CVE-2025-6627: Totolink A702r Buffer Overflow Vulnerability

CVE-2025-6627 Overview

CVE-2025-6627 is a buffer overflow vulnerability in the TOTOLINK A702R router firmware version 4.0.0-B20230721.1521. The flaw resides in the HTTP POST request handler that processes requests to /boafrm/formIpv6Setup. Attackers manipulate the submit-url argument to trigger memory corruption in the router's web management interface. The vulnerability is exploitable remotely across the network and requires only low privileges. Public disclosure has occurred, and proof-of-concept details are available through community references. The weakness is tracked under CWE-119 (improper restriction of operations within memory buffer bounds).

Critical Impact
Remote attackers with low privileges can trigger a buffer overflow that compromises the router's confidentiality, integrity, and availability, potentially enabling arbitrary code execution on the embedded device.

Affected Products

TOTOLINK A702R hardware router
TOTOLINK A702R firmware version 4.0.0-B20230721.1521
Deployments exposing the router web management interface over the network

Discovery Timeline

2025-06-25 - CVE-2025-6627 published to NVD
2025-07-16 - Last updated in NVD database

Technical Details for CVE-2025-6627

Vulnerability Analysis

The vulnerability lives inside the boa HTTP server binary that TOTOLINK uses for device administration. When the router receives a POST request to the endpoint /boafrm/formIpv6Setup, the handler reads the submit-url parameter from the request body. The handler copies the attacker-controlled value into a fixed-size stack or heap buffer without enforcing a length check. Supplying an oversized submit-url value overruns adjacent memory, corrupting saved return addresses, function pointers, or control structures. The exploit requires authentication at a low privilege level but no user interaction, and the attack originates over the network. EPSS data places the exploitation probability in the 86th percentile, indicating elevated likelihood of in-the-wild abuse against unpatched devices.

Root Cause

The root cause is missing input length validation on the submit-url POST parameter inside the formIpv6Setup handler. The handler relies on unsafe string copy semantics typical of strcpy or sprintf patterns common in BOA-derived embedded HTTP servers. No bounds check exists between the attacker-supplied buffer size and the destination buffer allocation, classifying the issue under [CWE-119].

Attack Vector

An authenticated remote attacker sends a crafted HTTP POST request to the router's management interface targeting /boafrm/formIpv6Setup. The request body includes a submit-url field containing a payload longer than the destination buffer. The overflow can crash the device, causing denial of service, or be shaped to hijack control flow and execute arbitrary code with the privileges of the web server process. Routers exposing the management interface to the WAN broaden the attack surface considerably.

No verified exploit code is published in this article. Refer to the GitHub CVE Discussion and VulDB #313852 Details for technical write-ups.

Detection Methods for CVE-2025-6627

Indicators of Compromise

HTTP POST requests to /boafrm/formIpv6Setup containing abnormally long submit-url parameter values
Unexpected reboots, crashes, or watchdog resets of TOTOLINK A702R devices
New outbound connections from the router to unknown infrastructure following web-interface activity
Configuration changes to IPv6 settings that do not correspond to administrator actions

Detection Strategies

Inspect web traffic destined for router management interfaces and alert on POST bodies where submit-url exceeds expected length thresholds
Deploy network IDS signatures that flag requests to /boafrm/formIpv6Setup containing non-URL byte patterns or shellcode-like sequences
Correlate router log anomalies, such as repeated authentication followed by service restarts, with upstream firewall telemetry

Monitoring Recommendations

Forward router syslog and HTTP access logs to a centralized analytics platform for retention and search
Baseline normal administrative request sizes and alert on outliers targeting formIpv6Setup or similar endpoints
Monitor for management-plane exposure to the WAN using external attack surface scans

How to Mitigate CVE-2025-6627

Immediate Actions Required

Restrict access to the router's web management interface to trusted LAN segments and disable WAN-side administration
Rotate administrator credentials for any TOTOLINK A702R device that may have been exposed to untrusted networks
Audit recent device configurations for unauthorized changes to IPv6 and routing settings
Isolate affected devices behind upstream firewalls that filter requests to /boafrm/formIpv6Setup

Patch Information

At the time of publication, TOTOLINK has not released a vendor advisory or firmware update specifically referencing CVE-2025-6627. Check the Totolink Security Page for updated firmware releases and replace 4.0.0-B20230721.1521 once a fixed version is available.

Workarounds

Disable remote management on the WAN interface in the router administration panel
Apply ACLs on upstream network equipment to block external HTTP and HTTPS access to the router's management ports
Place the router behind a network appliance capable of inspecting and filtering HTTP POST payloads to /boafrm/formIpv6Setup
Consider replacing end-of-life or unsupported TOTOLINK A702R units with actively maintained hardware

bash

# Example upstream firewall rule (iptables) blocking external access to router admin
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 80 ! -s 192.168.0.0/16 -j DROP
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 443 ! -s 192.168.0.0/16 -j DROP