CVE-2026-78011 in Fireware OS
Summary
by MITRE • 08/28/2026
An integer underflow vulnerability in the WatchGuard Fireware OS iked process allows a remote unauthenticated attacker to create a Denial of Service (DoS) condition in VPN processing by sending specially crafted network traffic.
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Analysis
by VulDB Data Team • 08/28/2026
The identified vulnerability resides within the Internet Key Exchange daemon, commonly referred to as iked, which is a critical component of the WatchGuard Fireware operating system responsible for managing IPsec security associations and key exchange protocols. This specific flaw manifests as an integer underflow condition during the processing of incoming network packets intended for VPN establishment or maintenance. The root cause lies in insufficient validation checks within the parsing logic that handles numeric fields associated with IKE payloads. When a remote, unauthenticated attacker transmits specially crafted traffic containing malformed numerical values, the system fails to properly account for negative results when subtracting smaller unsigned integers from larger ones or performing similar arithmetic operations without adequate boundary verification. This logical error allows the internal state of the iked process to enter an invalid configuration, leading directly to a denial of service condition where VPN processing capabilities are disrupted or the daemon crashes entirely.
From a technical perspective, this vulnerability aligns with CWE-192, which classifies integer underflow errors that occur when arithmetic operations produce results smaller than can be represented by the target data type. In the context of network daemons like iked, such flaws often lead to buffer overflows or logic bypasses if the resulting negative value is subsequently used as an array index or memory allocation size without proper casting checks. However, in this specific instance, the primary impact observed is a service disruption rather than code execution. The attacker does not need valid credentials or prior authentication because the vulnerability triggers during the initial handshake phases of IKE negotiation, which are designed to be accessible to any peer seeking to establish a secure tunnel. This lack of pre-authentication requirement significantly lowers the barrier for exploitation, allowing anyone with network access to target the vulnerable service endpoint.
The operational impact of this flaw is severe in environments relying heavily on IPsec connectivity for remote access or site-to-site VPNs. A successful exploit results in the degradation or complete failure of VPN services, effectively blocking legitimate users from establishing secure connections through the WatchGuard firewall. This denial of service can be achieved with minimal effort and resources, as it requires only the transmission of specific packet sequences rather than complex multi-stage attacks. For organizations dependent on continuous connectivity for business operations, remote workforces, or inter-office communication, this vulnerability represents a significant availability risk. The persistence of the issue implies that repeated attempts may cause intermittent outages or require manual intervention to restart services, thereby increasing administrative overhead and reducing overall system reliability during active exploitation campaigns.
Mitigation strategies must address both immediate remediation and long-term architectural resilience. The primary defense is the application of vendor-provided software updates that patch the integer underflow logic within the iked process. Administrators should verify their current firmware version against known good baselines and apply patches as soon as they become available from WatchGuard support channels. In scenarios where immediate patching is not feasible, network-level mitigations can be employed to reduce exposure. This includes restricting access to IKE ports (typically UDP 500 and 4500) using Access Control Lists or firewall rules that limit source IP addresses to trusted networks only. Additionally, enabling strict packet inspection features if available on the platform may help detect and drop malformed packets before they reach the vulnerable parsing logic. Organizations should also monitor logs for unusual spikes in IKE negotiation failures or service restarts, which could indicate ongoing exploitation attempts.
This vulnerability is categorized under MITRE ATT&CK technique T1498, Network Denial of Service, specifically reflecting direct network-based attacks that disrupt availability without compromising confidentiality or integrity. It also relates to CWE-20, Improper Input Validation, as the core failure stems from inadequate sanitization and validation of external data inputs before processing. Understanding these classifications helps security teams contextualize the risk within broader threat landscapes and prioritize remediation efforts based on industry-standard frameworks. By addressing this flaw promptly and implementing layered defenses, organizations can maintain the integrity and availability of their VPN infrastructure against both automated scanning tools and targeted denial-of-service attacks leveraging similar integer arithmetic weaknesses in network services.