CVE-2026-2911: Tenda FH451 Buffer Overflow Vulnerability

CVE-2026-2911 Overview

A buffer overflow vulnerability has been identified in Tenda FH451 wireless router firmware up to version 1.0.0.9. This issue affects the processing of requests to the /goform/GstDhcpSetSer endpoint, where improper handling of user-supplied input leads to a buffer overflow condition. The vulnerability can be exploited remotely by an authenticated attacker to potentially execute arbitrary code or cause a denial of service on the affected device.

Critical Impact

Remote attackers with low-level privileges can exploit this buffer overflow to compromise Tenda FH451 routers, potentially gaining full control of the device or disrupting network services.

Affected Products

• Tenda FH451 Firmware version 1.0.0.9 and earlier
• Tenda FH451 Hardware

Discovery Timeline

• 2026-02-22 - CVE-2026-2911 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2026-2911

Vulnerability Analysis

This vulnerability exists in the Tenda FH451 router's web management interface, specifically within the /goform/GstDhcpSetSer endpoint which handles DHCP server configuration requests. The firmware fails to properly validate the length of user-supplied input before copying it into fixed-size memory buffers, resulting in a classic buffer overflow condition (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer).

When an authenticated attacker sends specially crafted HTTP requests to the vulnerable endpoint with oversized parameters, the excess data overflows the allocated buffer boundaries. This memory corruption can overwrite adjacent memory structures, potentially including function pointers or return addresses, enabling arbitrary code execution with the privileges of the web server process running on the router.

The vulnerability is accessible over the network, requiring only low-level authentication to exploit. This makes it particularly dangerous in environments where the router's administrative interface is exposed to untrusted networks or where default credentials have not been changed.

Root Cause

The root cause of this vulnerability is insufficient input validation and bounds checking in the /goform/GstDhcpSetSer handler function. The firmware does not properly verify that user-supplied data fits within the allocated buffer size before performing memory copy operations. This programming error is characteristic of unsafe memory handling practices common in embedded device firmware written in C/C++.

Attack Vector

The attack is network-based, allowing remote exploitation without physical access to the device. An attacker must have low-level authentication to the router's web interface. The attack flow involves:

1. Authenticating to the Tenda FH451 web management interface (potentially using default credentials)
2. Sending a malicious HTTP POST request to /goform/GstDhcpSetSer with oversized input parameters
3. The buffer overflow occurs during request processing, corrupting adjacent memory
4. Depending on the memory layout, this can lead to code execution or device crash

The exploit has been publicly disclosed according to vulnerability reports, increasing the risk of active exploitation in the wild. For technical details on the vulnerability mechanism, refer to Ricky's Vulnerability Report on Tenda FH451.

Detection Methods for CVE-2026-2911

Indicators of Compromise

• Unexpected reboots or instability of Tenda FH451 routers
• Unusual HTTP POST requests to /goform/GstDhcpSetSer with abnormally large parameter values
• Evidence of unauthorized configuration changes to DHCP settings
• Suspicious outbound network connections originating from the router

Detection Strategies

• Monitor web server logs on Tenda FH451 devices for POST requests to /goform/GstDhcpSetSer with unusually large payloads
• Deploy network intrusion detection rules to identify HTTP requests targeting vulnerable Tenda firmware endpoints
• Implement network segmentation to isolate router management interfaces from untrusted networks
• Use SentinelOne Singularity™ to monitor for anomalous behavior on network segments containing affected devices

Monitoring Recommendations

• Enable logging on the router's administrative interface and forward logs to a centralized SIEM
• Configure alerts for repeated authentication attempts or unusual administrative access patterns
• Regularly audit DHCP configuration settings for unauthorized modifications
• Monitor network traffic patterns for indicators of router compromise or command-and-control communications

How to Mitigate CVE-2026-2911

Immediate Actions Required

• Restrict access to the Tenda FH451 administrative interface to trusted management networks only
• Change default administrative credentials to strong, unique passwords
• Disable remote management access if not required for operations
• Consider replacing end-of-life devices if no firmware update is available from the vendor
• Implement network segmentation to limit the blast radius of potential compromise

Patch Information

At the time of publication, no official patch information is available from Tenda. Users should monitor the Tenda Official Website for firmware updates addressing this vulnerability. Given the public disclosure of exploit details, applying any available security updates should be considered a high priority.

For additional technical details, refer to the VulDB CTI Report #347220.

Workarounds

• Implement access control lists (ACLs) to restrict administrative interface access to specific trusted IP addresses
• Place the router's management interface on a dedicated VLAN isolated from user traffic
• Deploy a web application firewall (WAF) or reverse proxy to filter malicious requests targeting the vulnerable endpoint
• If the device cannot be patched or replaced, consider deploying network-level IPS rules to block exploit attempts

# Example: iptables rules to restrict management access (apply on upstream firewall)
# Only allow management access from trusted admin subnet
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -s <trusted_admin_subnet> -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -s <trusted_admin_subnet> -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP