CVE-2026-4567: Tenda A15 Buffer Overflow Vulnerability

CVE-2026-4567 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda A15 router firmware version 15.13.07.13. The vulnerability exists in the UploadCfg function located at /cgi-bin/UploadCfg, where improper handling of the File argument allows attackers to trigger a memory corruption condition. This flaw can be exploited remotely without authentication, potentially leading to arbitrary code execution or denial of service on affected devices.

Critical Impact

Remote attackers can exploit this unauthenticated stack-based buffer overflow to potentially gain control of affected Tenda A15 routers, compromise network security, or render devices inoperable.

Affected Products

• Tenda A15 Router Firmware Version 15.13.07.13

Discovery Timeline

• 2026-03-23 - CVE-2026-4567 published to NVD
• 2026-03-23 - Last updated in NVD database

Technical Details for CVE-2026-4567

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The UploadCfg function in the Tenda A15 router's web management interface fails to properly validate the size of user-supplied input when processing the File argument. When an attacker sends a specially crafted request to the /cgi-bin/UploadCfg endpoint, the oversized input overwrites adjacent memory on the stack, corrupting control flow data such as return addresses or saved frame pointers.

The vulnerability is particularly severe because it does not require authentication, meaning any attacker with network access to the router's management interface can attempt exploitation. The network-based attack vector with low complexity makes this an attractive target for threat actors seeking to compromise home or small office network infrastructure.

Root Cause

The root cause of this vulnerability is insufficient bounds checking in the UploadCfg function when processing the File parameter. The function allocates a fixed-size stack buffer to store incoming data but does not verify that the supplied input length fits within the allocated buffer space before copying the data. This classic buffer overflow pattern allows attackers to write beyond the intended buffer boundaries.

Attack Vector

The attack is conducted remotely over the network by sending a maliciously crafted HTTP request to the /cgi-bin/UploadCfg endpoint on the vulnerable Tenda A15 device. The attacker manipulates the File argument to include payload data that exceeds the expected buffer size. Upon processing this request, the overflow occurs, potentially allowing the attacker to overwrite the function's return address and redirect execution to attacker-controlled code.

The vulnerability can be triggered without any prior authentication to the device, significantly lowering the barrier to exploitation. An attacker simply needs network access to the router's management interface, which may be exposed on the LAN or, in misconfigured deployments, accessible from the internet.

For technical details on the exploitation mechanism, refer to the GitHub Issue Discussion where the vulnerability has been publicly documented.

Detection Methods for CVE-2026-4567

Indicators of Compromise

• Unexpected HTTP POST requests to /cgi-bin/UploadCfg containing abnormally large File parameter values
• Router crashes, reboots, or unresponsive behavior following network requests to the management interface
• Unusual outbound network connections from the router indicating potential compromise
• Modified router configuration or firmware without administrator action

Detection Strategies

• Implement network intrusion detection rules to monitor for oversized HTTP POST requests targeting /cgi-bin/UploadCfg endpoints
• Deploy web application firewalls (WAF) at the network perimeter to inspect and block malformed requests to IoT device management interfaces
• Configure SIEM alerts for repeated connection attempts or error responses from router management services
• Monitor for firmware integrity changes using hash verification against known-good firmware images

Monitoring Recommendations

• Enable logging on network firewalls and review logs for connections to router management ports (typically 80/443)
• Implement network segmentation to isolate IoT devices and limit exposure of management interfaces
• Configure SentinelOne agents on endpoints to detect lateral movement attempts that may follow router compromise
• Regularly audit network device configurations for unauthorized changes

How to Mitigate CVE-2026-4567

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management features if not required for operations
• Place affected Tenda A15 devices behind a firewall that blocks external access to management ports
• Monitor for firmware updates from Tenda and apply patches as soon as they become available
• Consider replacing affected devices with alternatives if no patch is released

Patch Information

At the time of publication, no official patch from Tenda has been confirmed for this vulnerability. Organizations should monitor the Tenda Official Homepage for security advisories and firmware updates addressing this issue. Additional vulnerability tracking information is available at VulDB #352404.

Workarounds

• Implement access control lists (ACLs) on the network to restrict access to the /cgi-bin/UploadCfg endpoint
• Disable the web management interface entirely if alternative management methods are available
• Deploy a reverse proxy with request size limits in front of the management interface
• Segment the network to ensure the router management interface is not accessible from untrusted networks

# Example firewall rule to restrict access to router management interface
# Replace 192.168.1.1 with your router's IP and 192.168.1.100 with trusted admin IP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP