CVE-2026-3729: Tenda F453 Buffer Overflow Vulnerability

CVE-2026-3729 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda F453 routers running firmware version 1.0.0.3. The vulnerability exists in the fromPptpUserAdd function within the /goform/PPTPDClient endpoint, which handles PPTP (Point-to-Point Tunneling Protocol) client configuration. Attackers can exploit this flaw by sending specially crafted values to the username or opttype parameters, triggering a buffer overflow condition that can lead to remote code execution or denial of service.

Critical Impact

Remote attackers with low-privilege access can exploit this vulnerability over the network to potentially execute arbitrary code or crash the affected device, compromising network security.

Affected Products

• Tenda F453 Firmware version 1.0.0.3
• Tenda F453 Hardware Device

Discovery Timeline

• 2026-03-08 - CVE-2026-3729 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3729

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The fromPptpUserAdd function in the Tenda F453 firmware fails to properly validate the length of user-supplied input before copying it to a fixed-size stack buffer. When processing PPTP client configuration requests through the /goform/PPTPDClient endpoint, the function accepts the username and opttype parameters without adequate bounds checking.

The network-accessible nature of this vulnerability combined with low attack complexity makes it particularly dangerous for organizations using affected devices. An attacker with minimal authentication can craft malicious HTTP requests containing oversized parameter values to overflow the stack buffer, potentially overwriting return addresses and gaining control of program execution flow.

Root Cause

The root cause lies in insufficient input validation within the fromPptpUserAdd function. The firmware developers did not implement proper length checks on the username and opttype parameters before copying them to stack-allocated buffers. This oversight allows attacker-controlled data to exceed the allocated buffer size, corrupting adjacent memory on the stack.

Attack Vector

The attack is executed remotely over the network by sending specially crafted HTTP POST requests to the /goform/PPTPDClient endpoint. The attacker must have low-privilege access to the device's web interface. By manipulating the username or opttype parameters with excessively long strings, the attacker can trigger the buffer overflow condition.

The vulnerability mechanism involves HTTP parameter injection through the PPTP client configuration form. When the fromPptpUserAdd function processes the malicious input, it copies the oversized data to a fixed-size stack buffer using an unsafe memory copy operation. This overwrites adjacent stack memory, including saved return addresses, potentially allowing arbitrary code execution. Technical details and proof-of-concept information can be found in the GitHub Vulnerability Database Entry.

Detection Methods for CVE-2026-3729

Indicators of Compromise

• Unusual HTTP POST requests to /goform/PPTPDClient containing abnormally long username or opttype parameter values
• Device crashes or unexpected reboots following web interface access
• Modified PPTP client configurations that were not authorized by administrators
• Network traffic anomalies indicating outbound connections from the router to unknown external hosts

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with oversized parameters targeting Tenda device endpoints
• Monitor web server logs on the device for requests to /goform/PPTPDClient with parameter lengths exceeding normal thresholds
• Deploy network segmentation to isolate management interfaces and detect unauthorized access attempts
• Use behavioral analysis to identify abnormal router behavior indicative of exploitation

Monitoring Recommendations

• Enable logging on all network devices and aggregate logs to a central SIEM for analysis
• Configure alerts for repeated access attempts to router administration interfaces from untrusted networks
• Regularly audit device configurations for unauthorized changes to PPTP client settings
• Monitor for firmware integrity violations or unexpected changes to system files

How to Mitigate CVE-2026-3729

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote administration if not explicitly required for operations
• Implement network segmentation to isolate the router from untrusted network segments
• Monitor device logs for any suspicious activity targeting the PPTP configuration endpoints

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Organizations should monitor the Tenda Official Website for firmware updates addressing CVE-2026-3729. Additional technical information is available through VulDB #349707.

Workarounds

• Disable the PPTP client functionality if not required for business operations
• Implement firewall rules to block external access to the /goform/PPTPDClient endpoint
• Deploy a web application firewall (WAF) in front of the device to filter malicious requests
• Consider replacing the vulnerable device with alternative hardware until a patch is available

# Example: Restrict web interface access via iptables on upstream firewall
# Block external access to the Tenda device management interface
iptables -A FORWARD -d <TENDA_DEVICE_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <TENDA_DEVICE_IP> -p tcp --dport 443 -j DROP

# Allow access only from trusted management subnet
iptables -I FORWARD -s <TRUSTED_MGMT_SUBNET> -d <TENDA_DEVICE_IP> -p tcp --dport 80 -j ACCEPT