CVE-2026-5548: Tenda AC10 Buffer Overflow Vulnerability

CVE-2026-5548 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda AC10 routers running firmware version 16.03.10.10_multi_TDE01. The vulnerability exists in the fromSysToolChangePwd function within the /bin/httpd binary. An attacker can exploit this flaw by manipulating the sys.userpass argument, potentially achieving remote code execution on affected devices.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to execute arbitrary code, potentially gaining complete control over the affected Tenda AC10 router without physical access.

Affected Products

• Tenda AC10 Router
• Firmware Version 16.03.10.10_multi_TDE01
• /bin/httpd Web Server Component

Discovery Timeline

• 2026-04-05 - CVE-2026-5548 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-5548

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The fromSysToolChangePwd function in the Tenda AC10's embedded web server fails to properly validate the length of user-supplied input passed through the sys.userpass parameter. When an attacker provides an overly long password value, the function writes beyond the allocated stack buffer boundaries, corrupting adjacent memory regions.

Stack-based buffer overflows in embedded devices like routers are particularly dangerous because these systems often lack modern memory protection mechanisms such as ASLR (Address Space Layout Randomization) or stack canaries. This allows attackers to reliably overwrite return addresses or function pointers to redirect execution flow.

Root Cause

The root cause stems from insufficient input validation in the password change functionality. The fromSysToolChangePwd function uses unsafe string handling operations that do not verify the length of the sys.userpass argument before copying it into a fixed-size stack buffer. This classic buffer overflow pattern allows data to overflow into adjacent stack memory, including saved return addresses.

Attack Vector

The attack can be initiated remotely over the network by sending a specially crafted HTTP request to the router's web management interface. An authenticated attacker with low privileges can target the password change endpoint, supplying a maliciously long sys.userpass value. The attack requires no user interaction and can be executed from any device with network access to the router's management interface.

The exploitation flow involves sending an HTTP POST request to the vulnerable endpoint with an oversized password parameter. When processed by fromSysToolChangePwd, the overflow corrupts stack memory, enabling the attacker to hijack program execution.

Detection Methods for CVE-2026-5548

Indicators of Compromise

• Unusual HTTP POST requests to the router's password change endpoint with abnormally large payload sizes
• Unexpected router reboots or system instability following web interface access
• Unexplained changes to router configuration or firmware
• Network traffic anomalies originating from the router to unknown external destinations

Detection Strategies

• Monitor network traffic for HTTP requests to Tenda AC10 management interfaces containing oversized sys.userpass parameters
• Implement intrusion detection rules to alert on buffer overflow attack patterns targeting embedded device web interfaces
• Deploy network segmentation to isolate IoT and router management interfaces from general network traffic
• Review router access logs for authentication attempts with anomalous parameter lengths

Monitoring Recommendations

• Enable logging on the router management interface and forward logs to a centralized SIEM solution
• Implement network-based anomaly detection to identify exploitation attempts
• Regularly audit devices on the network for vulnerable firmware versions
• Configure alerts for any configuration changes on network infrastructure devices

How to Mitigate CVE-2026-5548

Immediate Actions Required

• Restrict access to the Tenda AC10 web management interface to trusted IP addresses only
• Disable remote management access if not required for operations
• Place the router behind a firewall that filters incoming connections to the management port
• Monitor for firmware updates from Tenda that address this vulnerability

Patch Information

At the time of publication, no official patch has been released by Tenda. Administrators should monitor the Tenda Official Website for security advisories and firmware updates. Additional technical details about this vulnerability are available in the GitHub Vulnerability Findings and VulDB Vulnerability Entry.

Workarounds

• Implement network ACLs to restrict management interface access to specific administrator IP addresses
• Use a VPN to access the router management interface rather than exposing it directly
• Consider replacing affected devices with alternatives that receive regular security updates
• Deploy a web application firewall (WAF) in front of the management interface to filter malicious requests

# Example: Restrict management access using iptables on upstream firewall
iptables -A FORWARD -d <router_management_ip> -p tcp --dport 80 -s <trusted_admin_ip> -j ACCEPT
iptables -A FORWARD -d <router_management_ip> -p tcp --dport 80 -j DROP