CVE-2026-4008 Overview
CVE-2026-4008 is a stack-based buffer overflow in the Tenda W3 router firmware version 1.0.0.3(2204). The flaw resides in the /goform/wifiSSIDset endpoint, where the POST parameter handler fails to validate the index and GO arguments before copying them into a fixed-size stack buffer. An authenticated remote attacker can send a crafted HTTP request to corrupt the stack, crash the device, or potentially execute arbitrary code in the context of the web management service. A public exploit has been disclosed, increasing the likelihood of opportunistic attacks against exposed devices.
Critical Impact
Remote attackers with low-privilege access can trigger memory corruption in the router's web service, leading to denial of service or arbitrary code execution on the device.
Affected Products
- Tenda W3 router (hardware)
- Tenda W3 Firmware version 1.0.0.3(2204)
- Deployments exposing the web management interface (/goform/wifiSSIDset) to untrusted networks
Discovery Timeline
- 2026-03-12 - CVE-2026-4008 published to NVD
- 2026-04-02 - Last updated in NVD database
Technical Details for CVE-2026-4008
Vulnerability Analysis
The vulnerability is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer) and [CWE-787] (Out-of-bounds Write). The flaw exists in the request handler bound to /goform/wifiSSIDset, a CGI-style endpoint that processes Wi-Fi SSID configuration updates submitted via HTTP POST.
When the handler parses the index and GO parameters from the POST body, it copies the attacker-controlled values into a fixed-length stack buffer without enforcing length checks. Supplying values that exceed the buffer size overwrites adjacent stack frames, including the saved return address. On MIPS-based Tenda devices, this commonly enables control of the program counter through ROP-style gadget chains in the device's BusyBox or libc image.
The attack is launched over the network against the device's HTTP administrative interface. The CVSS vector indicates low attacker complexity and a requirement for low-level privileges, consistent with an authenticated session on the router's web UI. Successful exploitation impacts confidentiality, integrity, and availability of the device.
Root Cause
The root cause is missing bounds validation on the index and GO POST parameters before they are passed to an unsafe string copy operation (such as strcpy or sprintf) writing into a stack-allocated buffer in the wifiSSIDset form handler.
Attack Vector
An attacker on the same network as the router, or with access to an exposed management interface, sends a POST request to /goform/wifiSSIDset containing an oversized index or GO parameter. The crafted payload overflows the stack buffer and corrupts saved registers. No user interaction is required beyond authentication to the web UI.
The vulnerability mechanism is documented in the public proof-of-concept repositories published on GitHub. See the GitHub PoC Repository - Buffer Overflow and GitHub PoC Repository - Index Overflow for technical reproduction details.
Detection Methods for CVE-2026-4008
Indicators of Compromise
- Unexpected reboots or crashes of the Tenda W3 router, particularly correlated with HTTP requests to /goform/wifiSSIDset.
- HTTP POST requests to /goform/wifiSSIDset containing abnormally long index or GO parameter values.
- Unauthorized changes to Wi-Fi SSID configuration or administrative credentials.
- Outbound connections from the router to unfamiliar hosts following web UI activity.
Detection Strategies
- Inspect web server and reverse-proxy logs for POST requests to /goform/wifiSSIDset with parameter lengths exceeding expected SSID configuration bounds (typically 32 bytes for SSID values).
- Deploy network IDS/IPS signatures that flag oversized form fields targeting Tenda CGI endpoints.
- Monitor for repeated authentication attempts to the router admin interface followed by configuration POST traffic.
Monitoring Recommendations
- Capture full HTTP request bodies for traffic destined for router management interfaces and retain them for forensic analysis.
- Alert on router availability gaps and correlate with administrative HTTP traffic in the preceding minutes.
- Track firmware version inventory for SOHO devices and flag any Tenda W3 units running 1.0.0.3(2204).
How to Mitigate CVE-2026-4008
Immediate Actions Required
- Restrict access to the Tenda W3 web management interface to trusted management VLANs only; never expose it to the WAN.
- Change default administrative credentials and enforce strong, unique passwords on the router admin account.
- Audit existing devices for the affected firmware version 1.0.0.3(2204) and prioritize remediation for internet-exposed units.
Patch Information
At the time of publication, no official vendor patch is referenced in the available advisories. Check the Tenda Official Website for firmware updates addressing CVE-2026-4008. Additional vulnerability tracking is available at VulDB #350531.
Workarounds
- Disable remote management on the WAN interface and block inbound TCP traffic to the router's HTTP/HTTPS admin ports.
- Place the router behind a firewall that filters unauthorized POST requests to /goform/wifiSSIDset.
- Segment the router management network from user and IoT networks to limit lateral access to the admin interface.
- Consider replacing end-of-support Tenda W3 hardware with currently supported router models if no firmware fix becomes available.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
