CVE-2025-11525: Tenda AC7 Buffer Overflow Vulnerability

CVE-2025-11525 Overview

CVE-2025-11525 is a stack-based buffer overflow vulnerability in the Tenda AC7 router running firmware version 15.03.06.44. The flaw resides in an unknown function inside /goform/SetUpnpCfg, where the upnpEn argument is not properly validated before being copied to a fixed-size stack buffer. Attackers can trigger the overflow remotely over the network. The exploit details have been publicly disclosed, increasing the risk of opportunistic attacks against exposed devices. The weakness is tracked under CWE-119, improper restriction of operations within the bounds of a memory buffer.

Critical Impact
Remote attackers with low privileges can corrupt stack memory on the router, enabling code execution or device crashes that disrupt network availability.

Affected Products

Tenda AC7 hardware revision 1.0
Tenda AC7 firmware version 15.03.06.44
Deployments exposing the web management interface (/goform/SetUpnpCfg) to untrusted networks

Discovery Timeline

2025-10-09 - CVE-2025-11525 published to the National Vulnerability Database
2025-10-09 - Last updated in NVD database

Technical Details for CVE-2025-11525

Vulnerability Analysis

The vulnerability exists in the HTTP handler for the /goform/SetUpnpCfg endpoint on the Tenda AC7 router. The handler accepts a user-supplied upnpEn parameter intended to toggle Universal Plug and Play (UPnP) configuration. The parameter value is copied into a fixed-size stack buffer without sufficient length validation, producing a classic stack-based buffer overflow [CWE-119].

Because the overflow occurs on the stack, an attacker controlling the contents of upnpEn can overwrite the saved return address and adjacent local variables. On embedded MIPS-based Tenda devices, this commonly results in arbitrary code execution or a watchdog-triggered reboot. The attack requires network access to the device's web interface and low-privilege authentication.

Root Cause

The root cause is the absence of bounds checking when handling the upnpEn HTTP parameter inside the SetUpnpCfg form handler. The firmware uses unsafe string operations that copy attacker-controlled input directly into a stack buffer of fixed size. This pattern is common in Tenda's httpd binary, where multiple /goform/* endpoints reuse similar unsafe parsing logic.

Attack Vector

An attacker reachable on the same network as the router sends a crafted HTTP POST request to /goform/SetUpnpCfg with an oversized upnpEn value. Authentication is required but only at a low privilege level. Once the malformed request is processed by httpd, the overflow corrupts the saved return address, redirecting execution to attacker-controlled data on the stack.

The public proof-of-concept documentation references the upnpEn field as the overflow trigger. See the GitHub IoT Vulnerability Documentation and VulDB entry #327663 for technical details on the affected endpoint and parameter.

Detection Methods for CVE-2025-11525

Indicators of Compromise

HTTP POST requests to /goform/SetUpnpCfg containing abnormally long upnpEn parameter values
Unexpected reboots or httpd process crashes on Tenda AC7 devices following inbound web requests
Outbound connections from the router to unfamiliar hosts following UPnP configuration changes
New or modified UPnP port mappings that were not initiated by an administrator

Detection Strategies

Inspect router HTTP access logs for requests to /goform/SetUpnpCfg from non-administrative source addresses
Deploy network intrusion detection signatures that flag upnpEn parameter values exceeding expected lengths
Correlate router reboot events with preceding inbound HTTP traffic to the management interface

Monitoring Recommendations

Forward router syslog and HTTP traffic metadata to a centralized SIEM or data lake for retention and analysis
Monitor for lateral movement or scanning activity originating from the router's LAN interface
Alert on any exposure of the Tenda management interface to the WAN or untrusted VLANs

How to Mitigate CVE-2025-11525

Immediate Actions Required

Restrict access to the router's web management interface to trusted management VLANs only
Disable UPnP on the Tenda AC7 if the feature is not required for the deployment
Change default and weak administrative credentials to prevent low-privilege authenticated access
Place the device behind a firewall and block external access to TCP port 80/443 of the router

Patch Information

No vendor advisory or firmware patch has been published at the time of writing. Consult the Tenda Official Website for firmware updates beyond version 15.03.06.44. If no fixed firmware is available, consider replacing affected devices with hardware that receives active security maintenance.

Workarounds

Segment the router's management plane onto a dedicated administrative network with strict ACLs
Disable remote management features and ensure the WAN-side management interface is closed
Apply MAC-based access control lists to limit which clients can reach the LAN-side web UI
Monitor for and replace end-of-life Tenda firmware where no patches are forthcoming

bash

# Example firewall rule to block external access to the router's web UI
iptables -A INPUT -i wan0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i wan0 -p tcp --dport 443 -j DROP