CVE-2025-9525: Linksys E1700 Buffer Overflow Vulnerability

CVE-2025-9525 Overview

CVE-2025-9525 is a stack-based buffer overflow vulnerability in the Linksys E1700 wireless router running firmware version 1.0.0.4.003. The flaw resides in the setWan function within the /goform/setWan endpoint. Attackers can trigger the overflow by manipulating the DeviceName or lanIp arguments. The vulnerability is remotely exploitable and a public proof-of-concept has been published. According to the disclosure, the vendor was contacted prior to publication but did not respond. The weakness is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Critical Impact
Remote attackers with low privileges can corrupt stack memory on the router, enabling arbitrary code execution or denial of service against the device.

Affected Products

Linksys E1700 hardware router
Linksys E1700 Firmware version 1.0.0.4.003
Deployments exposing the web management interface (/goform/setWan)

Discovery Timeline

2025-08-27 - CVE-2025-9525 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-9525

Vulnerability Analysis

The vulnerability stems from unsafe handling of user-supplied input inside the setWan function exposed at /goform/setWan on the Linksys E1700 router web interface. The function processes WAN configuration parameters submitted by authenticated users, including DeviceName and lanIp. Neither parameter undergoes adequate length validation before being copied into a fixed-size stack buffer. This produces a classic stack-based buffer overflow that overwrites adjacent stack data, including saved return addresses.

Successful exploitation allows attackers to overwrite control flow data on the stack. On embedded MIPS-based Linksys devices, this typically leads to arbitrary code execution in the context of the web server process, which runs with elevated privileges on the router. The attack is launched over the network and requires only low-privilege access to the management interface.

Root Cause

The root cause is the absence of bounds checking when copying the DeviceName and lanIp HTTP form parameters into stack-allocated buffers within the setWan handler. The firmware lacks stack protection mechanisms such as canaries or address space layout randomization, which makes exploitation reliable.

Attack Vector

An attacker sends a crafted HTTP POST request to /goform/setWan containing an oversized DeviceName or lanIp value. The request must reach the router's management interface, which is typically exposed on the LAN but can also be reachable from the WAN if remote administration is enabled. Public proof-of-concept code documenting the request structure has been published on GitHub.

The vulnerability manifests during string copy operations in the setWan handler. See the GitHub Vulnerability Documentation and the GitHub PoC for technical details.

Detection Methods for CVE-2025-9525

Indicators of Compromise

HTTP POST requests to /goform/setWan containing abnormally long DeviceName or lanIp parameter values
Unexpected reboots or web service crashes on the Linksys E1700 router
Unauthorized changes to WAN configuration or DNS settings on the device
Outbound connections from the router to unfamiliar hosts indicating implant activity

Detection Strategies

Inspect inbound traffic to router management interfaces for oversized form-data parameters using network IDS signatures
Monitor router syslog output for httpd or web service segmentation faults and process restarts
Compare current router firmware versions against the affected version 1.0.0.4.003 during asset inventory scans

Monitoring Recommendations

Forward router syslog and SNMP trap data to a centralized logging platform for anomaly review
Alert on configuration changes to WAN, DNS, and administrative credentials on edge networking devices
Track HTTP request sizes targeting /goform/ endpoints across managed network equipment

How to Mitigate CVE-2025-9525

Immediate Actions Required

Disable remote administration on the Linksys E1700 to limit exposure to LAN-only attackers
Restrict access to the web management interface to a dedicated management VLAN or trusted host range
Rotate router administrative credentials and disable unused services on the device
Plan migration to a supported router model, as the Linksys E1700 is an end-of-life device

Patch Information

No vendor patch is available. According to the disclosure, Linksys was contacted prior to public release but did not respond. Refer to the Linksys Official Website for any future firmware updates and the VulDB entry #321542 for tracking status.

Workarounds

Place the router behind a network firewall that blocks untrusted access to TCP port 80/443 on the device
Disable the web administration interface when not actively performing configuration changes
Replace the affected device with a currently supported router that receives security updates

bash

# Configuration example: restrict management interface access at an upstream firewall
# Allow only a trusted management host to reach the router's web UI
iptables -A FORWARD -s 192.0.2.10 -d <router_ip> -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP