CVE-2025-11327: Tenda AC18 Buffer Overflow Vulnerability

CVE-2025-11327 Overview

CVE-2025-11327 is a stack-based buffer overflow vulnerability in the Tenda AC18 wireless router running firmware version 15.03.05.19(6318). The flaw exists in the /goform/SetUpnpCfg endpoint, where the upnpEn parameter is processed without proper bounds checking. Remote attackers can send a crafted HTTP request to overflow the stack buffer, potentially leading to arbitrary code execution on the device. The exploit details have been publicly disclosed, increasing the risk of opportunistic attacks against exposed devices. The vulnerability is tracked under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Critical Impact
Remote attackers with low privileges can trigger a stack-based buffer overflow to compromise the integrity, confidentiality, and availability of affected Tenda AC18 routers.

Affected Products

Tenda AC18 router (hardware)
Tenda AC18 firmware version 15.03.05.19(6318)
Devices exposing the /goform/SetUpnpCfg web management endpoint

Discovery Timeline

2025-10-06 - CVE-2025-11327 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-11327

Vulnerability Analysis

The vulnerability resides in the HTTP request handler for the /goform/SetUpnpCfg endpoint of the Tenda AC18 router's web administration interface. The handler reads the upnpEn parameter from the incoming request and copies it into a fixed-size stack buffer without validating the input length. An attacker who supplies an oversized upnpEn value can overwrite adjacent stack memory, including saved return addresses and function pointers. Successful exploitation can lead to remote code execution within the context of the router's web server process, which typically runs with elevated privileges on embedded devices.

The Exploit Prediction Scoring System assigns this CVE an EPSS score of 1.147% (62.6 percentile), indicating measurable exploitation likelihood given the public disclosure.

Root Cause

The root cause is improper restriction of operations within the bounds of a memory buffer [CWE-119]. The firmware uses unsafe string-copy operations on attacker-controlled input without enforcing length limits. Embedded MIPS-based routers like the AC18 often lack modern exploit mitigations such as stack canaries or full address-space layout randomization, making memory corruption flaws directly exploitable.

Attack Vector

The attack vector is network-based and requires authenticated low-privilege access to the router's HTTP management interface. An attacker submits a POST request to /goform/SetUpnpCfg containing an overlong upnpEn argument. Once the malformed request reaches the vulnerable handler, the oversized value corrupts the stack frame. Devices exposing the web interface to the WAN, or attackers already positioned on the LAN, can leverage this flaw to gain control of the router. Public documentation of the exploitation path is available in the GitHub IoT vulnerability report.

No verified proof-of-concept code is reproduced here. Refer to the VulDB entry #327210 and the linked GitHub write-up for technical exploitation details.

Detection Methods for CVE-2025-11327

Indicators of Compromise

HTTP POST requests to /goform/SetUpnpCfg containing abnormally long upnpEn parameter values
Unexpected reboots, crashes, or watchdog resets of the Tenda AC18 router shortly after web management traffic
Outbound connections from the router to unfamiliar hosts, indicating possible post-exploitation implant activity
New or modified UPnP port-forwarding rules that were not configured by the administrator

Detection Strategies

Inspect HTTP traffic destined for the router's management interface and flag requests where upnpEn exceeds expected length boundaries
Deploy network intrusion detection signatures that match POST requests to /goform/SetUpnpCfg with oversized parameter values
Monitor router system logs and syslog forwarding for repeated crashes of the httpd or web management process
Correlate web management access attempts with source IPs not on an administrator allowlist

Monitoring Recommendations

Forward router syslog data to a centralized log platform and alert on web service restarts or segmentation faults
Baseline normal management traffic volume and alert on bursts of POST requests to /goform/ endpoints
Continuously inventory internet-exposed Tenda AC18 devices and verify that WAN-side administration is disabled
Review firewall and IDS telemetry for scans probing UPnP configuration paths across the router fleet

How to Mitigate CVE-2025-11327

Immediate Actions Required

Disable remote (WAN-side) access to the router's web management interface until a vendor patch is available
Restrict LAN-side access to the administration interface to a small set of trusted management hosts
Disable UPnP on the router if it is not required for business operations
Change the default administrator credentials and enforce strong, unique passwords to limit low-privilege access prerequisites

Patch Information

No official vendor patch has been published in the references at the time of NVD listing. Administrators should monitor the Tenda official website for firmware updates addressing the /goform/SetUpnpCfg handler. If a fixed firmware release is published, apply it across all affected AC18 devices and validate that the management interface is no longer vulnerable to oversized upnpEn input.

Workarounds

Segment the router's management VLAN from general user networks and restrict it with ACLs
Place vulnerable AC18 devices behind an upstream firewall that inspects and length-limits HTTP parameters
Replace end-of-life or unpatched AC18 units with current-generation hardware that receives active security maintenance
Schedule periodic credential rotation for the administrative account to reduce the window for low-privilege exploitation

bash

# Example firewall rule to block WAN access to the router admin interface
# Adjust interface and address ranges to match your environment
iptables -A INPUT -i wan0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i wan0 -p tcp --dport 443 -j DROP

# Restrict LAN admin access to a single management host
iptables -A INPUT -i br-lan -s 192.0.2.10 -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -i br-lan -p tcp --dport 80 -j DROP