CVE-2026-9425: Edimax EW-7438RPn Buffer Overflow Flaw

CVE-2026-9425 Overview

CVE-2026-9425 is a stack-based buffer overflow vulnerability in the Edimax EW-7438RPn wireless range extender, firmware version 1.31. The flaw resides in the formWlanMP function within /goform/formWlanMP, where multiple HTTP request parameters are copied into fixed-size stack buffers without bounds validation. An attacker with low-privileged network access can manipulate parameters such as ateFunc, ateGain, ateRate, ateMacID, and numerous e2pTxPower fields to corrupt the stack. The exploit has been publicly disclosed and the vendor did not respond to disclosure attempts. The weakness is tracked under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Critical Impact
Remote attackers can corrupt stack memory on affected Edimax EW-7438RPn devices, potentially achieving arbitrary code execution and full device compromise.

Affected Products

Edimax EW-7438RPn firmware version 1.31
/goform/formWlanMP web management endpoint
formWlanMP function handler

Discovery Timeline

2026-05-25 - CVE-2026-9425 published to the National Vulnerability Database
2026-05-26 - Last updated in NVD database
Vendor status - Edimax was contacted prior to disclosure but did not respond

Technical Details for CVE-2026-9425

Vulnerability Analysis

The vulnerability exists in the formWlanMP handler exposed through the device's web administration interface at /goform/formWlanMP. This handler processes wireless test-mode and EEPROM configuration parameters used for radio calibration and manufacturing test functions. User-supplied values from HTTP POST or GET requests are copied directly into stack-allocated buffers without performing length checks against the destination size.

More than two dozen parameters are affected, including ateFunc, ateGain, ateTxCount, ateChan, ateRate, ateMacID, ateTxFreqOffset, ateMode, ateBW, ateAntenna, and the e2pTxPower1 through e2pTxPower7 series, plus the e2pTx2Power1 through e2pTx2Power7 series, e2pTxFreqOffset, e2pTxPwDeltaB, e2pTxPwDeltaG, e2pTxPwDeltaMix, e2pTxPwDeltaN, and readE2P. Supplying oversized values to any of these fields overwrites adjacent stack data, including the saved return address.

Root Cause

The root cause is the use of unbounded string-copy operations such as strcpy or sprintf against fixed-size stack buffers within formWlanMP. The handler trusts attacker-controlled HTTP parameter lengths and performs no validation before copying. This pattern is consistent with CWE-119, where memory operations escape the intended buffer bounds.

Attack Vector

Exploitation occurs over the network against the device's HTTP management interface. The attacker needs low-level authenticated access to submit a crafted request to /goform/formWlanMP containing an overlong value in any of the affected parameters. Successful exploitation corrupts the stack and can redirect execution to attacker-controlled shellcode, yielding code execution as the web server process — typically running as root on this class of embedded device. Refer to the GitHub Vulnerability Documentation and VulDB entry #365406 for technical proof-of-concept details.

Detection Methods for CVE-2026-9425

Indicators of Compromise

HTTP POST or GET requests to /goform/formWlanMP containing abnormally long parameter values, particularly in ateFunc, ateMacID, or any e2pTxPower* field.
Unexpected reboots, crashes, or watchdog resets of the EW-7438RPn device following inbound HTTP traffic.
Outbound connections from the range extender to unknown external hosts, indicating possible post-exploitation activity.

Detection Strategies

Inspect web server and reverse proxy logs for requests targeting /goform/formWlanMP from untrusted source addresses.
Deploy network IDS signatures that flag HTTP request bodies containing parameter values exceeding reasonable lengths for radio test fields (typically under 32 bytes).
Monitor management VLAN traffic for unauthorized access attempts to embedded device administration interfaces.

Monitoring Recommendations

Forward network telemetry from segments containing IoT and wireless infrastructure devices into a centralized analytics platform for correlation.
Alert on any HTTP request to the device's /goform/ endpoints originating from outside designated administrative subnets.
Track device firmware version inventory to identify Edimax EW-7438RPn units still running firmware 1.31.

How to Mitigate CVE-2026-9425

Immediate Actions Required

Remove the Edimax EW-7438RPn from any network segment reachable by untrusted users until a fix is available.
Block external and lateral network access to the device's HTTP management interface using firewall or VLAN ACL rules.
Change default and weak administrative credentials, since exploitation requires low-level authenticated access.
Audit existing devices for the vulnerable firmware version 1.31 and prioritize replacement of end-of-life hardware.

Patch Information

No vendor patch has been published. Edimax was contacted prior to public disclosure and did not respond. Organizations should treat the EW-7438RPn 1.31 as unsupported for this issue and plan replacement with a maintained device or alternative vendor model. Monitor the VulDB advisory for any future patch information.

Workarounds

Restrict the device's web administration interface to a dedicated management VLAN with explicit allow-listed source addresses.
Place the range extender behind a network firewall that blocks inbound HTTP and HTTPS connections from user and guest networks.
Disable remote management features if enabled, and require VPN access for any administrative session.
Replace the affected device with currently supported hardware where business requirements permit.

bash

# Example firewall rule restricting access to the device management interface
# Replace 192.0.2.10 with the device IP and 10.10.99.0/24 with the admin subnet
iptables -A FORWARD -p tcp -d 192.0.2.10 --dport 80 -s 10.10.99.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d 192.0.2.10 --dport 80 -j DROP
iptables -A FORWARD -p tcp -d 192.0.2.10 --dport 443 -s 10.10.99.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d 192.0.2.10 --dport 443 -j DROP