CVE-2026-78010: WatchGuard Fireware OS DoS Vulnerability

CVE-2026-78010 Overview

CVE-2026-78010 is a stack-based buffer overflow in the WatchGuard Fireware OS iked process. The iked daemon handles Internet Key Exchange (IKE) negotiation for IPsec VPN connections. A remote unauthenticated attacker can send specially crafted network traffic to trigger the overflow and disrupt VPN processing. Successful exploitation produces a Denial of Service (DoS) condition affecting VPN availability on the firewall. The flaw maps to CWE-121 (Stack-based Buffer Overflow) and requires no authentication or user interaction.

Critical Impact
Unauthenticated remote attackers can crash the IKE daemon and disable IPsec VPN services on affected WatchGuard Fireware OS appliances.

Affected Products

WatchGuard Fireware OS (see vendor advisory for affected version ranges)
WatchGuard Firebox appliances running vulnerable Fireware OS builds
Any deployment exposing the iked process on network-reachable interfaces

Discovery Timeline

2026-08-28 - CVE-2026-78010 published to NVD
2026-09-03 - Last updated in NVD database

Technical Details for CVE-2026-78010

Vulnerability Analysis

The vulnerability resides in the iked process, which negotiates IKE/IPsec security associations on WatchGuard Fireware OS. The daemon fails to validate the length of attacker-controlled fields in IKE messages before copying them onto a fixed-size stack buffer. Sending a malformed IKE packet overflows the buffer and corrupts adjacent stack memory, causing the process to crash. When iked terminates, active VPN tunnels drop and new tunnel negotiations fail until the service restarts. This directly impacts availability of site-to-site and remote-access VPN services on the firewall.

Root Cause

The root cause is missing or insufficient bounds checking on IKE protocol fields parsed from untrusted network input, classified under CWE-121. Fixed-size stack buffers receive variable-length data from attacker-controlled packets without prior length validation. This overwrite corrupts stack frames including saved return addresses and canaries, causing the daemon to terminate. Refer to the WatchGuard CVE-2026-78010 Advisory for vendor-confirmed technical details.

Attack Vector

Exploitation is remote and network-based. Attackers send crafted IKE UDP traffic (typically to ports 500/UDP and 4500/UDP) toward any interface where iked accepts negotiation. No credentials or user interaction are required. The vendor advisory scopes the impact to a DoS condition against VPN processing rather than code execution. See the WatchGuard CVE-2026-78010 Advisory for confirmed vectors and prerequisites.

No verified proof-of-concept code is publicly available. The vulnerability manifests in the IKE message parsing path within iked; see the vendor advisory for technical details.

Detection Methods for CVE-2026-78010

Indicators of Compromise

Unexpected termination or restart of the iked process in Fireware OS logs
Sudden drop of active IPsec Security Associations across multiple peers
Repeated malformed IKE_SA_INIT or IKE_AUTH packets to UDP/500 or UDP/4500
VPN client reconnection storms following short-duration outages

Detection Strategies

Monitor Fireware system logs for iked crashes, core dumps, or watchdog-triggered restarts
Inspect IKE traffic at network sensors for oversized or malformed payload attributes
Alert on abnormal spikes in inbound UDP/500 and UDP/4500 traffic from single sources
Correlate VPN tunnel down events with concurrent IKE traffic anomalies

Monitoring Recommendations

Forward Fireware OS syslog to a centralized SIEM and alert on iked process events
Track IPsec tunnel uptime metrics via SNMP or vendor telemetry to detect service disruption
Baseline normal IKE peer counts and alert on statistically significant deviations
Retain packet captures on management interfaces for post-incident IKE payload analysis

How to Mitigate CVE-2026-78010

Immediate Actions Required

Apply the fixed Fireware OS release identified in the WatchGuard CVE-2026-78010 Advisory as soon as available
Restrict IKE (UDP/500) and NAT-T (UDP/4500) exposure to known VPN peer IP addresses where feasible
Enable configuration and log backups prior to patching to support rapid recovery
Notify VPN users of possible short outages during the patch window

Patch Information

WatchGuard publishes patched Fireware OS builds through its PSIRT portal. Consult the WatchGuard CVE-2026-78010 Advisory for the exact fixed version and upgrade path for each Firebox model. Verify build integrity after upgrade and confirm the iked process is running the patched binary.

Workarounds

Apply geographic or IP-based access policies to limit which sources can reach UDP/500 and UDP/4500
Place upstream rate limiting or IPS signatures to drop malformed IKE payloads
Where VPN is not required, disable Mobile VPN with IKEv2 and branch office IPsec temporarily
Monitor iked health and configure automatic service restart to reduce outage duration

bash

# Example: restrict IKE/NAT-T to known peer subnets on an upstream device
# Replace 203.0.113.0/24 with your authorized VPN peer range
iptables -A FORWARD -p udp --dport 500  -s 203.0.113.0/24 -j ACCEPT
iptables -A FORWARD -p udp --dport 4500 -s 203.0.113.0/24 -j ACCEPT
iptables -A FORWARD -p udp --dport 500  -j DROP
iptables -A FORWARD -p udp --dport 4500 -j DROP