CVE-2025-5839 Overview
CVE-2025-5839 is a buffer overflow vulnerability in the Tenda AC9 router running firmware version 15.03.02.13. The flaw resides in the fromadvsetlanip function within /goform/AdvSetLanip, which handles POST requests for advanced LAN IP configuration. Manipulating the lanMask argument triggers a buffer overflow in the request handler. The vulnerability is exploitable remotely and has been publicly disclosed, increasing the risk of opportunistic exploitation against exposed devices.
Critical Impact
Remote attackers with low privileges can trigger memory corruption on the Tenda AC9 router, leading to potential code execution or denial of service on affected network infrastructure.
Affected Products
- Tenda AC9 router (hardware version 1.0)
- Tenda AC9 firmware version 15.03.02.13
- Devices exposing /goform/AdvSetLanip to untrusted networks
Discovery Timeline
- 2025-06-07 - CVE-2025-5839 published to NVD
- 2025-06-09 - Last updated in NVD database
Technical Details for CVE-2025-5839
Vulnerability Analysis
The vulnerability is classified under [CWE-119] as an improper restriction of operations within the bounds of a memory buffer. The flaw exists in the fromadvsetlanip function responsible for processing advanced LAN IP settings submitted through the web management interface. When the router receives a POST request to /goform/AdvSetLanip, the handler copies the user-supplied lanMask parameter into a fixed-size stack buffer without enforcing length validation. An attacker authenticated to the web interface can submit an oversized lanMask value to overwrite adjacent memory, corrupt the saved return address, and influence execution flow on the MIPS-based device.
Root Cause
The root cause is missing bounds checking on attacker-controlled input passed to an unsafe string operation inside fromadvsetlanip. The handler trusts the length of lanMask from the POST body and writes it into a stack buffer sized for a valid subnet mask string. Submitting input larger than the destination buffer overflows the stack frame.
Attack Vector
Exploitation requires network access to the router's HTTP management interface and authenticated session credentials. The attacker sends a crafted POST request to /goform/AdvSetLanip containing an oversized lanMask field. Successful exploitation can crash the httpd process or, with careful payload construction targeting the MIPS architecture, achieve arbitrary code execution as the web server user. Routers with the management interface exposed to the WAN face elevated risk.
No verified proof-of-concept code is available in trusted repositories. Refer to the Tenda AC9 fromadvsetlanip technical write-up and VulDB entry 311582 for additional details.
Detection Methods for CVE-2025-5839
Indicators of Compromise
- POST requests to /goform/AdvSetLanip containing abnormally long lanMask parameter values
- Unexpected restarts or crashes of the httpd process on Tenda AC9 devices
- Configuration changes to LAN subnet settings from unrecognized source addresses
- Outbound connections from the router to unfamiliar hosts following administrative requests
Detection Strategies
- Inspect HTTP request logs for POST bodies to /goform/AdvSetLanip exceeding expected parameter lengths
- Deploy network intrusion detection signatures that flag oversized lanMask values in Tenda management traffic
- Monitor router syslog output for repeated process crashes or watchdog-triggered reboots
- Correlate web interface authentication events with subsequent administrative configuration changes
Monitoring Recommendations
- Forward router syslog and HTTP access logs to a central log management platform for retention and analysis
- Alert on any administrative interface access originating from WAN-side IP addresses
- Track firmware version inventory across deployed Tenda devices to identify vulnerable units
How to Mitigate CVE-2025-5839
Immediate Actions Required
- Disable remote WAN management on Tenda AC9 routers running firmware 15.03.02.13
- Restrict access to the LAN management interface using ACLs limiting it to trusted administrative hosts
- Rotate administrative credentials and enforce strong passwords to reduce the risk of authenticated exploitation
- Audit routers for unexpected configuration changes and reset to known-good settings if tampering is suspected
Patch Information
No vendor patch is referenced in the published advisory at the time of NVD publication. Monitor the Tenda official website for firmware updates addressing the fromadvsetlanip handler. Where no fix is available, consider replacing affected devices with supported hardware.
Workarounds
- Place the router behind an upstream firewall and block external access to TCP port 80 and 443 of the device
- Segment the management VLAN so that only authorized administrative workstations can reach the web interface
- Disable the advanced LAN IP configuration feature if not required for the deployment
# Example upstream firewall rule blocking WAN access to the router management interface
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -i <wan_iface> -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -i <wan_iface> -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
