CVE-2026-19509: RDK-B WebUI DoS Vulnerability

CVE-2026-19509 Overview

CVE-2026-19509 is an improper input validation vulnerability in the RDK-B (Reference Design Kit for Broadband) WebUI. The flaw resides in the ajaxSet_wireless_network_configuration.jst handler within rdkb-2025q4-kirkstone.04.10.26. An authenticated attacker can trigger a denial of service by supplying a crafted ssid_number parameter. The vulnerability affects broadband gateway devices that use the RDK-B WebUI component to manage wireless network settings.

Critical Impact
Authenticated attackers can disrupt WebUI availability on affected RDK-B broadband devices by sending a malformed ssid_number value, interrupting wireless management operations.

Affected Products

RDK-B WebUI component in rdkb-2025q4-kirkstone.04.10.26
Broadband gateways and routers built on the RDK-B reference stack
Deployments exposing ajaxSet_wireless_network_configuration.jst to authenticated users

Discovery Timeline

2026-08-19 - CVE-2026-19509 published to NVD
2026-08-19 - Last updated in NVD database

Technical Details for CVE-2026-19509

Vulnerability Analysis

The vulnerability exists in ajaxSet_wireless_network_configuration.jst, a server-side template used by the RDK-B WebUI to apply wireless configuration changes. The handler accepts an ssid_number parameter that identifies the target SSID index. The code fails to validate this parameter before using it in subsequent operations. An authenticated attacker submits a crafted ssid_number value that the handler cannot process safely, triggering a denial of service condition on the WebUI or the underlying management daemon.

This is an input validation weakness in the request-processing layer of the WebUI. Because the WebUI mediates wireless configuration, disruption of the handler impacts operator ability to view or modify wireless settings.

Root Cause

The root cause is missing or insufficient validation of the ssid_number request parameter inside ajaxSet_wireless_network_configuration.jst. The handler assumes the parameter is a well-formed index. When an attacker supplies an unexpected type, out-of-range value, or malformed content, the handler enters an error state that terminates or hangs the process. See the WhiteHat Blog on RDKB Vulnerabilities for the researcher writeup.

Attack Vector

Exploitation requires authenticated access to the RDK-B WebUI. An attacker submits an HTTP request to the ajaxSet_wireless_network_configuration.jst endpoint with a crafted ssid_number field. The malformed value causes the handler to fail, disrupting WebUI availability and wireless configuration workflows. See RDK Central Documentation for component context.

Detection Methods for CVE-2026-19509

Indicators of Compromise

HTTP POST or GET requests to ajaxSet_wireless_network_configuration.jst containing non-numeric, oversized, or out-of-range ssid_number values
Unexpected WebUI process crashes or restarts on RDK-B gateways following authenticated management sessions
Repeated authentication-followed-by-crash patterns in WebUI access logs

Detection Strategies

Inspect WebUI request logs for anomalous ssid_number parameter values that deviate from the expected small integer range
Correlate authenticated WebUI sessions with subsequent management-plane availability loss
Alert on RDK-B WebUI process termination events tied to specific source addresses

Monitoring Recommendations

Forward RDK-B WebUI and system logs to a centralized log platform for pattern analysis
Track failed and abnormal ajaxSet_*.jst requests per authenticated account
Monitor management interface availability with synthetic checks against the WebUI

How to Mitigate CVE-2026-19509

Immediate Actions Required

Restrict WebUI access to trusted management networks and VLANs
Enforce strong, unique credentials on all RDK-B WebUI accounts and rotate defaults
Reduce the number of accounts with WebUI login rights to the minimum required
Rate-limit requests to ajaxSet_wireless_network_configuration.jst at the network edge

Patch Information

No vendor patch reference is listed in the NVD entry at publication. Operators should track upstream RDK-B releases beyond rdkb-2025q4-kirkstone.04.10.26 and apply fixes issued by device manufacturers that integrate the RDK-B WebUI. Consult the RDK Central Documentation and vendor advisories for update availability.

Workarounds

Block external access to the WebUI and expose it only over an internal management network
Add a reverse proxy or WAF rule that rejects ssid_number values outside the expected numeric range
Disable remote WebUI access on customer-premises equipment where operator management is handled out-of-band
Monitor for and automatically restart the WebUI service if it terminates unexpectedly

bash

# Example reverse-proxy rule concept: reject non-numeric or oversized ssid_number values
# Pseudocode - adapt to your proxy or WAF syntax
if ($arg_ssid_number !~ '^[0-9]{1,2}$') {
    return 400;
}