CVE-2025-9242: WatchGuard Fireware OS RCE Vulnerability

CVE-2025-9242 Overview

CVE-2025-9242 is a critical Out-of-bounds Write vulnerability affecting WatchGuard Fireware OS that enables remote unauthenticated attackers to execute arbitrary code on vulnerable firewall appliances. This vulnerability specifically impacts the IKEv2 protocol implementation used by both Mobile User VPN and Branch Office VPN configurations when a dynamic gateway peer is configured.

The vulnerability is particularly severe as it requires no authentication and can be exploited remotely over the network, making it an attractive target for threat actors seeking to compromise enterprise perimeter security devices. WatchGuard firewalls serve as the primary defense layer for many organizations, making successful exploitation of this vulnerability especially impactful.

Critical Impact

This vulnerability has been added to CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild. Remote unauthenticated attackers can achieve arbitrary code execution on affected WatchGuard firewall appliances, potentially compromising entire network perimeters.

Affected Products

• WatchGuard Fireware OS versions 11.10.2 through 11.12.4_Update1
• WatchGuard Fireware OS versions 12.0 through 12.11.3
• WatchGuard Fireware OS version 2025.1
• WatchGuard Firebox M-Series (M270, M290, M370, M390, M440, M470, M570, M590, M670, M690, M4600, M4800, M5600, M5800)
• WatchGuard Firebox T-Series (T15, T20, T25, T35, T40, T45, T55, T70, T80, T85, T115-W, T125, T125-W, T145, T145-W, T185)
• WatchGuard Firebox NV5
• WatchGuard FireboxCloud and FireboxV virtual appliances

Discovery Timeline

• September 17, 2025 - CVE-2025-9242 published to NVD
• November 14, 2025 - Last updated in NVD database

Technical Details for CVE-2025-9242

Vulnerability Analysis

This Out-of-bounds Write vulnerability (CWE-787) resides in the IKEv2 protocol handler within WatchGuard Fireware OS. When processing IKEv2 negotiation packets for VPN connections, the affected code fails to properly validate the boundaries of data being written to memory buffers. An attacker can craft malicious IKEv2 packets that cause data to be written beyond allocated buffer boundaries, corrupting adjacent memory regions.

The vulnerability is accessible remotely without authentication because IKEv2 must process initial connection packets before any authentication occurs. This pre-authentication attack surface makes the vulnerability particularly dangerous, as attackers only need network access to the VPN service ports to attempt exploitation.

Both Mobile User VPN (for remote client connections) and Branch Office VPN (for site-to-site tunnels) implementations share the vulnerable IKEv2 code path. The vulnerability is triggered when dynamic gateway peers are configured, a common deployment pattern for organizations with remote users or branch offices with dynamic IP addresses.

Root Cause

The root cause is improper bounds checking in the IKEv2 packet processing code. When handling specially crafted IKEv2 payloads, the Fireware OS fails to validate that write operations remain within the bounds of allocated memory buffers. This allows an attacker-controlled payload to overflow the intended buffer and overwrite adjacent memory, potentially including function pointers, return addresses, or other security-critical data structures.

Attack Vector

The attack vector is network-based, targeting the IKEv2 service (typically UDP port 500 and 4500) exposed on WatchGuard firewall appliances configured for VPN services. An attacker can exploit this vulnerability by:

1. Identifying a WatchGuard firewall with exposed IKEv2 VPN services
2. Sending specially crafted IKEv2 negotiation packets to the target
3. Triggering the out-of-bounds write condition during packet processing
4. Achieving code execution in the context of the firewall's VPN service

The vulnerability does not require valid credentials or an existing VPN session, significantly lowering the barrier to exploitation. A proof-of-concept exploit has been published by watchTowr Labs, which is available on their GitHub repository.

Detection Methods for CVE-2025-9242

Indicators of Compromise

• Anomalous IKEv2 traffic patterns with malformed or unusually large payloads targeting UDP ports 500 and 4500
• Unexpected firewall service restarts or crashes, particularly involving VPN-related processes
• Evidence of unauthorized configuration changes or new administrative accounts on WatchGuard appliances
• Network traffic anomalies originating from the firewall appliance to unexpected external destinations

Detection Strategies

• Deploy network intrusion detection rules to identify malformed IKEv2 packets with oversized or malicious payloads
• Monitor WatchGuard syslog output for unusual VPN service errors, crashes, or memory-related exceptions
• Implement behavioral analysis to detect post-exploitation activity such as reverse shells or data exfiltration from firewall management interfaces
• Correlate firewall logs with threat intelligence feeds that include indicators associated with CVE-2025-9242 exploitation

Monitoring Recommendations

• Enable verbose logging for IKEv2 VPN services on all WatchGuard appliances and centralize logs for analysis
• Configure alerting for firewall service instability or unexpected reboots that could indicate exploitation attempts
• Monitor for any unauthorized changes to firewall policies, user accounts, or VPN configurations
• Establish baseline metrics for VPN connection patterns to identify anomalous connection attempts

How to Mitigate CVE-2025-9242

Immediate Actions Required

• Immediately apply the security patches released by WatchGuard as documented in Security Advisory WGSA-2025-00015
• If patching is not immediately possible, consider temporarily disabling IKEv2 VPN services and switching to alternative VPN protocols
• Restrict network access to IKEv2 ports (UDP 500 and 4500) to only trusted source IP ranges where feasible
• Review firewall configurations for any signs of compromise and validate the integrity of existing configurations

Patch Information

WatchGuard has released security updates to address CVE-2025-9242. Organizations should upgrade to patched versions of Fireware OS as specified in the WatchGuard Security Advisory. Given that this vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, federal agencies and organizations following CISA guidance should prioritize remediation according to binding operational directives.

Affected version ranges include:

• Fireware OS 11.10.2 through 11.12.4_Update1
• Fireware OS 12.0 through 12.11.3
• Fireware OS 2025.1

Workarounds

• Disable IKEv2 VPN functionality if not operationally required and utilize alternative VPN protocols such as IPSec with IKEv1 or SSL VPN
• Implement network-level access controls to limit exposure of VPN services to trusted IP addresses only
• Deploy additional network security controls such as IPS/IDS systems to filter malicious IKEv2 traffic before it reaches the firewall
• Consider implementing a VPN gateway in front of the WatchGuard appliance as a temporary protective measure