CVE-2026-5021: Tenda F453 Buffer Overflow Vulnerability

CVE-2026-5021 Overview

A stack-based buffer overflow vulnerability has been discovered in Tenda F453 firmware version 1.0.0.3. The flaw exists in the fromPPTPUserSetting function within the /goform/PPTPUserSetting endpoint of the httpd component. An authenticated remote attacker can manipulate the delno argument to trigger a stack-based buffer overflow, potentially leading to arbitrary code execution or denial of service on the affected device.

Critical Impact
This vulnerability allows remote authenticated attackers to exploit a stack-based buffer overflow in the Tenda F453 router's web management interface, potentially enabling complete device compromise through arbitrary code execution.

Affected Products

Tenda F453 Firmware version 1.0.0.3
Tenda F453 Hardware

Discovery Timeline

2026-03-29 - CVE-2026-5021 published to NVD
2026-03-30 - Last updated in NVD database

Technical Details for CVE-2026-5021

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-787: Out-of-bounds Write) with an underlying memory corruption issue (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The vulnerable function fromPPTPUserSetting fails to properly validate the length of user-supplied input passed through the delno parameter before copying it to a fixed-size stack buffer.

When processing HTTP requests to /goform/PPTPUserSetting, the httpd service does not implement adequate bounds checking on the delno argument. This allows an attacker to supply an oversized input that exceeds the allocated buffer space on the stack, overwriting adjacent memory including the return address and other critical control data.

The exploit has been publicly disclosed and documented, making this a higher-risk vulnerability for organizations using affected Tenda F453 devices. The network-accessible nature of the httpd service means that any authenticated user with access to the web management interface can potentially exploit this flaw.

Root Cause

The root cause of this vulnerability lies in the fromPPTPUserSetting function's handling of the delno parameter within the PPTP user settings functionality. The function uses unsafe string handling operations that do not validate input length against the destination buffer size. This is a common vulnerability pattern in embedded device firmware where memory-safe programming practices are not consistently applied.

The lack of proper input validation in the httpd web server allows user-controlled data to directly overflow the stack buffer, corrupting the stack frame and enabling control flow hijacking.

Attack Vector

The attack is conducted over the network through HTTP requests to the router's web management interface. An attacker who has obtained valid credentials (or exploiting another authentication bypass) can send a malicious HTTP request to /goform/PPTPUserSetting with a specially crafted delno parameter containing an oversized payload.

The attack flow involves:

The attacker identifies a vulnerable Tenda F453 device running firmware version 1.0.0.3
The attacker authenticates to the web management interface
A crafted HTTP request is sent to /goform/PPTPUserSetting with an excessively long delno value
The overflow corrupts the stack, potentially overwriting the return address
Upon function return, execution flow can be redirected to attacker-controlled code

Technical details regarding the vulnerability are documented in the GitHub Vulnerability Database and the VulDB entry #353906.

Detection Methods for CVE-2026-5021

Indicators of Compromise

Unusual HTTP POST requests to /goform/PPTPUserSetting with abnormally large delno parameter values
Router crashes, unexpected reboots, or httpd service failures
Evidence of unauthorized configuration changes to PPTP user settings
Anomalous network traffic originating from the router indicating potential compromise

Detection Strategies

Monitor HTTP traffic to router management interfaces for requests containing oversized parameters in PPTP-related endpoints
Implement web application firewall rules to detect and block requests with excessively long delno values to /goform/PPTPUserSetting
Configure network intrusion detection systems to alert on buffer overflow attack patterns targeting embedded device web interfaces
Review router access logs for authentication attempts followed by requests to vulnerable endpoints

Monitoring Recommendations

Enable comprehensive logging on network segments containing Tenda F453 devices
Implement network segmentation to isolate router management interfaces from untrusted networks
Deploy anomaly detection for embedded device behavior including unexpected service restarts
Monitor for firmware modification or unauthorized access patterns on IoT network segments

How to Mitigate CVE-2026-5021

Immediate Actions Required

Restrict access to the Tenda F453 web management interface to trusted administrative networks only
Implement strong authentication credentials and change default passwords immediately
Consider placing the router management interface behind a VPN or firewall with strict access controls
Monitor the Tenda Official Website for firmware updates addressing this vulnerability

Patch Information

As of the last update on 2026-03-30, no vendor patch has been officially announced for this vulnerability. Organizations should monitor Tenda's official security channels and support resources for firmware updates. The vulnerability details have been submitted through VulDB Submission #778415, which may prompt vendor response.

Until an official patch is available, organizations should implement the recommended workarounds and consider the risk of continued operation of affected devices.

Workarounds

Disable remote management access to the router's web interface if not required for operations
Implement network-level access controls restricting management interface access to specific trusted IP addresses
Deploy a web application firewall in front of the management interface to filter malicious requests
Consider replacing vulnerable devices with alternative hardware if a patch is not forthcoming

bash

# Configuration example - Restrict management access via firewall
# Block external access to router management port (typically 80/443)
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP