CVE-2025-9526: Linksys E1700 Buffer Overflow Vulnerability

CVE-2025-9526 Overview

CVE-2025-9526 is a stack-based buffer overflow vulnerability in the Linksys E1700 router running firmware version 1.0.0.4.003. The flaw resides in the setSysAdm function handler for the /goform/setSysAdm endpoint. Attackers can trigger the overflow by manipulating the rm_port argument supplied to this endpoint. The vulnerability is remotely exploitable over the network and the exploit details have been publicly disclosed. Linksys was contacted by the reporter but did not respond to the disclosure, leaving devices without a vendor-supplied patch. The 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 the router's memory through the rm_port parameter, potentially achieving arbitrary code execution on the device.

Affected Products

• Linksys E1700 hardware router
• Linksys E1700 firmware version 1.0.0.4.003
• Deployments exposing the /goform/setSysAdm administrative endpoint

Discovery Timeline

• 2025-08-27 - CVE-2025-9526 published to NVD
• 2025-10-09 - Last updated in NVD database

Technical Details for CVE-2025-9526

Vulnerability Analysis

The vulnerability exists in the setSysAdm function that processes HTTP requests sent to the /goform/setSysAdm URI on the router's web management interface. The function reads the rm_port request parameter and copies its contents into a fixed-size stack buffer without enforcing length validation. Supplying an oversized value overflows the buffer, corrupting adjacent stack memory including saved return addresses. The technical writeup published on the public GitHub research repository confirms the unsafe string handling pattern and the path to control of program flow. See the GitHub Vulnerability Documentation for the parameter trace and crash analysis.

Root Cause

The root cause is missing bounds checking on user-supplied input copied into a stack-allocated buffer. The setSysAdm handler treats the rm_port parameter as a trusted, length-bounded string and uses an unsafe copy operation. This is a classic [CWE-119] memory safety failure common in embedded MIPS/ARM web servers compiled without stack protection.

Attack Vector

The attack is delivered over the network against the device's HTTP administrative interface. An attacker authenticated with low privileges submits a crafted POST request to /goform/setSysAdm containing an oversized rm_port value. Because most consumer routers reuse default or weak admin credentials and the web interface is often reachable from the LAN, the practical barrier to exploitation is low. Successful exploitation can crash the device or, with a tailored payload, redirect execution and run attacker-controlled code with the privileges of the web server process.

No verified proof-of-concept code is reproduced here. Refer to the GitHub PoC Documentation and the VulDB #321543 entry for the disclosed exploitation details.

Detection Methods for CVE-2025-9526

Indicators of Compromise

• HTTP POST requests to /goform/setSysAdm containing unusually long rm_port parameter values
• Unexpected reboots, watchdog resets, or HTTP service crashes on Linksys E1700 devices
• Outbound connections from the router to unfamiliar IP addresses following administrative requests
• DNS or routing configuration changes that were not initiated by an administrator

Detection Strategies

• Inspect HTTP request bodies destined for the router management interface and flag rm_port values exceeding expected lengths (typically a few bytes for a port number)
• Deploy network IDS signatures that match POST requests to /goform/setSysAdm with parameter lengths beyond a sane threshold
• Correlate authentication events on the router admin interface with subsequent crash or reboot telemetry

Monitoring Recommendations

• Forward router syslog and HTTP access logs to a centralized analytics platform for anomaly review
• Monitor for repeated requests to /goform/setSysAdm from a single source, which can indicate brute-force exploitation attempts
• Baseline normal administrative traffic so that oversized parameter submissions stand out

How to Mitigate CVE-2025-9526

Immediate Actions Required

• Restrict access to the router's web administration interface to trusted management hosts on the LAN only
• Disable remote (WAN-side) administration if it is enabled on the E1700
• Change default administrative credentials and enforce a strong unique password to raise the bar for the low-privilege precondition
• Segment the router management VLAN away from untrusted user and IoT networks

Patch Information

No official Linksys patch is available at the time of publication. The vendor was contacted by the reporter but did not respond. Owners of the Linksys E1700 running firmware 1.0.0.4.003 should monitor the Linksys Official Website for future firmware updates and consider replacing the device with a supported model if no update is released.

Workarounds

• Place the router behind an upstream firewall that blocks unsolicited inbound HTTP traffic to the device
• Use ACLs on managed switches to limit which client IPs can reach the router's HTTP service
• Replace the affected E1700 with a currently supported router model if vendor silence persists
• Disable any port-forwarding rule that exposes the router admin interface to the internet

# Example: restrict router admin access to a single management host using iptables on an upstream gateway
iptables -A FORWARD -p tcp -d 192.168.1.1 --dport 80  -s 192.168.1.10 -j ACCEPT
iptables -A FORWARD -p tcp -d 192.168.1.1 --dport 443 -s 192.168.1.10 -j ACCEPT
iptables -A FORWARD -p tcp -d 192.168.1.1 --dport 80  -j DROP
iptables -A FORWARD -p tcp -d 192.168.1.1 --dport 443 -j DROP