CVE-2026-86132 in Fireware OS
Summary
by MITRE • 09/30/2026
An integer underflow vulnerability in the WatchGuard Fireware OS IKEv2 daemon (iked) allows a remote, unauthenticated attacker to crash the process by sending a specially crafted encrypted IKEv2 message negotiated with an AES-GCM cipher suite.
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Analysis
by VulDB Data Team • 09/30/2026
The identified security flaw resides within the Internet Key Exchange version 2 implementation of the WatchGuard Fireware operating system, specifically affecting the iked daemon responsible for managing secure key exchanges in IPsec tunnels. This vulnerability is classified as an integer underflow, a type of logic error where a subtraction operation results in a negative value that exceeds the minimum limit of the variable's data type. In this specific context, the flaw occurs during the processing of encrypted IKEv2 messages when negotiated with AES-GCM cipher suites. The underlying technical mechanism involves improper validation or arithmetic handling of packet length fields or counter values associated with the authenticated encryption process. When a remote attacker sends a specially crafted message designed to trigger this miscalculation, the system fails to correctly account for the resulting negative integer, leading to an out-of-bounds memory access or invalid pointer dereference within the daemon's execution context.
From a technical perspective, this vulnerability aligns with CWE-192, which defines integer underflow as a condition where an arithmetic operation results in a value smaller than what can be represented by the target data type. The exploitation of this flaw does not require authentication, allowing any network actor to interact with the IKEv2 service on port 500 or UDP port 4500 depending on NAT traversal configurations. By sending malformed packets that exploit the underflow condition during the decryption and integrity verification phase of AES-GCM processing, an attacker can cause the iked process to encounter a fatal exception. This results in the immediate termination or crash of the IKEv2 daemon service rather than allowing for arbitrary code execution at this stage. The absence of authentication requirements significantly lowers the barrier for exploitation, making it accessible to automated scanning tools and opportunistic attackers targeting exposed firewall management interfaces or IPsec endpoints.
The operational impact of this vulnerability is primarily centered on availability and service disruption. Since the iked daemon handles critical key exchange operations necessary for establishing and maintaining secure tunnels, its crash effectively breaks ongoing IPsec connections and prevents new ones from being established until the service is restarted. For enterprise environments relying on WatchGuard firewalls as perimeter security devices or site-to-site VPN gateways, this can lead to significant network outages affecting remote users, branch office connectivity, and cloud infrastructure integrations that depend on persistent secure tunnels. While the immediate effect is a denial of service through process termination, repeated crashes may also impact system stability if watchdog mechanisms fail to restart the daemon promptly or if the crash triggers broader resource exhaustion conditions in constrained environments.
Mitigation strategies must focus on both technical remediation and architectural controls until official patches are applied by WatchGuard. The primary defense involves applying vendor-provided firmware updates that address the integer underflow logic within the iked component, ensuring proper bounds checking and validation of all input parameters derived from IKEv2 messages. In scenarios where immediate patching is not feasible, network segmentation should be employed to restrict access to UDP ports 500 and 4500 exclusively to trusted IP addresses or subnets known for legitimate VPN traffic. Additionally, deploying intrusion prevention systems with signatures capable of detecting malformed IKEv2 packets can provide a layer of defense against exploitation attempts. Organizations should also monitor system logs for unexpected restarts of the iked service as an indicator of potential active probing or successful exploitation events. Adhering to these controls helps maintain the integrity and availability of critical network infrastructure while addressing the underlying CWE-192 flaw through software updates and access restriction policies aligned with ATT&CK techniques related to resource hijacking and denial of service via application layer attacks.