Introduction
Remote attackers can take full control of Linksys E1700 routers running firmware 1.0.0.4.003 by exploiting a stack-based buffer overflow in the device's web interface. The vulnerability, CVE-2025-9527, is being actively discussed in the security community because public exploits are available and the vendor has not responded. For organizations and individuals that rely on the Linksys E1700 for network connectivity, it leaves critical infrastructure open to remote code execution.
About Linksys: Linksys makes consumer and small-business networking hardware and has millions of devices deployed globally. Its product line includes routers, range extenders, and mesh systems. The E1700 is a value-focused wireless router popular in homes and small offices. Linksys has had repeated security problems in recent years, with several buffer overflow vulnerabilities reported in 2025 alone.
Technical Information
CVE-2025-9527 is a stack-based buffer overflow in the QoSSetup function of Linksys E1700 firmware version 1.0.0.4.003. It is triggered when the router's web interface receives a crafted HTTP POST request to /goform/QoSSetup with an oversized ack_policy parameter. The firmware does not check the length of this parameter before copying it into a stack-allocated buffer, so the copy corrupts memory on the stack.
A remote attacker can overwrite the return address or other control data on the stack and may achieve arbitrary code execution with the privileges of the web server process. The flaw resembles other Linksys buffer overflows from 2025, such as CVE-2025-9392 and CVE-2025-9393, which also come from insufficient input validation in web interface functions. The affected firmware does not implement modern exploit mitigations like stack canaries or ASLR, which makes exploitation easier.
Linksys has not released an official patch as of the publication date, and it has not responded to coordinated disclosure attempts.
Proof of Concept
The proof of concept (PoC) shows how an attacker can use the NTP configuration interface of the affected Linksys devices to execute arbitrary commands. By manipulating NTP configuration parameters such as manual_year_select, manual_month_select, manual_day_select, manual_hour_select, manual_min_select, and manual_sec_select, an attacker can inject and execute OS commands.
The attacker sends a crafted HTTP request to the /goform/NTP endpoint with malicious payloads in these parameters. The device processes the input without proper validation and executes the injected commands. A remote attacker can use this to gain unauthorized access and potentially take full control of the device.
The PoC gives a clear method for exploitation, but running these attacks without authorization is illegal and unethical. This information is intended only for education and for developing appropriate security measures.
PoC Reference: https://github.com/advisories/ghsa-mv4p-726j-2pc3
Detection Methods
Detecting vulnerabilities in network devices like the Linksys E8450 v1.2.00.360516 takes several methods used together. The provided sources do not describe detection methods for this particular vulnerability, so the strategies below are general ones for finding issues of this kind:
1. Network Traffic Analysis:
Unusual traffic patterns can reveal exploitation attempts. Unexpected outbound connections or irregular data flows, for instance, may indicate a compromise. Zeek (formerly Bro) is a good tool for this work. For CVE-2020-16898, dedicated Zeek scripts were written to identify malicious activity associated with that vulnerability. (github.com)
2. Log File Examination:
Review system and application logs regularly for signs of unauthorized access or configuration changes. Look for anomalies such as failed login attempts, changes to system files, or unexpected system reboots.
3. Vulnerability Scanning:
Scan devices for known vulnerabilities with automated tools. These scanners compare device configurations against databases of known issues and flag potential security gaps.
4. Firmware Integrity Checks:
Verify device firmware regularly against the checksums or cryptographic hashes the vendor provides. A match confirms that no unauthorized modifications have occurred.
5. Behavioral Analysis:
Systems that monitor device behavior for deviations from the norm can be effective. If a router begins communicating with unfamiliar external servers, for example, it may have been compromised.
Detection Reference: https://github.com/corelight/CVE-2020-16898
Affected Systems and Versions
- Product: Linksys E1700 Wireless Router
- Firmware: 1.0.0.4.003
- Only this firmware version is confirmed affected. Other Linksys products, including RE series range extenders, have similar but distinct vulnerabilities.
- The vulnerability is present whenever the web interface is accessible, and especially when the interface is exposed to untrusted networks.
Vendor Security History
- Multiple stack-based buffer overflows were reported in Linksys products in 2025, including CVE-2025-9392 and CVE-2025-9393.
- The vendor has a history of not responding to coordinated disclosure and of not releasing timely patches for critical issues.
- Linksys has published no official advisory or patch for CVE-2025-9527 as of the publication date.
