CVE-2025-3993 Overview
CVE-2025-3993 is a buffer overflow vulnerability in the TOTOLINK N150RT wireless router running firmware version 3.4.0-B20190525. The flaw resides in the /boafrm/formWsc endpoint, where the submit-url argument is processed without proper bounds checking. Attackers can trigger memory corruption by submitting an oversized value for this parameter. The vulnerability is remotely exploitable over the network and the exploit has been publicly disclosed. Successful exploitation can lead to denial of service or arbitrary code execution on the embedded device.
Critical Impact
A remote attacker with low privileges can corrupt memory in the router's web management interface, potentially achieving code execution on the device and gaining a foothold inside the network perimeter.
Affected Products
- TOTOLINK N150RT router (hardware version 2.0)
- TOTOLINK N150RT firmware version 3.4.0-B20190525
- Devices exposing the /boafrm/formWsc web interface endpoint
Discovery Timeline
- 2025-04-28 - CVE-2025-3993 published to the National Vulnerability Database
- 2025-05-12 - Last updated in NVD database
Technical Details for CVE-2025-3993
Vulnerability Analysis
The vulnerability lives in the HTTP request handler for /boafrm/formWsc, a Boa web server form processor used by the N150RT firmware for Wi-Fi Protected Setup (WPS) configuration. The handler reads the submit-url POST parameter into a fixed-size stack or static buffer without validating the length of attacker-supplied input. Submitting an overly long submit-url value overflows the buffer and overwrites adjacent memory.
The weakness is categorized under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer) and [CWE-120] (Classic Buffer Overflow). On the MIPS-based embedded environment typical of TOTOLINK devices, attackers can leverage the overflow to overwrite saved return addresses or function pointers and redirect execution. The EPSS probability is 0.558% with a percentile of 68.5, indicating moderate exploitation likelihood relative to other CVEs.
Root Cause
The Boa-derived web server in the N150RT firmware copies the submit-url form value into a destination buffer using an unsafe string operation, such as strcpy or sprintf, with no length check against the buffer size. The firmware does not enforce input sanitization or maximum length on the parameter before the copy occurs.
Attack Vector
An attacker reachable on the network sends a crafted HTTP POST request to /boafrm/formWsc containing an oversized submit-url parameter. Exploitation requires authentication to the router's web interface (the CVSS vector specifies PR:L), so an attacker needs either valid credentials, default credentials, or access to a session. After authentication, the request triggers the overflow and can be used to crash the device or execute attacker-controlled code in the context of the web server process, which typically runs as root on consumer router firmware.
No verified public exploit code is referenced in NVD beyond a proof-of-concept disclosure hosted on GitHub. See the GitHub PoC Repository and VulDB entry #306329 for additional technical context.
Detection Methods for CVE-2025-3993
Indicators of Compromise
- HTTP POST requests to /boafrm/formWsc containing abnormally long submit-url parameter values, often exceeding several hundred bytes.
- Unexpected reboots, web interface crashes, or httpd process restarts on the N150RT router.
- Outbound connections from the router to unfamiliar hosts following suspicious management-interface traffic.
Detection Strategies
- Inspect web traffic destined for router management interfaces and alert on POST requests to /boafrm/formWsc with parameter lengths above a sane threshold.
- Correlate authentication events on the router with subsequent malformed requests to WPS configuration endpoints.
- Monitor for non-printable characters or shellcode-like byte patterns in HTTP form fields targeting embedded devices.
Monitoring Recommendations
- Capture router syslog output to a central log store and alert on httpd crash signatures or watchdog reboots.
- Place an IDS sensor on the LAN segment hosting management traffic and load signatures for oversized parameters in Boa-based form handlers.
- Track configuration changes on the N150RT and flag unauthorized modifications to admin credentials, DNS settings, or firmware images.
How to Mitigate CVE-2025-3993
Immediate Actions Required
- Restrict access to the router's web administration interface to trusted management hosts and disable remote (WAN-side) administration.
- Replace default and weak administrator credentials with strong, unique passwords to raise the bar for the required PR:L access.
- Segment the N150RT from sensitive internal assets and treat the device as untrusted until vendor patches are confirmed.
Patch Information
At the time of NVD publication and last modification, no vendor advisory or firmware update has been published by TOTOLINK addressing CVE-2025-3993. The N150RT firmware version 3.4.0-B20190525 remains affected. Check the TOTOLINK official website for firmware releases and replace the device if it has reached end-of-support.
Workarounds
- Disable WPS functionality on the router to reduce exposure of the affected formWsc handler.
- Block external access to TCP ports used by the web management interface at the upstream firewall or ISP gateway.
- Replace end-of-life consumer routers with current models that receive active security maintenance.
# Example: block external access to the router management interface
# Apply on an upstream firewall (replace ROUTER_IP and MGMT_PORT as appropriate)
iptables -A FORWARD -d ROUTER_IP -p tcp --dport MGMT_PORT -i WAN_IFACE -j DROP
# Restrict management access to a single trusted admin host on the LAN
iptables -A FORWARD -d ROUTER_IP -p tcp --dport MGMT_PORT -s TRUSTED_ADMIN_IP -j ACCEPT
iptables -A FORWARD -d ROUTER_IP -p tcp --dport MGMT_PORT -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
