CVE-2026-6198: Critical Buffer Overflow Vulnerability in Tenda F456 Router NAT Configuration

Overview

Security researchers have identified a critical vulnerability in Tenda F456 wireless routers that poses significant risks to network infrastructure security. CVE-2026-6198 represents a stack-based buffer overflow vulnerability with a CVSS score of 8.8 (HIGH), affecting the NAT static setting functionality of these widely-deployed consumer and small business networking devices.

The vulnerability exists within the fromNatStaticSetting function, which processes user input for Network Address Translation (NAT) port forwarding configurations. When malicious data is supplied to the page parameter via the /goform/NatStaticSetting endpoint, the function fails to properly validate input length, leading to stack memory corruption. This flaw enables remote attackers to potentially achieve arbitrary code execution on affected devices without authentication.

What makes this vulnerability particularly concerning is its remote attack vector and the fact that exploitation details have been publicly disclosed, significantly lowering the barrier for threat actors to weaponize this flaw against vulnerable installations.

Technical Details

The vulnerability stems from insufficient input validation in the router's web administration interface. The fromNatStaticSetting function, responsible for processing NAT port forwarding rules, uses a fixed-size stack buffer to store incoming data from the page parameter.

When processing HTTP POST requests to /goform/NatStaticSetting, the function copies user-controlled data directly into this stack buffer without performing adequate bounds checking. By supplying a payload exceeding the buffer's allocated size, an attacker can overwrite adjacent stack memory, including return addresses and saved frame pointers.

The overflow occurs in the following sequence:

• User submits malformed data via the web interface NAT configuration page
• The page parameter contains payload exceeding expected length
• Function copies data using unsafe string operations
• Stack corruption occurs, overwriting critical memory regions
• Attacker gains control of program execution flow

This vulnerability is particularly exploitable because the affected function runs with elevated privileges within the router's firmware, potentially granting attackers complete control over the device's operation.

Attack Vector and Exploitation

Exploitation of CVE-2026-6198 can be achieved through multiple attack vectors, with the most common being direct web interface manipulation. Attackers can craft malicious HTTP requests targeting the vulnerable endpoint from either local network positions or, in cases where remote administration is enabled, from external networks.

The attack typically follows this methodology:

1. Reconnaissance: Attacker identifies vulnerable Tenda F456 devices through network scanning or service enumeration
2. Payload Development: Crafting buffer overflow exploit containing shellcode designed for the router's MIPS architecture
3. Delivery: Sending malicious HTTP POST request to /goform/NatStaticSetting with oversized page parameter
4. Execution: Successful overflow redirects execution to attacker-controlled shellcode

The public disclosure of exploitation techniques significantly amplifies the threat landscape, as attackers can leverage existing proof-of-concept code to target vulnerable installations. Additionally, the vulnerability can be integrated into automated attack frameworks targeting IoT devices, potentially leading to large-scale compromise campaigns.

Affected Systems

The vulnerability specifically impacts Tenda F456 wireless routers running firmware version 1.0.0.5. However, security researchers recommend treating all Tenda F456 models as potentially vulnerable until official confirmation from the manufacturer.

Organizations and individuals using these devices in the following configurations face elevated risk:

• Routers with remote administration enabled
• Devices deployed in DMZ configurations
• Systems with default or weak administrative credentials
• Networks where the router's web interface is accessible from untrusted segments

The cross-platform nature of this vulnerability means that exploitation techniques can be adapted across different deployment scenarios, making comprehensive inventory and assessment crucial for affected organizations.

Detection and Indicators of Compromise

Organizations should implement monitoring for several key indicators that may suggest active exploitation attempts or successful compromise:

Network-Level Indicators:

• Unusual HTTP POST requests to /goform/NatStaticSetting with abnormally large payloads
• Unexpected outbound connections from router IP addresses
• DNS queries for suspicious domains originating from networking equipment

Device-Level Indicators:

• Unexpected reboots or stability issues with Tenda F456 devices
• Unauthorized changes to NAT configuration settings
• New port forwarding rules created without administrative action
• Unusual CPU or memory utilization patterns

Security teams should configure network monitoring tools to detect buffer overflow attack signatures and implement logging for all administrative actions on networking equipment.

Remediation

Immediate remediation steps should include:

Short-term Mitigations:

• Disable remote administration capabilities on affected devices
• Restrict web interface access to trusted management networks only
• Implement network segmentation isolating vulnerable devices
• Monitor device logs for suspicious activity

Long-term Solutions:

• Contact Tenda support for firmware updates addressing CVE-2026-6198
• Consider replacing affected devices with alternative solutions if patches are unavailable
• Implement network access control limiting device management interfaces
• Deploy intrusion detection systems monitoring IoT device communications

Organizations should prioritize firmware updates once available, as this vulnerability's high severity and public exploitation details create significant ongoing risk.

CypherByte Assessment

CypherByte's security research team considers CVE-2026-6198 a critical priority for immediate attention. The combination of remote exploitability, high impact potential, and public disclosure creates an elevated threat landscape requiring urgent response.

Our analysis indicates this vulnerability represents broader systemic issues in IoT device security, particularly inadequate input validation in web-based management interfaces. The stack-based buffer overflow pattern observed here is consistent with poor secure coding practices prevalent across consumer networking equipment.

We strongly recommend treating this as a zero-day equivalent threat given the public availability of exploitation techniques. Organizations should assume active scanning and exploitation attempts are already underway and implement defensive measures accordingly.

CypherByte will continue monitoring this vulnerability for emerging exploitation patterns and will update our threat intelligence platforms with relevant indicators as they become available.