CVE-2026-19314: WatchGuard Fireware OS VPN DoS Vulnerability

CVE-2026-19314 Overview

CVE-2026-19314 is an integer underflow vulnerability [CWE-191] in the WatchGuard Fireware OS iked process. The iked daemon handles Internet Key Exchange (IKE) negotiation for VPN connections on WatchGuard firewalls. A remote unauthenticated attacker can send specially crafted network traffic to trigger the underflow and disrupt VPN processing. Successful exploitation results in a Denial of Service (DoS) condition affecting VPN availability on the appliance.

Critical Impact
Unauthenticated network attackers can disable VPN services on affected WatchGuard Fireware OS appliances, disrupting remote access and site-to-site tunnels used by the organization.

Affected Products

WatchGuard Fireware OS (see the WatchGuard PSIRT advisory for the affected version matrix)
WatchGuard Firebox appliances running vulnerable Fireware OS builds
Deployments using the iked IKE/IPsec VPN service

Discovery Timeline

2026-08-28 - CVE-2026-19314 published to NVD
2026-09-03 - Last updated in NVD database

Technical Details for CVE-2026-19314

Vulnerability Analysis

The vulnerability resides in the iked process, which negotiates IKE/IPsec Security Associations for VPN tunnels. The daemon performs arithmetic on values derived from attacker-controlled IKE message fields. Under specific input conditions, a subtraction produces a value below zero and wraps to a large unsigned integer.

The wrapped value is then used as a length or offset when parsing subsequent payloads. This leads to invalid memory access or oversized processing loops inside iked. The process terminates or hangs, and VPN negotiation stops for all clients until the service recovers.

Because iked is reachable from any host that can send UDP traffic to the firewall's IKE ports (500/udp and 4500/udp for NAT-Traversal), no authentication or user interaction is required. The attack targets availability of VPN processing only; confidentiality and integrity of data are not affected according to the CVSS metrics.

Root Cause

The root cause is an integer underflow [CWE-191] in the IKE message parsing logic of iked. The code subtracts a header or field size from a length value taken directly from the network packet. When the supplied length is smaller than the fixed subtrahend, the unsigned result underflows. Missing bounds validation before the arithmetic operation allows the malformed value to reach downstream memory operations.

Attack Vector

Exploitation requires only network reachability to the IKE listener on the Firebox appliance. The attacker crafts an IKE packet with manipulated length fields that trigger the underflow during parsing. The packet is delivered to 500/udp or 4500/udp. Repeated packets can sustain the DoS condition and keep VPN services unavailable.

No verified public proof-of-concept code is available at this time. Refer to the WatchGuard CVE-2026-19314 Advisory for authoritative technical details.

Detection Methods for CVE-2026-19314

Indicators of Compromise

Unexpected termination or repeated restarts of the iked process in Fireware OS logs
Sudden loss of active IKE Security Associations and failed VPN client reconnections
Unusual bursts of malformed IKE packets to 500/udp or 4500/udp from a single or small set of source addresses
Firebox diagnostic logs containing IKE parsing errors or abnormal payload length warnings

Detection Strategies

Monitor Fireware OS system logs for iked crashes, restarts, and IKE payload parsing errors
Alert on rapid drops in the count of established IPsec/IKE tunnels on the appliance
Inspect IKE traffic at network sensors for oversized or truncated payload length fields that violate RFC 7296 constraints

Monitoring Recommendations

Forward Firebox syslog to a centralized logging platform and build dashboards for iked process health
Track VPN session availability metrics and page on-call when tunnel counts drop below baseline
Baseline normal IKE traffic sources and alert on new external IPs generating high volumes of IKE requests

How to Mitigate CVE-2026-19314

Immediate Actions Required

Apply the fixed Fireware OS version documented in the WatchGuard PSIRT advisory as soon as it is available for your appliance model
Restrict IKE exposure by limiting 500/udp and 4500/udp access to known VPN peer IP addresses where operationally feasible
Enable automated recovery so that iked restarts promptly if terminated, reducing outage duration

Patch Information

WatchGuard has published advisory information for CVE-2026-19314 at psirt.watchguard.com/CVE-2026-19314. Review the advisory for the list of affected Fireware OS versions and the corresponding fixed builds for each Firebox model. Upgrade appliances through WatchGuard System Manager or the Fireware Web UI following the vendor's standard update procedure.

Workarounds

Apply firewall policies that permit IKE traffic only from authorized branch-office and remote-access peer IPs
Front the VPN listener with an upstream device or ACL that drops malformed IKE packets before they reach iked
If mobile VPN is not in use, temporarily disable the IKE service until the patched Fireware OS build is deployed

bash

# Example: restrict IKE ports to known peer IPs on an upstream ACL
# Replace peer addresses with your authorized VPN endpoints
access-list VPN_PEERS permit udp host 203.0.113.10 any eq 500
access-list VPN_PEERS permit udp host 203.0.113.10 any eq 4500
access-list VPN_PEERS deny   udp any any eq 500
access-list VPN_PEERS deny   udp any any eq 4500