CVE-2025-6113 Overview
CVE-2025-6113 is a buffer overflow vulnerability in the Tenda FH1203 router running firmware version 2.0.1.6. The flaw resides in the fromadvsetlanip function within /goform/AdvSetLanip. Attackers can trigger memory corruption by manipulating the lanMask argument. The vulnerability is exploitable remotely over the network and the exploit details have been publicly disclosed. The underlying weakness is classified as [CWE-119], improper restriction of operations within the bounds of a memory buffer.
Critical Impact
Remote attackers with low-level privileges can corrupt memory on affected Tenda FH1203 devices, potentially leading to arbitrary code execution or denial of service against the router.
Affected Products
- Tenda FH1203 router (hardware)
- Tenda FH1203 firmware version 2.0.1.6
- Deployments exposing the /goform/AdvSetLanip administrative endpoint
Discovery Timeline
- 2025-06-16 - CVE-2025-6113 published to NVD
- 2025-06-17 - Last updated in NVD database
Technical Details for CVE-2025-6113
Vulnerability Analysis
The vulnerability affects the fromadvsetlanip handler exposed through the /goform/AdvSetLanip web interface on the Tenda FH1203 router. This endpoint processes LAN IP configuration requests submitted by authenticated users. The function processes the lanMask parameter without enforcing proper bounds on the supplied input. An attacker who can reach the router's management interface can submit a crafted lanMask value that overflows a fixed-size buffer.
Memory corruption in embedded router firmware typically leads to crashes, watchdog reboots, or arbitrary code execution within the context of the web server process. Tenda devices commonly run web management daemons with elevated privileges, so successful exploitation can yield control over the router's traffic flow, DNS resolution, and inter-network routing.
Root Cause
The root cause is the absence of length validation on the lanMask argument before it is copied into a fixed-size stack or heap buffer inside fromadvsetlanip. This pattern, classified as [CWE-119], is recurrent across Tenda's goform handlers, where user-controlled HTTP parameters are passed directly to unsafe string operations such as strcpy or sprintf.
Attack Vector
Exploitation requires network access to the router's management interface and a low-privilege authenticated session. An attacker sends an HTTP POST request to /goform/AdvSetLanip containing an oversized lanMask value. The malformed input overruns the destination buffer, overwriting adjacent memory structures including saved return addresses or function pointers. Public technical details are available in the Notion writeup for Tenda FH1203 and the VulDB Entry #312582.
No verified proof-of-concept code is published in vendor advisories. Refer to the linked third-party references for technical reproduction details.
Detection Methods for CVE-2025-6113
Indicators of Compromise
- HTTP POST requests to /goform/AdvSetLanip containing abnormally long lanMask parameter values
- Unexpected reboots or crashes of the Tenda FH1203 web management daemon
- Unauthorized changes to LAN subnet configuration, DHCP scope, or DNS settings on the router
- Outbound connections from the router to unknown command-and-control infrastructure following configuration changes
Detection Strategies
- Inspect HTTP traffic destined for router management interfaces and alert on lanMask parameter values exceeding expected length for IPv4 subnet masks
- Baseline firmware version and configuration state, then alert on unexpected drift on Tenda FH1203 devices
- Correlate router crash events with preceding HTTP POSTs to goform endpoints in network logs
Monitoring Recommendations
- Forward router syslog and web access logs to a central SIEM for retention and correlation
- Monitor administrative web interfaces of all SOHO routers for anomalous POST request sizes and parameter lengths
- Track devices that expose management interfaces to untrusted network segments or the internet
How to Mitigate CVE-2025-6113
Immediate Actions Required
- Restrict access to the Tenda FH1203 management interface to trusted LAN hosts only, blocking WAN-side administrative access
- Rotate administrative credentials and disable any unused remote management features
- Place affected devices behind a network firewall that filters HTTP requests to /goform/AdvSetLanip from untrusted sources
- Inventory all Tenda FH1203 routers running firmware 2.0.1.6 and prioritize remediation
Patch Information
At the time of NVD publication on 2025-06-16, no vendor advisory or security patch from Tenda is referenced in the CVE entry. Consult the Tenda official website for firmware updates and check for newer releases that supersede version 2.0.1.6. If no patched firmware is available, plan for device replacement or compensating network controls.
Workarounds
- Disable remote (WAN) management on the router and enforce administrative access from a dedicated management VLAN
- Apply ACLs upstream of the router to drop HTTP requests targeting /goform/AdvSetLanip from unauthorized sources
- Replace end-of-support or unpatchable Tenda FH1203 units with hardware that receives active security maintenance
# Example iptables rule to restrict access to the router management interface
# Replace 192.168.1.0/24 with your trusted management network
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
