CVE-2025-7913: Totolink T6 Buffer Overflow Vulnerability

CVE-2025-7913 Overview

CVE-2025-7913 is a buffer overflow vulnerability in the TOTOLINK T6 router running firmware version 4.1.5cu.748_B20211015. The flaw resides in the updateWifiInfo function of the MQTT Service component. Attackers manipulate the serverIp argument to trigger memory corruption on the device. The vulnerability is exploitable remotely over the network and a public exploit disclosure exists. 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 trigger a buffer overflow in the MQTT Service, potentially leading to arbitrary code execution or denial of service on affected TOTOLINK T6 routers.

Affected Products

TOTOLINK T6 router (hardware revision 3)
TOTOLINK T6 firmware version 4.1.5cu.748_B20211015
MQTT Service component containing the updateWifiInfo function

Discovery Timeline

2025-07-21 - CVE-2025-7913 published to NVD
2025-07-23 - Last updated in NVD database

Technical Details for CVE-2025-7913

Vulnerability Analysis

The vulnerability exists in the updateWifiInfo function exposed through the MQTT Service running on the TOTOLINK T6. When the function processes the serverIp argument, it copies attacker-supplied data into a fixed-size memory buffer without enforcing length validation. This violates safe memory boundary handling as defined by [CWE-119].

Because the affected component is the MQTT Service, the attack surface is reachable over the network. An attacker who can deliver a crafted MQTT message containing an oversized serverIp value can overwrite adjacent memory regions in the device process. Depending on the memory layout and mitigations present on the embedded platform, exploitation can corrupt control flow and lead to arbitrary code execution on the router. Public disclosure of the vulnerability details on GitHub increases the likelihood of weaponization.

Root Cause

The root cause is missing input length validation on the serverIp parameter inside the updateWifiInfo handler. The function trusts the size of the input string and writes it into a fixed-length stack or heap buffer. Without bounds checks, oversized values overflow the destination buffer and corrupt adjacent memory.

Attack Vector

The attack vector is network-based and requires low privileges. An attacker sends a crafted message to the MQTT Service supplying an oversized serverIp argument to the updateWifiInfo function. Successful exploitation requires no user interaction. Refer to the published proof-of-concept for technical details on the message structure and triggering conditions.

Detection Methods for CVE-2025-7913

Indicators of Compromise

Unexpected crashes, restarts, or watchdog resets of the MQTT Service process on TOTOLINK T6 routers
Inbound MQTT connections from untrusted external sources to the device management interface
MQTT payloads containing abnormally long serverIp field values
Unexplained modifications to Wi-Fi configuration or MQTT broker settings on the device

Detection Strategies

Inspect MQTT traffic for messages targeting the updateWifiInfo handler and validate serverIp field length against expected IPv4/hostname formats
Monitor router logs for repeated service crashes or restart events correlated with MQTT activity
Deploy network IDS signatures to flag MQTT packets containing oversized string arguments destined for embedded devices

Monitoring Recommendations

Restrict and log all inbound traffic to MQTT ports (typically 1883 and 8883) at the network perimeter
Track firmware version inventory for TOTOLINK T6 devices to identify systems running 4.1.5cu.748_B20211015
Alert on outbound connections from router management subnets to unknown destinations following MQTT activity

How to Mitigate CVE-2025-7913

Immediate Actions Required

Block external network access to the MQTT Service on affected TOTOLINK T6 devices using upstream firewall rules
Disable the MQTT Service on the router if it is not required for operation
Place affected routers behind a segmented management network with strict access control lists
Inventory all TOTOLINK T6 deployments and identify devices running firmware 4.1.5cu.748_B20211015

Patch Information

No vendor advisory or fixed firmware version has been published at the time of NVD publication. Monitor the TOTOLINK official website for updated firmware releases addressing CVE-2025-7913. Additional tracking information is available via VulDB entry #317028.

Workarounds

Disable the MQTT Service in the device configuration if the deployment does not require it
Filter inbound MQTT traffic at the network boundary to permit only trusted broker addresses
Replace end-of-life or unpatched TOTOLINK T6 units with currently supported router models

bash

# Example: block external access to MQTT ports upstream of the router
iptables -A FORWARD -p tcp --dport 1883 -j DROP
iptables -A FORWARD -p tcp --dport 8883 -j DROP