CVE-2026-2877: Tenda A18 Buffer Overflow Vulnerability

CVE-2026-2877 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda A18 router firmware version 15.13.07.13. This vulnerability affects the strcpy function within the /goform/WifiExtraSet endpoint of the Httpd Service component. An attacker can exploit this flaw by manipulating the wpapsk_crypto5g argument, leading to memory corruption and potential remote code execution.

Critical Impact

This vulnerability allows remote attackers with low privileges to compromise the confidentiality, integrity, and availability of affected Tenda A18 devices through network-based attacks targeting the web management interface.

Affected Products

• Tenda A18 Firmware version 15.13.07.13
• Tenda A18 Hardware devices running vulnerable firmware

Discovery Timeline

• 2026-02-21 - CVE-2026-2877 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2026-2877

Vulnerability Analysis

This vulnerability stems from improper input validation in the Tenda A18 router's web management interface. The strcpy function, which does not perform bounds checking, is used to copy user-supplied data from the wpapsk_crypto5g parameter into a fixed-size stack buffer. When an attacker provides input exceeding the buffer's allocated size, the excess data overwrites adjacent memory on the stack, including potentially critical control structures such as the return address.

The vulnerability is accessible remotely through the device's Httpd Service, specifically via the /goform/WifiExtraSet endpoint. This endpoint handles WiFi configuration settings and accepts the wpapsk_crypto5g parameter as part of WPA-PSK cryptographic configuration for the 5GHz band. The exploit has been publicly disclosed and may be actively used in attacks.

Root Cause

The root cause is the use of the unsafe strcpy function without proper input length validation. The strcpy function copies data until it encounters a null terminator, with no regard for destination buffer size. This classic programming error allows attackers to overflow the stack buffer by supplying an overly long string value for the wpapsk_crypto5g parameter. Modern secure coding practices mandate the use of bounds-checking alternatives such as strncpy or strlcpy to prevent such vulnerabilities.

Attack Vector

The attack can be initiated remotely over the network by an authenticated attacker with low-privilege access to the device's web interface. The attacker sends a specially crafted HTTP request to the /goform/WifiExtraSet endpoint containing a malicious wpapsk_crypto5g parameter value. The oversized input triggers the buffer overflow, potentially allowing the attacker to:

1. Overwrite the return address to redirect execution flow
2. Inject and execute arbitrary shellcode
3. Cause a denial of service by crashing the Httpd Service
4. Gain complete control over the affected device

The attack does not require user interaction and can be executed in a single HTTP request. The vulnerability affects the device's network-exposed management interface, making internet-exposed devices particularly at risk.

Detection Methods for CVE-2026-2877

Indicators of Compromise

• Unusual HTTP POST requests to /goform/WifiExtraSet containing abnormally long wpapsk_crypto5g parameter values
• Httpd Service crashes or unexpected restarts on Tenda A18 devices
• Suspicious network traffic patterns targeting the device's web management port (typically port 80 or 443)
• Evidence of unauthorized configuration changes or firmware modifications

Detection Strategies

• Deploy network intrusion detection systems (IDS) with rules to detect oversized HTTP parameters targeting Tenda device endpoints
• Monitor HTTP traffic for requests to /goform/WifiExtraSet with payload sizes exceeding normal WiFi configuration parameters
• Implement anomaly detection for repeated crashes or restarts of the Httpd Service on Tenda devices
• Enable verbose logging on network firewalls to capture and analyze traffic to router management interfaces

Monitoring Recommendations

• Regularly review access logs from Tenda A18 devices for unauthorized access attempts
• Configure network monitoring tools to alert on traffic to router management interfaces from untrusted sources
• Implement network segmentation to isolate IoT and network devices from general user traffic
• Deploy endpoint detection and response (EDR) solutions capable of monitoring embedded device behavior

How to Mitigate CVE-2026-2877

Immediate Actions Required

• Disable remote management access to the Tenda A18 web interface from untrusted networks
• Implement network-level access controls to restrict access to the device's management interface
• Place Tenda A18 devices behind a firewall with strict ingress filtering
• Monitor for and apply firmware updates from Tenda when available

Patch Information

At the time of publication, no vendor patch has been officially announced for this vulnerability. Users should monitor the Tenda Official Website for security advisories and firmware updates. Additional technical details are available through the GitHub CVE Issue Discussion and VulDB CTI Incident Report.

Workarounds

• Restrict access to the web management interface to trusted IP addresses only using firewall rules
• Disable the web management interface entirely if not required for device administration
• Use a VPN to access the device management interface rather than exposing it directly to the network
• Consider replacing vulnerable devices with alternative hardware until patches become available

# Example firewall rule to restrict access to Tenda management interface
# Allow only trusted admin IP to access the router web interface
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP

# Block external access to management interface
iptables -A INPUT -p tcp --dport 80 -i eth0 -j DROP