CVE-2026-4567: Tenda A15 Buffer Overflow Vulnerability

CVE-2026-4567 Overview

CVE-2026-4567 is a stack-based buffer overflow vulnerability in the Tenda A15 router running firmware version 15.13.07.13. The flaw resides in the UploadCfg function within /cgi-bin/UploadCfg, where manipulation of the File argument corrupts the call stack. An unauthenticated remote attacker can trigger the condition over the network without user interaction. Public exploit details have been disclosed, increasing the risk of opportunistic exploitation against exposed devices. The vulnerability is tracked under [CWE-119] for improper restriction of operations within memory buffer bounds.

Critical Impact
Unauthenticated attackers can corrupt stack memory on affected Tenda A15 routers, potentially leading to arbitrary code execution or device crash.

Affected Products

Tenda A15 hardware device
Tenda A15 firmware version 15.13.07.13
Deployments exposing /cgi-bin/UploadCfg to untrusted networks

Discovery Timeline

2026-03-23 - CVE-2026-4567 published to NVD
2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-4567

Vulnerability Analysis

The vulnerability exists in the UploadCfg handler exposed through the /cgi-bin/UploadCfg endpoint on the Tenda A15 router. The handler processes the File parameter without enforcing length boundaries before copying the value into a fixed-size stack buffer. Sending an oversized value overruns adjacent stack memory, including saved return addresses and frame pointers.

Because the endpoint is reachable over the network and requires no authentication, an attacker can deliver the malicious request directly to the device's web management interface. Successful exploitation can hijack control flow, redirect execution to attacker-supplied data, or destabilize the device. Embedded MIPS-class devices like the A15 typically lack robust mitigations such as full ASLR and stack canaries, which simplifies exploit development.

Root Cause

The root cause is missing bounds validation on the File argument inside the UploadCfg function. The code copies attacker-controlled input into a stack-allocated buffer using an unsafe string operation, classifying the defect under [CWE-119]. No length check or output truncation prevents the write from exceeding the destination buffer.

Attack Vector

Exploitation occurs over the network against the router's HTTP management interface. An attacker crafts an HTTP request to /cgi-bin/UploadCfg containing an oversized File parameter and sends it directly to the device. Public technical disclosure is referenced in the GitHub Issue for CVE and the GitHub File Upload Exploit archive. Additional metadata is tracked at VulDB #352404.

No verified code example is available. Refer to the linked advisories for proof-of-concept details.

Detection Methods for CVE-2026-4567

Indicators of Compromise

HTTP POST requests to /cgi-bin/UploadCfg containing abnormally long File parameter values
Unexpected reboots, watchdog resets, or service crashes on Tenda A15 devices following inbound HTTP traffic
Outbound connections from the router to unfamiliar hosts after suspect requests
Configuration changes or new administrative sessions originating from external IP addresses

Detection Strategies

Inspect web application firewall (WAF) and IDS logs for oversized multipart upload fields targeting /cgi-bin/UploadCfg
Deploy network signatures that flag HTTP requests to Tenda CGI endpoints with payload sizes exceeding expected configuration file dimensions
Correlate router crash events with preceding inbound HTTP traffic from public IP ranges

Monitoring Recommendations

Forward router syslog and HTTP access logs to a centralized SIEM for retention and correlation
Alert on any external source attempting to reach the device management interface
Track firmware versions across the fleet to identify devices still running 15.13.07.13

How to Mitigate CVE-2026-4567

Immediate Actions Required

Restrict access to the router web management interface to trusted internal networks only
Disable remote WAN-side administration on all Tenda A15 devices
Place affected devices behind a network segment that blocks unsolicited inbound HTTP traffic
Audit device logs for prior exploitation attempts against /cgi-bin/UploadCfg

Patch Information

At the time of publication, no vendor patch is referenced in the NVD entry. Monitor the Tenda Official Website for firmware updates superseding version 15.13.07.13. Until a fix is released, treat the device as unsupported on untrusted networks.

Workarounds

Block external access to TCP ports hosting the device HTTP management interface at the perimeter firewall
Replace affected hardware with a supported model if patches remain unavailable
Enforce strong network segmentation between consumer-grade routers and sensitive internal assets
Disable Universal Plug and Play (UPnP) and remote management features that may expose the CGI endpoint

bash

# Example perimeter rule blocking external access to router HTTP management
iptables -A INPUT -p tcp --dport 80 -i wan0 -j DROP
iptables -A INPUT -p tcp --dport 443 -i wan0 -j DROP