CVE-2026-6133: Tenda F451 Buffer Overflow Vulnerability

CVE-2026-6133 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda F451 router firmware version 1.0.0.7_cn_svn7958. This vulnerability affects the fromSafeUrlFilter function within the /goform/SafeUrlFilter endpoint. Malicious manipulation of the page argument enables attackers to trigger a stack-based buffer overflow, potentially leading to remote code execution or denial of service conditions. The exploit has been publicly disclosed and may be actively used in attacks targeting vulnerable Tenda devices.

Critical Impact

Remote attackers with low privileges can exploit this stack-based buffer overflow to compromise Tenda F451 routers, potentially gaining complete control over the device or causing service disruption across network infrastructure.

Affected Products

• Tenda F451 firmware version 1.0.0.7_cn_svn7958

Discovery Timeline

• April 12, 2026 - CVE-2026-6133 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6133

Vulnerability Analysis

This vulnerability represents a classic stack-based buffer overflow (CWE-119) affecting memory boundary operations within embedded router firmware. The fromSafeUrlFilter function processes user-supplied input through the page argument without implementing adequate bounds checking. When an attacker provides oversized or specially crafted input data, the function writes beyond the allocated stack buffer boundaries, corrupting adjacent memory regions.

The network-accessible nature of this vulnerability significantly increases its risk profile. Authentication requirements are low, meaning attackers with minimal access privileges can successfully exploit this flaw. Successful exploitation can result in high impact to confidentiality, integrity, and availability of the affected device.

Root Cause

The root cause stems from improper memory boundary enforcement within the fromSafeUrlFilter function. When processing the page parameter from HTTP requests to /goform/SafeUrlFilter, the function allocates a fixed-size stack buffer but fails to validate that incoming data fits within those boundaries. This classic buffer overflow pattern allows attackers to overwrite return addresses, function pointers, or other critical stack data structures.

Attack Vector

The attack is executed remotely over the network by sending a crafted HTTP request to the /goform/SafeUrlFilter endpoint. An attacker constructs a malicious request containing an oversized or specially formatted page parameter. When the vulnerable fromSafeUrlFilter function processes this input, the overflow condition occurs. Depending on the attacker's payload construction, this can lead to:

• Arbitrary code execution by overwriting the return address
• Denial of service through memory corruption
• Information disclosure if sensitive stack data can be leaked

The vulnerability mechanism involves improper input validation when the fromSafeUrlFilter function handles the page argument. The function copies user-supplied data into a stack-allocated buffer without verifying the input length against buffer capacity. For detailed technical analysis and proof-of-concept information, refer to the GitHub CVE Issue Discussion and VulDB Vulnerability #356997.

Detection Methods for CVE-2026-6133

Indicators of Compromise

• Abnormally large HTTP POST requests targeting /goform/SafeUrlFilter endpoint
• Router crashes or unexpected reboots following web interface access
• Suspicious network traffic patterns to router management interfaces
• Evidence of unauthorized configuration changes or firmware modifications

Detection Strategies

• Monitor HTTP traffic for requests to /goform/SafeUrlFilter with unusually large page parameters
• Implement intrusion detection rules to flag buffer overflow attack patterns against Tenda devices
• Deploy web application firewall rules to inspect and block malformed requests to router endpoints
• Enable comprehensive logging on network segments where Tenda routers are deployed

Monitoring Recommendations

• Configure alerts for repeated or automated requests to Tenda router administration interfaces
• Monitor for signs of router compromise including unexpected DNS changes or traffic redirection
• Implement network segmentation to isolate IoT and router management interfaces from user networks
• Review router access logs regularly for anomalous authentication attempts or administrative actions

How to Mitigate CVE-2026-6133

Immediate Actions Required

• Restrict network access to the router's web management interface to trusted IP addresses only
• Disable remote management features if not required for operations
• Implement network-level access controls to prevent unauthorized access to /goform/SafeUrlFilter
• Consider deploying affected routers behind additional security appliances with deep packet inspection

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Users should monitor the Tenda Official Website for firmware updates addressing CVE-2026-6133. Additional vulnerability details are available through VulDB Submission #792875 and VulDB CTI for #356997.

Workarounds

• Implement strict firewall rules blocking external access to port 80/443 on vulnerable Tenda devices
• Utilize VLAN segmentation to isolate router management interfaces from general network traffic
• Consider replacing affected Tenda F451 devices with alternative hardware until a patch is available
• Deploy network intrusion prevention systems (IPS) with signatures for buffer overflow attacks

# Example iptables rules to restrict access to router management
# Replace 192.168.1.1 with your router's IP and 10.0.0.0/24 with trusted admin network

# Block all external access to router web interface
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP

# Allow only trusted network to access management interface
iptables -I FORWARD -s 10.0.0.0/24 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s 10.0.0.0/24 -d 192.168.1.1 -p tcp --dport 443 -j ACCEPT