CVE-2025-5609 Overview
CVE-2025-5609 is a buffer overflow vulnerability in the Tenda AC18 router running firmware version 15.03.05.05. The flaw resides in the fromadvsetlanip function within the /goform/AdvSetLanip endpoint. Attackers can manipulate the lanMask argument to trigger memory corruption in the affected process. The vulnerability is exploitable remotely over the network, and technical details have been publicly disclosed. The issue is tracked under [CWE-119] (improper restriction of operations within the bounds of a memory buffer) and [CWE-120] (classic buffer overflow).
Critical Impact
Remote attackers with low-privileged access can corrupt memory on the router, potentially leading to denial of service or arbitrary code execution on the device.
Affected Products
- Tenda AC18 hardware router
- Tenda AC18 firmware version 15.03.05.05
- Web management interface endpoint /goform/AdvSetLanip
Discovery Timeline
- 2025-06-04 - CVE-2025-5609 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-5609
Vulnerability Analysis
The vulnerability affects the fromadvsetlanip function in the Tenda AC18 web management binary. This function processes LAN IP configuration requests submitted through the /goform/AdvSetLanip endpoint. When a request supplies the lanMask parameter, the function copies the attacker-controlled value into a fixed-size stack or heap buffer without adequate length validation. Supplying an oversized lanMask value overflows the buffer and corrupts adjacent memory. Because the router firmware runs on an embedded Linux system without modern exploit mitigations consistently enforced, memory corruption in this code path can escalate from a service crash to full control of the router process.
Root Cause
The root cause is missing bounds checking on the lanMask HTTP request parameter before it is written into a bounded destination buffer. The handler treats untrusted input as if it conformed to the expected subnet mask format and length. No sanitization or length enforcement is applied prior to the copy operation, satisfying the conditions for both [CWE-119] and [CWE-120].
Attack Vector
Exploitation requires network reachability to the router web interface and a low-privileged authenticated session. An attacker sends a crafted HTTP POST request to /goform/AdvSetLanip with a lanMask parameter longer than the destination buffer. The oversized value triggers the overflow inside fromadvsetlanip, corrupting adjacent memory and altering control flow or crashing the service. The attack does not require user interaction. Public disclosure of the exploitation details raises the likelihood of opportunistic scanning against exposed Tenda AC18 devices. Refer to the Notion Tenda AC18 Advisory and VulDB #311095 for the disclosed reproduction details.
Detection Methods for CVE-2025-5609
Indicators of Compromise
- HTTP POST requests to /goform/AdvSetLanip containing abnormally long lanMask parameter values.
- Unexpected reboots, crashes, or restarts of the httpd process on Tenda AC18 routers.
- Outbound connections from the router to unfamiliar hosts following configuration changes.
- Unauthorized changes to LAN configuration or DNS settings on the device.
Detection Strategies
- Inspect web server and management logs on the router for repeated requests to /goform/AdvSetLanip from a single source.
- Deploy network intrusion detection signatures that flag oversized lanMask parameters in HTTP request bodies.
- Baseline router firmware version and configuration to detect unauthorized modifications.
Monitoring Recommendations
- Monitor management-plane traffic to consumer and SMB routers for unexpected external access to the web UI.
- Alert on repeated authentication attempts against the Tenda AC18 admin interface.
- Track HTTP request payload sizes for /goform/* endpoints and flag statistical outliers.
How to Mitigate CVE-2025-5609
Immediate Actions Required
- Restrict access to the router web management interface to trusted LAN hosts only and disable remote WAN administration.
- Rotate the router administrator password to invalidate any previously captured low-privilege credentials.
- Isolate exposed Tenda AC18 devices behind an upstream firewall until a vendor fix is available.
- Audit LAN and DNS settings on affected devices for unauthorized modifications.
Patch Information
At the time of publication, no vendor patch has been referenced in the disclosure. Consult the Tenda Official Website for firmware updates and advisories related to the AC18 platform. If a newer firmware release becomes available for the AC18, apply it after verifying integrity and compatibility.
Workarounds
- Disable the web management interface on the WAN side and permit administration only from a dedicated management VLAN.
- Place the router behind a network access control policy that filters HTTP requests to /goform/AdvSetLanip from untrusted sources.
- Replace end-of-life or unsupported Tenda AC18 devices with actively maintained hardware in production networks.
# Example iptables rule restricting router admin access to a trusted subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.10.0/24 -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.
