CVE-2025-27851: Garmin WDU WebSocket Hijacking Vulnerability

CVE-2025-27851 Overview

CVE-2025-27851 is a cross-site WebSocket hijacking vulnerability affecting the locally served web site on the Garmin Wireless Display Unit (WDU). The flaw impacts WDU v1 firmware 1.4.6 and WDU v2 firmware 5.0. The WDU uses WebSockets to control device settings, including administrative settings, without enforcing cross-origin protections. An attacker on the Garmin Marine Network can take full control of a WDU when a victim browses a malicious third-party site from a multihomed host.

Critical Impact

Successful exploitation grants the attacker administrative control over the Garmin WDU, including the ability to modify settings on the Marine Network.

Affected Products

• Garmin WDU v1 firmware 1.4.6
• Garmin WDU v2 firmware 5.0
• Devices on the Garmin Marine Network reachable from multihomed browser hosts

Discovery Timeline

• 2026-05-13 - CVE-2025-27851 published to the National Vulnerability Database (NVD)
• 2026-05-13 - Last updated in NVD database

Technical Details for CVE-2025-27851

Vulnerability Analysis

The Garmin WDU exposes a locally served web interface that drives device configuration through WebSocket connections. The WebSocket endpoints do not validate the Origin header or require an unguessable per-session token. Any web page loaded in the victim's browser can therefore open a WebSocket to the WDU and issue privileged commands. Because the WDU treats network-local clients as trusted, the attacker inherits administrative access once the connection is established. This pattern is classified as Cross-Site WebSocket Hijacking, a subclass of Cross-Site Request Forgery (CSRF) for full-duplex transports.

Root Cause

The root cause is missing origin validation and absent CSRF protection on the WDU's WebSocket control channel. The server upgrades any HTTP request that meets the WebSocket handshake requirements regardless of the originating site. Administrative commands carried over the channel rely solely on network reachability for authorization.

Attack Vector

Exploitation requires two preconditions. First, the victim must browse from a multihomed host that has one interface attached to the Garmin Marine Network and another interface attached to a separate network such as the internet. Second, the victim must visit a malicious third-party page controlled by the attacker. JavaScript on that page opens a WebSocket to the WDU's local address, then issues setting and administrative commands through the hijacked channel. No credentials or user interaction beyond visiting the page are required.

The vulnerability is described in prose only; no verified proof-of-concept code is published. See the Garmin Support Page for vendor information.

Detection Methods for CVE-2025-27851

Indicators of Compromise

• Unexpected WebSocket upgrade requests to the WDU originating from browser user agents rather than Garmin client applications
• WDU configuration changes that do not correlate with operator activity at the helm
• Outbound HTTP requests from Marine Network hosts to unfamiliar third-party domains shortly before WDU setting changes

Detection Strategies

• Inspect WebSocket handshakes on the Marine Network for Origin headers that do not match the WDU's own host
• Baseline normal administrative command traffic to the WDU and alert on deviations in frequency or source
• Monitor browser-based hosts that bridge the Marine Network to other networks for cross-network traffic patterns

Monitoring Recommendations

• Capture and retain WebSocket frame metadata at network choke points between the Marine Network and other segments
• Log administrative setting changes on the WDU with timestamps and client IP addresses for forensic review
• Alert when a host simultaneously holds a route to the Marine Network and an active internet session

How to Mitigate CVE-2025-27851

Immediate Actions Required

• Stop using multihomed hosts that bridge the Garmin Marine Network with any other network, including the internet
• Restrict web browsing on any device that has an interface on the Marine Network
• Isolate the Garmin Marine Network from general-purpose LANs and Wi-Fi

Patch Information

No patch information is currently listed in the NVD entry for CVE-2025-27851. Consult the Garmin Official Website and the Garmin Support Page for firmware updates for WDU v1 and WDU v2.

Workarounds

• Use dedicated, single-homed devices for any interaction with the Garmin Marine Network
• Disable Wi-Fi or secondary network interfaces on chartplotters and tablets while connected to the Marine Network
• Avoid browsing untrusted websites from any host that can route to the WDU

# Configuration example: disable secondary interface while on Marine Network (Linux)
sudo ip link set dev wlan0 down
sudo ip route del default via <internet-gateway>