CVE-2026-3811: Tenda FH1202 Buffer Overflow Vulnerability

CVE-2026-3811 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda FH1202 router firmware version 1.2.0.14(408). This vulnerability affects the fromP2pListFilter function within the /goform/P2pListFilter file. An attacker can exploit this flaw by manipulating the page argument, leading to a stack-based buffer overflow condition that can be triggered remotely. The exploit has been publicly disclosed, increasing the risk of active exploitation.

Critical Impact

This stack-based buffer overflow vulnerability allows remote authenticated attackers to potentially execute arbitrary code or cause denial of service on affected Tenda FH1202 routers, compromising network security and device integrity.

Affected Products

• Tenda FH1202 Firmware version 1.2.0.14(408)
• Tenda FH1202 Hardware

Discovery Timeline

• 2026-03-09 - CVE-2026-3811 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3811

Vulnerability Analysis

This vulnerability exists in the fromP2pListFilter function, which handles P2P (peer-to-peer) list filtering operations on the Tenda FH1202 router. The function fails to properly validate the length of user-supplied input passed through the page parameter before copying it into a fixed-size stack buffer. This improper buffer handling (CWE-119) creates a classic stack-based buffer overflow condition.

When an attacker sends a specially crafted HTTP request to the /goform/P2pListFilter endpoint with an oversized page parameter value, the function writes beyond the allocated stack buffer boundaries. This can corrupt adjacent stack memory, potentially overwriting the return address and allowing an attacker to hijack program execution flow.

Root Cause

The root cause of this vulnerability is insufficient input validation in the fromP2pListFilter function. The function does not implement proper boundary checks on the page argument before performing memory copy operations. Without these checks, the function accepts arbitrarily long input strings that exceed the allocated buffer size on the stack, resulting in a buffer overflow condition.

Attack Vector

The attack can be executed remotely over the network against the router's web management interface. An authenticated attacker with low privileges can send a malicious HTTP POST request to the /goform/P2pListFilter endpoint. By crafting the page parameter with excessive data, the attacker triggers the buffer overflow condition.

The vulnerability exploitation flow involves:

1. Attacker establishes a connection to the router's web interface
2. A crafted HTTP request is sent to /goform/P2pListFilter with an oversized page parameter
3. The fromP2pListFilter function processes the malicious input without proper bounds checking
4. Stack buffer overflow occurs, potentially allowing code execution or causing device crash

Technical details and proof-of-concept information are available in the GitHub PoC Repository.

Detection Methods for CVE-2026-3811

Indicators of Compromise

• Unusual or malformed HTTP POST requests targeting /goform/P2pListFilter endpoint
• Abnormally large page parameter values in web server logs
• Unexpected router crashes or reboots without user intervention
• Anomalous network traffic patterns originating from or directed at the router's management interface

Detection Strategies

• Monitor HTTP traffic to the router's web management interface for requests containing oversized parameters to /goform/P2pListFilter
• Implement intrusion detection rules to flag POST requests with abnormally large page parameter values
• Deploy network monitoring to detect exploitation attempts targeting Tenda router endpoints
• Review web server access logs for patterns consistent with buffer overflow exploitation attempts

Monitoring Recommendations

• Enable comprehensive logging on network firewalls and IDS/IPS systems monitoring traffic to Tenda devices
• Configure alerts for repeated failed authentication attempts or suspicious activity targeting the router management interface
• Implement network segmentation to isolate IoT and networking devices from critical infrastructure
• Conduct regular firmware version audits to identify vulnerable Tenda FH1202 devices in the environment

How to Mitigate CVE-2026-3811

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Implement firewall rules to block external access to the router's administrative ports
• Monitor for firmware updates from Tenda and apply patches immediately when available
• Consider replacing affected devices if vendor patches are not forthcoming
• Disable remote management features if not required for operations

Patch Information

As of the last update on 2026-03-09, no official patch has been released by Tenda for this vulnerability. Users should monitor the Tenda Official Website for security advisories and firmware updates. Additional vulnerability details can be found at VulDB #349777.

Workarounds

• Disable remote administration access to the router's web interface
• Implement network access control lists (ACLs) to limit management interface access to authorized IP addresses only
• Place the router behind a properly configured firewall that filters malicious requests
• Consider using a VPN for remote management instead of exposing the web interface directly
• Segment the network to minimize potential impact if the device is compromised

# Example: Restrict management interface access via iptables (on upstream firewall)
# Block external access to router management port
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 management access only from trusted admin workstation
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT