CVE-2026-17518: ASUS Router Buffer Overflow DoS Vulnerability

CVE-2026-17518 Overview

CVE-2026-17518 is a stack-based buffer overflow vulnerability affecting certain ASUS router models. The flaw stems from a buffer copy operation that does not validate the size of input data, classified under [CWE-121]. An adjacent authenticated attacker can send a crafted HTTP request containing input that exceeds the expected length, corrupting device operations and causing a denial of service condition on the targeted router.

Critical Impact

An adjacent authenticated attacker can disrupt router operations and cause a denial of service by submitting an oversized HTTP request to the vulnerable web management interface.

Affected Products

• ASUS Router Firmware (specific models listed in the ASUS Security Advisory)
• Devices exposing the affected HTTP management interface on adjacent networks
• Refer to the ASUS Security Advisory for the complete list of affected models and firmware versions

Discovery Timeline

• 2026-10-20 - CVE-2026-17518 published to the National Vulnerability Database
• 2026-10-20 - Last updated in NVD database

Technical Details for CVE-2026-17518

Vulnerability Analysis

The vulnerability resides in HTTP request handling code within affected ASUS router firmware. The firmware performs a buffer copy operation without first validating the length of attacker-supplied input against the destination buffer size. When an authenticated user on an adjacent network sends an HTTP request containing a field that exceeds the expected length, the copy operation writes past the bounds of a stack-allocated buffer.

This stack corruption can overwrite adjacent stack memory, including saved return addresses and local variables used by the handling function. The immediate observed effect is corruption of device operations and a denial of service as the firmware process crashes or enters an inconsistent state. The attack requires network adjacency and valid authentication credentials, limiting remote exploitation but remaining relevant for shared or compromised network segments.

Root Cause

The root cause is a missing bounds check prior to a buffer copy operation, consistent with [CWE-121] Stack-Based Buffer Overflow. The affected routine trusts the length of HTTP request input and copies it directly into a fixed-size stack buffer, allowing overflow when input exceeds the buffer's capacity.

Attack Vector

Exploitation requires an attacker positioned on an adjacent network with valid authentication to the router's web management interface. The attacker crafts an HTTP request where one or more input fields exceed the expected length. Upon processing, the router firmware corrupts stack memory and ceases normal operation, resulting in denial of service. Full technical details of the vulnerable parameter are not disclosed in the public advisory. See the ASUS Security Advisory for additional context.

Detection Methods for CVE-2026-17518

Indicators of Compromise

• Unexpected router reboots, crashes, or loss of management plane availability following HTTP requests to the admin interface
• HTTP requests to the router administration interface containing unusually long parameter values or header fields
• Repeated authentication followed by malformed or oversized HTTP POST requests from adjacent network hosts

Detection Strategies

• Inspect HTTP traffic destined for router management interfaces for request fields that exceed documented length limits
• Correlate router availability events with preceding authenticated administrative sessions from internal hosts
• Monitor router system logs for process crashes, watchdog resets, or management daemon restarts

Monitoring Recommendations

• Enable syslog forwarding from affected routers to a central logging platform for crash and reboot event visibility
• Alert on anomalous administrative authentication events from unusual adjacent network sources
• Track network segment reachability metrics to detect short-duration router outages indicative of exploitation attempts

How to Mitigate CVE-2026-17518

Immediate Actions Required

• Apply the firmware update published in the ASUS Security Advisory to all affected router models
• Restrict access to the router web management interface to trusted administrative hosts only
• Rotate administrative credentials and disable unused accounts on affected devices
• Audit the list of adjacent network users who hold authenticated access to the router

Patch Information

ASUS has released firmware updates addressing CVE-2026-17518. Consult the ASUS Security Advisory, specifically the "Security Update for ASUS Router Firmware" section, to identify the fixed firmware version for your model and apply the update through the router administrative interface or the ASUS firmware download portal.

Workarounds

• Disable remote administration features and limit management access to a dedicated management VLAN
• Enforce strong, unique administrative passwords and enable account lockout protections where supported
• Place the router management interface behind access control lists that permit only authorized administrator IP addresses
• Segment untrusted wireless or guest networks away from the router management interface

# Example: restrict router management access to a specific admin host
# (adjust per your network and router capabilities)
allow_mgmt_source="192.0.2.10/32"
mgmt_interface="br-lan"

iptables -I INPUT -i $mgmt_interface -p tcp --dport 80  -s $allow_mgmt_source -j ACCEPT
iptables -I INPUT -i $mgmt_interface -p tcp --dport 443 -s $allow_mgmt_source -j ACCEPT
iptables -A INPUT -i $mgmt_interface -p tcp --dport 80  -j DROP
iptables -A INPUT -i $mgmt_interface -p tcp --dport 443 -j DROP