CVE-2025-9527: Linksys E1700 Buffer Overflow Vulnerability

CVE-2025-9527 Overview

CVE-2025-9527 is a stack-based buffer overflow in the Linksys E1700 wireless router running firmware version 1.0.0.4.003. The flaw resides in the QoSSetup function within the /goform/QoSSetup endpoint of the device's web management interface. Attackers can trigger the overflow by manipulating the ack_policy argument in HTTP requests sent to the router. The vulnerability is exploitable over the network and has been publicly disclosed, including a proof-of-concept. According to the disclosure, the vendor was contacted but did not respond. The weakness is tracked under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Critical Impact

Remote attackers with low-privilege access to the router's management interface can corrupt stack memory, potentially leading to arbitrary code execution on the device.

Affected Products

• Linksys E1700 router (hardware)
• Linksys E1700 firmware version 1.0.0.4.003
• Deployments exposing the /goform/QoSSetup endpoint over LAN or WAN

Discovery Timeline

• 2025-08-27 - CVE-2025-9527 published to NVD
• 2025-10-09 - Last updated in NVD database

Technical Details for CVE-2025-9527

Vulnerability Analysis

The vulnerability exists in the QoSSetup handler that processes Quality of Service configuration requests submitted to /goform/QoSSetup. The handler reads the ack_policy parameter from an HTTP request and copies it into a fixed-size stack buffer without validating the input length. Supplying an oversized value overflows the buffer and overwrites adjacent stack data, including saved return addresses.

Linksys E1700 firmware is built on a MIPS-based embedded Linux platform with web management binaries that typically lack modern exploit mitigations such as stack canaries, full ASLR, and non-executable stacks. This increases the likelihood that an overflow can be converted into reliable code execution. The exploit details and a proof-of-concept have been published on the GitHub Vulnerability Summary and indexed in VulDB #321544.

Root Cause

The root cause is missing bounds checking on user-supplied input. The QoSSetup function copies the ack_policy argument into a stack-allocated buffer using an unsafe string operation, with no length check against the destination size. This matches the [CWE-119] pattern of improper restriction of operations within the bounds of a memory buffer.

Attack Vector

The attack is network-based and requires authenticated access to the router's web interface. An attacker submits a crafted POST request to /goform/QoSSetup with an ack_policy value long enough to overflow the destination buffer. Successful exploitation can crash the httpd process, cause a denial of service, or in a fully developed exploit, redirect execution to attacker-controlled shellcode. Routers exposing the management interface to the WAN are at higher risk, particularly where default or weak credentials remain in use.

No verified exploitation code is reproduced here. Technical details and a proof-of-concept are available in the GitHub PoC Repository.

Detection Methods for CVE-2025-9527

Indicators of Compromise

• HTTP POST requests to /goform/QoSSetup containing unusually long ack_policy parameter values
• Repeated crashes or restarts of the router's httpd web management process
• Unexpected configuration changes to QoS settings or new administrative sessions from unfamiliar source addresses
• Outbound connections from the router to unknown hosts following management interface activity

Detection Strategies

• Inspect web server and management interface logs for malformed or oversized form parameters submitted to /goform/ endpoints
• Deploy network IDS signatures that flag POST bodies to /goform/QoSSetup exceeding expected ack_policy field length
• Monitor for repeated authentication followed by anomalous POST requests to QoS configuration endpoints

Monitoring Recommendations

• Forward router syslog and HTTP access logs to a centralized logging platform for correlation
• Alert on router reboots, watchdog restarts, or httpd segmentation faults that may indicate exploitation attempts
• Track changes to administrative accounts, DNS settings, and firmware on edge devices that may follow a successful compromise

How to Mitigate CVE-2025-9527

Immediate Actions Required

• Disable remote (WAN-side) administration on the Linksys E1700 if enabled
• Restrict access to the router's web management interface to a small set of trusted LAN hosts
• Replace any default or weak administrator credentials with strong, unique passwords
• Inventory affected devices and plan replacement, since the vendor has not responded to disclosure

Patch Information

No vendor patch has been released for CVE-2025-9527 as of the last NVD update on 2025-10-09. The disclosure record states the vendor was contacted early but did not respond. Organizations should treat affected E1700 units as unpatched and consider migrating to a supported router platform that receives current security updates.

Workarounds

• Place the router behind a network segment that blocks untrusted access to TCP port 80/443 on the device
• Use firewall rules to restrict source IPs permitted to reach the /goform/QoSSetup endpoint
• Disable the QoS feature in the web UI if the underlying handler is not invoked when the feature is off, reducing the attack surface
• Replace the device with vendor-supported hardware if continued use of the E1700 is not feasible

# Example: restrict router management to a single admin workstation using an upstream firewall
# Replace 192.0.2.10 with the admin host and 192.0.2.1 with the router IP
iptables -I FORWARD -s 192.0.2.10 -d 192.0.2.1 -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -d 192.0.2.1 -p tcp --dport 80 -j DROP
iptables -I FORWARD -d 192.0.2.1 -p tcp --dport 443 -j DROP