteSurvey endpoint (function formWlSiteSurvey)
Discovery Timeline
- 2026-05-25 - CVE-2026-9427 published to NVD
- 2026-05-26 - Last updated in NVD database
Technical Details for CVE-2026-9427
Vulnerability Analysis
The vulnerability exists in the wireless site survey handler of the Edimax EW-7438RPn web administration interface. The formWlSiteSurvey function processes HTTP POST requests to /goform/formWlSiteSurvey and copies user-supplied data from the selSSID and submit-url parameters into fixed-size stack buffers without bounds checking. Sending an oversized value for either parameter overruns the destination buffer and overwrites adjacent stack memory, including the saved return address.
Because the webs daemon runs with elevated privileges on the embedded device, successful exploitation yields full administrative control of the range extender. The vendor did not respond to disclosure, and no official patch exists. Exploit proof-of-concept material is publicly available through the GitHub vulnerability document and VulDB entry #365408.
Root Cause
The root cause is missing length validation on the selSSID and submit-url request parameters before they are copied into stack-allocated buffers in formWlSiteSurvey. Embedded web handlers in the webs binary rely on unsafe string operations rather than length-bounded equivalents, classifying the issue under [CWE-119].
Attack Vector
An attacker reaches the vulnerable endpoint over the network by sending a crafted HTTP request to the device's management interface. The request requires low-privilege authentication to the web UI. Once the malformed parameters are processed, the stack corruption disrupts control flow and can be steered toward arbitrary code execution on the MIPS-class embedded processor.
No verified exploit code is included here. Refer to the published proof-of-concept for technical reproduction details.
Detection Methods for CVE-2026-9427
Indicators of Compromise
- HTTP POST requests to /goform/formWlSiteSurvey containing abnormally long selSSID or submit-url values
- Unexpected reboots or crashes of the webs process on the EW-7438RPn
- Outbound connections from the device to unfamiliar IP addresses following management-interface traffic
Detection Strategies
- Inspect web server and router logs for formWlSiteSurvey requests with parameter lengths exceeding typical SSID sizes (32 bytes) or normal URL lengths.
- Deploy network IDS signatures that match POST bodies to /goform/formWlSiteSurvey containing oversized selSSID= or submit-url= values.
- Correlate authentication events with subsequent crashes of the management daemon to surface exploitation attempts.
Monitoring Recommendations
- Restrict and monitor access to the device administrative interface from segmented management VLANs only.
- Capture and review HTTP traffic to all /goform/ endpoints on Edimax devices for anomalous payload sizes.
- Alert on repeated authentication failures followed by successful logins to the EW-7438RPn web UI.
How to Mitigate CVE-2026-9427
Immediate Actions Required
- Remove the EW-7438RPn from untrusted network segments and block external access to its web management interface.
- Change the default administrative password and enforce strong credentials, since exploitation requires authenticated access.
- Disable remote management features if not strictly needed for operations.
Patch Information
No vendor patch is available. The vendor was contacted ahead of disclosure but did not respond. Organizations relying on the EW-7438RPn 1.31 should plan device replacement with a supported wireless extender that receives security updates.
Workarounds
- Place affected devices behind a firewall that blocks inbound HTTP/HTTPS to the management interface.
- Restrict management access to a dedicated administrator workstation via ACLs on the upstream switch or router.
- Monitor for and rate-limit requests to /goform/formWlSiteSurvey at the network layer until devices are retired.
# Example: block external access to the EW-7438RPn management UI using iptables on an upstream gateway
iptables -A FORWARD -d <EW-7438RPn-IP> -p tcp --dport 80 -m iprange ! --src-range 10.0.0.10-10.0.0.20 -j DROP
iptables -A FORWARD -d <EW-7438RPn-IP> -p tcp --dport 443 -m iprange ! --src-range 10.0.0.10-10.0.0.20 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
