CVE-2026-9461: Edimax EW-7438RPn Buffer Overflow Flaw

CVE-2026-9461 Overview

CVE-2026-9461 is a stack-based buffer overflow [CWE-119] in the Edimax EW-7438RPn wireless range extender running firmware version 1.31. The flaw resides in the formRadius function within /goform/formRadius, where the submit-url argument is copied without proper bounds checking. Remote attackers with low privileges can trigger memory corruption over the network, leading to denial of service or arbitrary code execution on the device. The exploit has been publicly disclosed, and the vendor did not respond to the disclosure attempt, leaving deployed devices without an official fix.

Critical Impact

Remote attackers can corrupt stack memory through the submit-url parameter, potentially gaining code execution on affected Edimax EW-7438RPn devices.

Affected Products

• Edimax EW-7438RPn firmware version 1.31
• The formRadius handler in /goform/formRadius
• The submit-url parameter processing routine

Discovery Timeline

• 2026-05-25 - CVE-2026-9461 published to NVD
• 2026-05-26 - Last updated in NVD database

Technical Details for CVE-2026-9461

Vulnerability Analysis

The vulnerability resides in the formRadius function exposed through the device's web management interface at /goform/formRadius. When a request is submitted, the handler reads the submit-url parameter and copies it into a fixed-size stack buffer without validating its length. An attacker who sends an oversized value overwrites adjacent stack memory, including saved registers and the return address.

The handler runs as part of the embedded HTTP server on the range extender. Successful exploitation can crash the device or redirect execution flow to attacker-controlled data. Because embedded MIPS/ARM firmware of this class typically lacks Address Space Layout Randomization (ASLR) and stack canaries, return address overwrites translate directly into reliable code execution primitives.

Root Cause

The root cause is missing length validation on user-supplied input before invoking an unsafe string copy into a stack-allocated buffer. The submit-url argument is treated as a trusted, fixed-length value when in practice the HTTP request body is fully attacker-controlled.

Attack Vector

Exploitation requires network reachability to the device's web interface and a valid low-privilege session, consistent with the CVSS vector indicating low privileges required and no user interaction. An attacker submits a crafted POST request to /goform/formRadius with an oversized submit-url field. The malformed input overflows the stack buffer, corrupting control data. Public proof-of-concept details are referenced in the GitHub Vulnerability Report and VulDB entry #365442.

Detection Methods for CVE-2026-9461

Indicators of Compromise

• HTTP POST requests to /goform/formRadius containing abnormally long submit-url parameter values, typically exceeding several hundred bytes.
• Unexpected reboots, watchdog resets, or HTTP service crashes on Edimax EW-7438RPn devices.
• Outbound connections from the extender to unfamiliar hosts following suspicious formRadius requests.

Detection Strategies

• Inspect web server access logs for requests targeting /goform/formRadius with payload sizes inconsistent with normal administrative use.
• Deploy network intrusion detection signatures that flag oversized form parameters destined for embedded device management interfaces on the LAN.
• Correlate device availability events with preceding HTTP traffic to detect crash-restart cycles indicative of exploitation attempts.

Monitoring Recommendations

• Continuously monitor management VLAN traffic to consumer-grade network appliances for anomalous HTTP body lengths.
• Alert on authentication events against the EW-7438RPn followed by formRadius POST requests within short time windows.
• Track firmware version inventory to identify devices running version 1.31 that remain exposed.

How to Mitigate CVE-2026-9461

Immediate Actions Required

• Remove the Edimax EW-7438RPn web management interface from any untrusted network segment and restrict access to a dedicated administrative VLAN.
• Change default and reused administrative credentials, since exploitation requires an authenticated session.
• Audit existing deployments and consider replacing the device given the vendor's lack of response to disclosure.

Patch Information

No vendor patch is available. According to the disclosure, Edimax was contacted prior to public release but did not respond. Organizations should assume the vulnerability will remain unfixed in firmware 1.31 and plan compensating controls or device replacement accordingly.

Workarounds

• Disable remote management on the WAN interface and limit web administration to wired LAN clients only.
• Place affected devices behind a firewall that blocks inbound HTTP requests to /goform/formRadius from unauthorized sources.
• Segment IoT and network infrastructure devices away from user workstations to limit lateral movement following compromise.

# Example firewall rule restricting access to the device management interface
iptables -A FORWARD -p tcp -d <extender_ip> --dport 80 \
  -m iprange ! --src-range 10.0.10.10-10.0.10.20 -j DROP