CVE-2026-9380 Overview
CVE-2026-9380 is a buffer overflow vulnerability in the Edimax BR-6675nD router running firmware version 1.12. The flaw resides in the formL2TPSetup function within /goform/formL2TPSetup, part of the device's POST request handler. Attackers can trigger the overflow by manipulating the L2TPUserName argument. The vulnerability is exploitable remotely over the network and a public exploit disclosure is available. The vendor was contacted prior to publication but did not respond, leaving affected devices without an official fix. The issue is tracked under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).
Critical Impact
Remote attackers with low privileges can corrupt memory on the router, potentially achieving arbitrary code execution and full compromise of the device.
Affected Products
- Edimax BR-6675nD firmware version 1.12
- /goform/formL2TPSetup POST request handler component
- formL2TPSetup function processing L2TPUserName parameter
Discovery Timeline
- 2026-05-24 - CVE-2026-9380 published to NVD
- 2026-05-26 - Last updated in NVD database
Technical Details for CVE-2026-9380
Vulnerability Analysis
The vulnerability resides in the formL2TPSetup handler exposed through the router's web management interface at /goform/formL2TPSetup. When the device processes a POST request configuring Layer 2 Tunneling Protocol (L2TP) settings, the L2TPUserName argument is copied into a fixed-size buffer without adequate length validation. Supplying an oversized value overflows the destination buffer and corrupts adjacent memory.
Memory corruption in embedded routers commonly leads to process crashes, denial of service, or hijacked control flow. Because the affected binary typically runs with elevated privileges on the device, successful exploitation can grant attackers control over routing, DNS, and traffic inspection on the local network.
Root Cause
The root cause is missing bounds checking on attacker-controlled input inside formL2TPSetup. The handler accepts the L2TPUserName string from the HTTP POST body and writes it to a stack or static buffer using an unsafe string operation. This pattern, classified as [CWE-119], is widespread in legacy SOHO router firmware where C string handling lacks length-aware wrappers.
Attack Vector
An attacker authenticated with low privileges to the router's administrative interface submits a crafted POST request to /goform/formL2TPSetup. The L2TPUserName field carries a payload longer than the expected buffer size. The malformed request reaches the vulnerable function, which writes past the buffer boundary and corrupts adjacent memory regions. Depending on the binary layout and presence of memory protections, the attacker can crash the service or pivot toward arbitrary code execution on the router.
Further technical details are documented in the Edimax BR-6675nD formL2TPSetup writeup and the VulDB entry #365343.
Detection Methods for CVE-2026-9380
Indicators of Compromise
- POST requests to /goform/formL2TPSetup containing abnormally long L2TPUserName values
- Router reboots, web interface crashes, or httpd process restarts following inbound HTTP traffic
- Unexpected changes to L2TP configuration or new administrative sessions from untrusted source IPs
Detection Strategies
- Inspect HTTP request bodies destined for the router management interface and flag parameter values exceeding documented field lengths
- Alert on repeated POSTs to /goform/formL2TPSetup from a single source, which often signal fuzzing or exploitation attempts
- Correlate router log anomalies with management-plane HTTP traffic to identify exploitation patterns
Monitoring Recommendations
- Forward router syslog data to a centralized logging platform to retain evidence of crashes and configuration changes
- Monitor north-south traffic to router management ports (80/tcp, 443/tcp) for unauthorized access attempts
- Track DNS and routing configuration drift on Edimax devices as a downstream indicator of compromise
How to Mitigate CVE-2026-9380
Immediate Actions Required
- Restrict access to the router's web management interface to trusted internal hosts only and disable WAN-side administration
- Change default and reused administrative credentials to limit who can reach the authenticated POST handler
- Place affected Edimax BR-6675nD devices behind a network segment that blocks untrusted access to management endpoints
Patch Information
No vendor patch is available. Edimax was contacted regarding the disclosure but did not respond. Organizations operating the BR-6675nD 1.12 should plan to replace the device with a supported model or apply compensating network controls until a fix is published. Track updates via the VulDB vulnerability record.
Workarounds
- Disable L2TP configuration features on the device if they are not required for operations
- Use an upstream firewall or access control list to block external requests to /goform/formL2TPSetup
- Segment the router away from sensitive systems and route critical traffic through a supported, patched gateway
# Example: block external access to the router management interface
iptables -A INPUT -p tcp --dport 80 ! -s 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 ! -s 192.168.1.0/24 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
