CVE-2025-3346: Tenda AC7 Buffer Overflow Vulnerability

CVE-2025-3346 Overview

CVE-2025-3346 is a buffer overflow vulnerability in the Tenda AC7 wireless router running firmware version 15.03.06.44. The flaw resides in the formSetPPTPServer function handling requests to /goform/SetPptpServerCfg. Attackers can trigger the overflow by manipulating the pptp_server_start_ip and pptp_server_end_ip parameters. The vulnerability is exploitable remotely and a public proof-of-concept has been disclosed.

The issue maps to [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer) and [CWE-120] (Classic Buffer Overflow). Successful exploitation can corrupt router memory and potentially enable arbitrary code execution on the device.

Critical Impact
Remote attackers with low privileges can corrupt memory on affected Tenda AC7 routers through the PPTP server configuration endpoint, leading to denial of service or potential code execution on a network edge device.

Affected Products

Tenda AC7 router (hardware)
Tenda AC7 firmware version 15.03.06.44
Web management interface endpoint /goform/SetPptpServerCfg

Discovery Timeline

2025-04-07 - CVE-2025-3346 published to NVD
2025-05-27 - Last updated in NVD database

Technical Details for CVE-2025-3346

Vulnerability Analysis

The vulnerability exists in the formSetPPTPServer function, which processes PPTP (Point-to-Point Tunneling Protocol) server configuration submitted through the router's web administration interface. When a client posts to /goform/SetPptpServerCfg, the handler reads the pptp_server_start_ip and pptp_server_end_ip parameters from the request and copies them into fixed-size stack buffers without validating input length.

Because the copy operation does not enforce a maximum size, oversized values overwrite adjacent stack memory, including saved return addresses. On MIPS-based Tenda firmware, controlling the return address typically allows redirection of execution flow.

Root Cause

The root cause is missing bounds checking on user-controlled input prior to a string copy operation. The handler trusts attacker-supplied form fields and uses unsafe copy primitives such as strcpy or sprintf against stack-allocated buffers, a recurring pattern across Tenda router firmware.

Attack Vector

Exploitation requires network access to the router's HTTP management interface and authenticated access at low privilege. An attacker submits a crafted POST request to /goform/SetPptpServerCfg with overlong values for the IP range parameters. The malformed payload overflows the destination buffer and overwrites control flow data on the stack.

Public technical details and reproduction steps are available in the GitHub PoC writeup and the VulDB entry.

Detection Methods for CVE-2025-3346

Indicators of Compromise

HTTP POST requests to /goform/SetPptpServerCfg containing abnormally long pptp_server_start_ip or pptp_server_end_ip parameter values.
Unexpected reboots, crashes, or httpd process restarts on Tenda AC7 routers following web management activity.
Outbound connections originating from the router to unfamiliar hosts, indicating possible post-exploitation activity.

Detection Strategies

Inspect web server and router logs for malformed PPTP configuration submissions, particularly parameters exceeding typical IPv4 address length (15 characters).
Deploy network IDS signatures that flag POST requests to /goform/SetPptpServerCfg with parameter values exceeding a sane threshold.
Monitor for repeated authentication attempts followed by configuration changes to the PPTP server endpoint.

Monitoring Recommendations

Forward router syslog data to a centralized logging platform and alert on httpd crashes or watchdog-triggered reboots.
Baseline normal administrative activity on the router and alert on out-of-hours configuration changes.
Restrict and audit access to the router's LAN-side management interface using network segmentation.

How to Mitigate CVE-2025-3346

Immediate Actions Required

Disable remote management on the WAN interface of Tenda AC7 devices and restrict LAN-side management to trusted administrative hosts.
Disable the PPTP server feature if it is not actively used in the environment.
Rotate router administrative credentials and enforce strong, unique passwords to limit access to the vulnerable endpoint.

Patch Information

At the time of publication, no vendor patch has been referenced in the NVD entry for Tenda AC7 firmware 15.03.06.44. Administrators should monitor the Tenda official website for firmware updates addressing CVE-2025-3346. Where feasible, replace end-of-support consumer routers with actively maintained hardware that receives timely security updates.

Workarounds

Place the router management interface behind a firewall ACL that permits only specific administrative IP addresses.
Disable the PPTP server functionality via the web UI to remove the vulnerable code path from normal request handling.
Segment the router from sensitive internal networks so a compromised device cannot pivot directly to critical assets.

bash

# Example: block external access to the Tenda web management interface upstream
iptables -A FORWARD -p tcp --dport 80 -d <router-lan-ip> -s <trusted-admin-subnet> -j ACCEPT
iptables -A FORWARD -p tcp --dport 80 -d <router-lan-ip> -j DROP
iptables -A FORWARD -p tcp --dport 443 -d <router-lan-ip> -s <trusted-admin-subnet> -j ACCEPT
iptables -A FORWARD -p tcp --dport 443 -d <router-lan-ip> -j DROP