CVE-2026-3044: Tenda AC8 Firmware Buffer Overflow Flaw

CVE-2026-3044 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda AC8 router firmware version 16.03.34.06. This vulnerability affects the webCgiGetUploadFile function within the /cgi-bin/UploadCfg file of the Httpd Service component. An attacker can exploit this flaw by manipulating the boundary argument, potentially leading to remote code execution on the affected device.

Critical Impact

This vulnerability allows remote attackers to trigger a stack-based buffer overflow by sending specially crafted requests to the Httpd Service, potentially enabling complete device compromise and network infiltration.

Affected Products

• Tenda AC8 Firmware version 16.03.34.06
• Tenda AC8 Router Hardware

Discovery Timeline

• 2026-02-24 - CVE-2026-3044 published to NVD
• 2026-02-24 - Last updated in NVD database

Technical Details for CVE-2026-3044

Vulnerability Analysis

This vulnerability exists within the Httpd Service of the Tenda AC8 router, specifically in the webCgiGetUploadFile function responsible for handling configuration file uploads. The function fails to properly validate the length of the boundary parameter in multipart form data requests before copying it to a fixed-size stack buffer.

When a malicious request is sent with an excessively long boundary value, the function writes beyond the allocated stack buffer boundaries, corrupting adjacent stack memory. This memory corruption can overwrite critical stack elements including saved return addresses and function pointers, enabling attackers to redirect program execution flow.

The vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), which encompasses buffer overflow conditions where input data exceeds allocated memory boundaries.

Root Cause

The root cause of this vulnerability is insufficient input validation in the webCgiGetUploadFile function. The function processes the boundary argument from HTTP multipart requests without verifying that its length does not exceed the size of the destination stack buffer. This lack of bounds checking allows attackers to supply an oversized boundary value that overwrites adjacent memory on the stack.

The Httpd Service component runs with elevated privileges on the router, meaning successful exploitation could grant attackers administrative control over the device and its network functions.

Attack Vector

The attack can be initiated remotely over the network by sending malicious HTTP requests to the router's /cgi-bin/UploadCfg endpoint. An attacker with low-level authentication to the router's web interface can craft a multipart form request with a manipulated boundary parameter designed to overflow the stack buffer.

The exploitation mechanism involves:

1. Establishing a connection to the target router's Httpd Service
2. Sending a specially crafted HTTP POST request to /cgi-bin/UploadCfg
3. Including a malformed multipart boundary value exceeding expected buffer size
4. Overwriting the stack return address to redirect execution to attacker-controlled code

The exploit for this vulnerability has been disclosed publicly. For technical details on the vulnerability mechanism, refer to the GitHub Issue for CVE-43 and the VulDB entry.

Detection Methods for CVE-2026-3044

Indicators of Compromise

• Unusual HTTP POST requests to /cgi-bin/UploadCfg with abnormally large Content-Type boundary values
• Unexpected router reboots or service crashes in the Httpd Service
• Unauthorized configuration changes or firmware modifications on Tenda AC8 devices
• Network traffic anomalies originating from the router to unknown external destinations

Detection Strategies

• Implement network intrusion detection rules to monitor for oversized boundary parameters in HTTP multipart requests targeting Tenda devices
• Deploy web application firewall rules to inspect and limit the size of HTTP header fields and multipart boundaries
• Configure logging on network perimeter devices to capture requests to vulnerable CGI endpoints
• Utilize endpoint detection and response (EDR) solutions capable of monitoring embedded device behavior

Monitoring Recommendations

• Monitor network logs for repeated requests to /cgi-bin/UploadCfg endpoints on Tenda devices
• Establish baseline behavior for router management interfaces and alert on deviations
• Review DHCP and ARP tables for unexpected changes that could indicate router compromise
• Implement network segmentation to isolate IoT and router management interfaces from general network traffic

How to Mitigate CVE-2026-3044

Immediate Actions Required

• Restrict network access to the router's web management interface to trusted administrative networks only
• Disable remote management features if not required for operations
• Implement strong firewall rules to block external access to router administration ports
• Monitor for firmware updates from Tenda and apply patches as soon as available

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Administrators should monitor the Tenda Official Website for security updates and firmware releases addressing CVE-2026-3044. Additional vulnerability tracking information is available through VulDB CTI ID #347400.

Workarounds

• Configure access control lists (ACLs) to limit management interface access to specific trusted IP addresses
• Place the router management interface behind a VPN to prevent direct internet exposure
• Consider replacing affected devices with alternative router models if a patch is not released in a timely manner
• Implement network segmentation to minimize blast radius in case of successful exploitation

# Example: Restrict web management access on upstream firewall
# Block external access to router management ports
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP

# Allow only trusted admin subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT