CVE-2025-9246: Linksys Re6250 Buffer Overflow Vulnerability

CVE-2025-9246 Overview

CVE-2025-9246 is a stack-based buffer overflow vulnerability affecting multiple Linksys range extender models. The flaw resides in the check_port_conflict function exposed via the /goform/check_port_conflict HTTP endpoint. Attackers can trigger the overflow by manipulating the single_port_rule or port_range_rule arguments. The vulnerability is classified under [CWE-119] for improper restriction of operations within the bounds of a memory buffer. The exploit has been publicly disclosed, and Linksys did not respond to early disclosure attempts. Affected devices include the RE6250, RE6300, RE6350, RE6500, RE7000, and RE9000 range extenders running specific firmware revisions.

Critical Impact

Remote attackers with low-privilege authentication can corrupt stack memory and potentially execute arbitrary code on affected Linksys range extenders.

Affected Products

• Linksys RE6250 firmware 1.0.04.001 and RE6350 firmware 1.0.04.001
• Linksys RE6300 firmware 1.2.07.001 and RE6500 firmware 1.0.013.001
• Linksys RE7000 firmware 1.1.05.003 and RE9000 firmware 1.0.04.002

Discovery Timeline

• 2025-08-20 - CVE-2025-9246 published to NVD
• 2025-09-02 - Last updated in NVD database

Technical Details for CVE-2025-9246

Vulnerability Analysis

The vulnerability exists in the check_port_conflict function reachable through the /goform/check_port_conflict web interface endpoint. The function processes user-supplied values from the single_port_rule and port_range_rule request parameters without enforcing length validation. Supplying oversized values overflows a fixed-size stack buffer, corrupting the saved return address and adjacent stack data.

Linksys range extenders run on resource-constrained embedded Linux systems, typically without modern exploit mitigations such as full Address Space Layout Randomization (ASLR) or stack canaries. This significantly increases the likelihood that a buffer overflow can be turned into reliable code execution. A successful exploit yields control over the embedded HTTP service, which usually runs with root privileges on the device.

Root Cause

The root cause is missing bounds checking on the single_port_rule and port_range_rule parameters before they are copied into a fixed-size local stack buffer inside check_port_conflict. The function uses an unsafe string copy operation that does not constrain the input length to the destination buffer size, mapping to [CWE-119].

Attack Vector

An attacker on the same network as the device, or one able to reach the web management interface remotely, can send a crafted HTTP request to /goform/check_port_conflict with overlong values in the vulnerable parameters. The CVSS vector indicates network reach with low attack complexity but requires low-level privileges, meaning the attacker must have access to the management interface or valid session credentials.

The vulnerability mechanism follows the classic stack-based buffer overflow pattern: oversized POST data targeting the vulnerable parameters overwrites the return address on the stack. Public proof-of-concept information is referenced in the GitHub Vulnerability Report and the VulDB entry #320777.

Detection Methods for CVE-2025-9246

Indicators of Compromise

• HTTP POST requests to /goform/check_port_conflict containing abnormally long single_port_rule or port_range_rule parameter values.
• Unexpected reboots or service crashes of the embedded HTTP daemon on affected range extenders.
• Outbound connections from range extender management IPs to unfamiliar external hosts following suspicious management traffic.

Detection Strategies

• Inspect web server and router logs for requests targeting /goform/check_port_conflict and flag parameter values exceeding reasonable port-rule lengths.
• Deploy network intrusion detection signatures that match oversized payloads in HTTP POST bodies destined for Linksys range extender management interfaces.
• Monitor for repeated 5xx responses or session resets originating from affected devices, which can indicate exploitation attempts.

Monitoring Recommendations

• Restrict management interface access to a dedicated administrative VLAN and log all access attempts.
• Forward device syslog and HTTP access logs to a centralized logging or SIEM platform for correlation against the indicators listed above.
• Track firmware versions across the fleet to identify devices still running vulnerable builds such as 1.0.013.001, 1.0.04.001, 1.0.04.002, 1.1.05.003, and 1.2.07.001.

How to Mitigate CVE-2025-9246

Immediate Actions Required

• Disable remote management on all affected RE6250, RE6300, RE6350, RE6500, RE7000, and RE9000 devices.
• Restrict access to the /goform/check_port_conflict endpoint via network segmentation and firewall ACLs.
• Rotate administrative credentials and audit existing sessions on affected devices.
• Plan replacement of end-of-support Linksys range extenders with currently supported hardware where no patch is available.

Patch Information

No vendor patch is currently available. According to the disclosure, Linksys was contacted but did not respond. Refer to the Linksys Official Website for any future advisories and the VulDB entry for tracking updates.

Workarounds

• Block external access to the device web management interface at the perimeter firewall.
• Place range extenders on an isolated management VLAN with no inbound access from untrusted networks.
• Disable the web administration interface when not actively configuring the device, where firmware supports doing so.
• Replace affected devices with supported models if vendor remediation does not become available.

# Example: restrict access to the range extender management interface
# Replace 192.0.2.10 with the device IP and 10.0.0.0/24 with the admin subnet
iptables -A FORWARD -p tcp -d 192.0.2.10 --dport 80 -s 10.0.0.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d 192.0.2.10 --dport 80 -j DROP
iptables -A FORWARD -p tcp -d 192.0.2.10 --dport 443 -s 10.0.0.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d 192.0.2.10 --dport 443 -j DROP