CVE-2026-6196: Tenda F456 Buffer Overflow Vulnerability

CVE-2026-6196 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda F456 router firmware version 1.0.0.5. The vulnerability exists in the fromexeCommand function located in the /goform/exeCommand endpoint. By manipulating the cmdinput argument, an attacker can trigger a stack-based buffer overflow condition. This vulnerability is remotely exploitable and a public exploit is available, making affected devices high-priority targets for immediate remediation.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code, compromise device integrity, and gain unauthorized control over affected Tenda F456 routers.

Affected Products

• Tenda F456 Firmware Version 1.0.0.5

Discovery Timeline

• April 13, 2026 - CVE-2026-6196 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6196

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the fromexeCommand function which handles requests to the /goform/exeCommand endpoint on the router's web management interface. When processing the cmdinput parameter, the function fails to properly validate the length of user-supplied input before copying it to a fixed-size stack buffer.

The network-accessible nature of this vulnerability means that any attacker who can reach the router's web management interface can attempt exploitation without requiring physical access to the device. The attack requires low privileges, suggesting that basic authentication to the web interface may be sufficient to reach the vulnerable endpoint.

Root Cause

The root cause of this vulnerability is improper bounds checking in the fromexeCommand function. When the cmdinput argument is processed, the function copies user-controlled data into a stack-allocated buffer without verifying that the input length does not exceed the buffer's capacity. This classic programming error allows attackers to write beyond the intended memory boundaries, potentially overwriting the function's return address or other critical stack data.

Attack Vector

The attack is conducted remotely over the network by sending a specially crafted HTTP request to the /goform/exeCommand endpoint. The attacker manipulates the cmdinput parameter with an oversized payload designed to overflow the stack buffer. By carefully constructing the overflow payload, an attacker can overwrite the saved return address on the stack, potentially redirecting program execution to attacker-controlled code.

The vulnerability mechanism involves sending malicious input to the router's web management interface. When the fromexeCommand function processes an excessively long cmdinput value, the stack buffer is overwritten, leading to potential code execution or denial of service. For detailed technical analysis, see the GitHub Vulnerability Report and VulDB entry #357118.

Detection Methods for CVE-2026-6196

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/exeCommand containing abnormally long cmdinput parameter values
• Router crashes, reboots, or unresponsive behavior following web interface access attempts
• Unusual outbound network connections from the router to unknown external IP addresses
• Modified router configuration settings or unauthorized administrative accounts

Detection Strategies

• Deploy network intrusion detection rules to monitor for HTTP requests to /goform/exeCommand with oversized payloads
• Implement web application firewall rules to block requests containing excessively long parameter values to the router management interface
• Monitor router logs for repeated failed or suspicious requests to the command execution endpoint
• Use SentinelOne Singularity to detect anomalous network traffic patterns associated with buffer overflow exploitation attempts

Monitoring Recommendations

• Enable comprehensive logging on network perimeter devices to capture all traffic destined for router management interfaces
• Establish baseline network behavior for Tenda F456 devices and alert on deviations
• Periodically audit router configurations for unauthorized changes that may indicate compromise
• Implement network segmentation to restrict access to router management interfaces from untrusted network segments

How to Mitigate CVE-2026-6196

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses or management VLANs only
• Disable remote management features if not required for operational purposes
• Place affected Tenda F456 routers behind a firewall that blocks external access to the management interface
• Monitor for firmware updates from Tenda and apply patches immediately when available

Patch Information

At the time of publication, no official patch has been confirmed from Tenda. Administrators should monitor the Tenda Official Website for security advisories and firmware updates. Additional technical details and exploit information are available through the VulDB Submission #797467 and VulDB CTI entry.

Workarounds

• Implement access control lists (ACLs) to restrict management interface access to specific trusted hosts
• Deploy network-level protections such as firewalls or VPNs to limit exposure of the vulnerable endpoint
• Consider replacing affected devices with models from vendors with faster security response capabilities if patches are not forthcoming
• Use intrusion prevention systems configured to block known buffer overflow attack patterns

# Example firewall rule to restrict access to router management interface
# Block external access to the vulnerable endpoint on port 80/443
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