CVE-2025-7837 Overview
CVE-2025-7837 is a buffer overflow vulnerability in the TOTOLINK T6 router running firmware version 4.1.5cu.748_B20211015. The flaw resides in the recvSlaveStaInfo function of the MQTT Service component. Attackers can trigger the overflow by manipulating the dest argument over the network. The exploit details have been publicly disclosed, increasing the risk of opportunistic exploitation against exposed devices.
Critical Impact
Remote attackers with low privileges can corrupt memory in the MQTT Service, potentially leading to arbitrary code execution and full compromise of the affected router.
Affected Products
- TOTOLINK T6 router (hardware revision 3)
- TOTOLINK T6 firmware version v4.1.5cu.748_B20211015
- MQTT Service component, recvSlaveStaInfo function
Discovery Timeline
- 2025-07-19 - CVE-2025-7837 published to NVD
- 2025-07-23 - Last updated in NVD database
Technical Details for CVE-2025-7837
Vulnerability Analysis
The vulnerability is classified under [CWE-119], improper restriction of operations within the bounds of a memory buffer. It affects the recvSlaveStaInfo function in the MQTT Service running on the TOTOLINK T6 router. The function processes incoming slave station information without validating the size of data copied into the dest buffer. An attacker who supplies an oversized value triggers a buffer overflow in the service process memory.
The attack vector is network-based and requires low privileges with no user interaction. Successful exploitation impacts confidentiality, integrity, and availability of the device. Because the exploit has been publicly disclosed, defenders should treat exposed devices as high-risk targets. The EPSS score is 0.766% at the 73rd percentile, indicating measurable exploitation interest.
Root Cause
The root cause is missing bounds checking in recvSlaveStaInfo when copying attacker-controlled input into the dest destination buffer. The MQTT Service trusts the length of incoming data without enforcing a maximum size, allowing adjacent stack or heap memory to be overwritten.
Attack Vector
An attacker reaches the MQTT Service over the network and sends crafted slave station information containing oversized payload data targeting the dest parameter. Authentication requirements are minimal, and the attack requires no user interaction. Refer to the GitHub Vulnerability Documentation and the public proof of concept for technical reproduction details.
Detection Methods for CVE-2025-7837
Indicators of Compromise
- Unexpected restarts or crashes of the MQTT Service process on TOTOLINK T6 devices
- Inbound MQTT traffic from untrusted sources targeting the router management interface
- Anomalous slave station registration messages containing oversized field values
Detection Strategies
- Inspect MQTT payloads at the network perimeter for malformed or unusually large dest fields targeting recvSlaveStaInfo
- Monitor router system logs for repeated service restarts or segmentation faults in the MQTT daemon
- Correlate network telemetry to identify scanning activity against MQTT-related ports on TOTOLINK devices
Monitoring Recommendations
- Capture and review device crash logs and syslog output for evidence of memory corruption events
- Apply network intrusion detection signatures that flag oversized MQTT control packets
- Track external references such as VulDB #316940 for updated threat intelligence on this CVE
How to Mitigate CVE-2025-7837
Immediate Actions Required
- Identify all TOTOLINK T6 devices running firmware v4.1.5cu.748_B20211015 within the environment
- Restrict network access to the MQTT Service, blocking exposure to untrusted networks and the internet
- Monitor the TOTOLINK official website for security firmware updates addressing this issue
Patch Information
No vendor patch has been documented in the available references at the time of NVD publication. Administrators should subscribe to TOTOLINK security advisories and apply firmware updates as soon as a fix is released.
Workarounds
- Place affected devices behind a firewall and deny inbound MQTT traffic from untrusted sources
- Disable the MQTT Service on the router if the feature is not required for operations
- Segment IoT and consumer-grade networking equipment away from sensitive internal networks to limit lateral movement
# Configuration example: restrict inbound traffic to the router management interface
iptables -A INPUT -p tcp --dport 1883 -s <trusted_subnet> -j ACCEPT
iptables -A INPUT -p tcp --dport 1883 -j DROP
iptables -A INPUT -p tcp --dport 8883 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
