CVE-2026-9426 Overview
CVE-2026-9426 is a stack-based buffer overflow [CWE-119] in the Edimax EW-7438RPn wireless range extender, firmware version 1.31. The vulnerability resides in the formHwSet function within /goform/formHwSet. Attackers can manipulate multiple parameters including Anntena, Mcs, regDomain, nic0Addr, nic1Addr, wlanAddr, wanAddr, wlanSSID, wlanChan, initgain, txcck, txofdm, and submit-url to trigger memory corruption. The exploit is publicly available. The vendor was contacted prior to disclosure but did not respond.
Critical Impact
Authenticated remote attackers can corrupt memory on affected Edimax EW-7438RPn devices, enabling potential code execution and full device compromise.
Affected Products
- Edimax EW-7438RPn firmware version 1.31
- /goform/formHwSet HTTP handler
- formHwSet function within the device web management interface
Discovery Timeline
- 2026-05-25 - CVE-2026-9426 published to NVD
- 2026-05-26 - Last updated in NVD database
Technical Details for CVE-2026-9426
Vulnerability Analysis
The flaw exists in the formHwSet request handler exposed at /goform/formHwSet on the Edimax EW-7438RPn web administration interface. The handler accepts numerous user-controlled parameters used to configure hardware-level wireless settings. These values are copied into fixed-size stack buffers without proper length validation, producing a classic stack-based buffer overflow condition.
Because the overflow occurs on the stack, attackers can overwrite saved return addresses or adjacent control structures. On MIPS-based embedded devices like the EW-7438RPn, this typically enables return-oriented attacks against the device firmware. The vulnerability is reachable over the network and requires low-privilege authentication. See the GitHub Vulnerability Documentation for parameter-level details.
Root Cause
The root cause is missing bounds checking on parameters processed by formHwSet. The handler trusts client-supplied strings for fields such as wlanSSID, nic0Addr, wanAddr, and submit-url, then writes them into stack buffers with unsafe string operations. No length validation, truncation, or canary enforcement prevents the overflow.
Attack Vector
An attacker with access to the device management interface sends a crafted HTTP POST request to /goform/formHwSet containing oversized values for any of the vulnerable arguments. Successful exploitation corrupts the stack frame of formHwSet, leading to a crash or arbitrary code execution within the web server process. The exploit has been publicly disclosed in the referenced VulDB entry #365407, increasing the likelihood of opportunistic use against exposed devices.
No verified proof-of-concept code is reproduced here. The vulnerability mechanism follows the standard pattern of unbounded strcpy-style copies of HTTP form values into stack-allocated buffers within the formHwSet handler.
Detection Methods for CVE-2026-9426
Indicators of Compromise
- HTTP POST requests to /goform/formHwSet containing abnormally long values for wlanSSID, nic0Addr, nic1Addr, wanAddr, wlanAddr, regDomain, or submit-url
- Unexpected reboots, crashes, or httpd process restarts on EW-7438RPn devices
- Outbound connections from the range extender to unfamiliar hosts after configuration requests
Detection Strategies
- Inspect web traffic destined for EW-7438RPn management interfaces and alert on parameter lengths that exceed typical configuration values
- Apply IDS signatures matching long ASCII or shellcode-like payloads in formHwSet POST bodies
- Correlate device crash logs and SNMP availability dips with administrative HTTP requests
Monitoring Recommendations
- Forward router and access point logs to a centralized log platform for parameter and session anomaly review
- Monitor for any exposure of EW-7438RPn management interfaces to untrusted network segments or the internet
- Track authentication events to the device and alert on configuration changes from unexpected source addresses
How to Mitigate CVE-2026-9426
Immediate Actions Required
- Restrict access to the EW-7438RPn web management interface to trusted administrative VLANs only
- Change default and weak administrative credentials, since exploitation requires low-privilege authentication
- Disable remote (WAN-side) management on affected devices
- Inventory deployed Edimax EW-7438RPn units running firmware 1.31 and prioritize replacement planning
Patch Information
No vendor patch is available. According to the CVE record, Edimax was contacted before public disclosure but did not respond. The EW-7438RPn is an end-of-life consumer range extender, and replacement with a currently supported device is the most reliable remediation. Track the VulDB advisory for CVE-2026-9426 for any future vendor updates.
Workarounds
- Place affected devices behind a network segment that blocks inbound HTTP/HTTPS to the management interface from user networks
- Use firewall ACLs to restrict source IPs permitted to reach /goform/formHwSet
- Decommission EW-7438RPn devices in environments where exposure cannot be controlled, and replace with a supported model
# Example firewall rule restricting management access to a trusted admin host
iptables -A FORWARD -p tcp -d <EW-7438RPn-IP> --dport 80 -s <admin-host-IP> -j ACCEPT
iptables -A FORWARD -p tcp -d <EW-7438RPn-IP> --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
