CVE-2026-113881 in Fireware OS
Summary
by MITRE • 10/27/2026
A stack-based buffer overflow vulnerability in Fireware OS's VPN Network Access Enforcement process allows an authenticated mobile VPN user to create a denial of service condition and potentially execute arbitrary code as an unprivileged process by sending a specially crafted request.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability resides within the Firewalla Operating System, specifically affecting the Virtual Private Network Network Access Enforcement subsystem. This component is responsible for validating and enforcing access policies for mobile VPN users attempting to establish or maintain connections through the firewall appliance. The core technical flaw is a stack-based buffer overflow, which occurs when the system fails to properly validate the length of input data received from an authenticated user before copying it into a fixed-size memory buffer on the call stack. This lack of bounds checking allows an attacker who has already successfully authenticated as a mobile VPN user to supply a specially crafted request containing oversized or malformed data that exceeds the allocated buffer capacity.
When this malicious payload is processed, the excess data overwrites adjacent memory locations on the stack, potentially corrupting critical control structures such as return addresses and saved frame pointers. This corruption can lead to two distinct operational outcomes depending on the specific execution context and memory layout. In many scenarios, the immediate result is a denial of service condition where the VPN enforcement process crashes or becomes unresponsive, effectively disrupting connectivity for all users relying on that particular firewall instance. However, if an attacker successfully manipulates the overwritten return address to point to injected shellcode or existing executable code within the process memory space, they can achieve arbitrary code execution.
It is crucial to note that this exploitation requires prior authentication as a mobile VPN user. This prerequisite limits the attack surface significantly compared to unauthenticated remote exploits but still poses a severe risk because it allows privilege escalation from an authenticated low-privilege state to potentially higher levels of control within the system context, albeit described here as executing code as an unprivileged process initially. The ability to execute arbitrary code in this manner undermines the fundamental security assumptions of network segmentation and access control provided by the firewall. An attacker could leverage this foothold to pivot laterally across the protected network, exfiltrate sensitive data, or install persistent malware that evades standard perimeter defenses.
From a classification perspective, this vulnerability aligns with CWE-120 Buffer Copy without Checking Size of Input Classic and CWE-787 Out-of-bounds Write in terms of its root cause mechanism. In the context of offensive security tactics, it maps to ATT&CK technique T1059 Command and Scripting Interpreter if used for initial execution or T1068 Exploitation for Privilege Escalation depending on the final outcome. The vulnerability highlights a critical gap in input validation practices within network infrastructure software, particularly regarding how user-supplied data is handled during policy enforcement operations.
Mitigation strategies must focus on immediate patching of the Firewalla OS to the latest version that addresses this specific buffer overflow issue. Administrators should verify their current firmware versions and apply vendor-provided updates as soon as they become available. In environments where immediate patching is not feasible, network segmentation policies can be tightened to restrict VPN access only to trusted IP ranges or require multi-factor authentication alongside standard credentials to reduce the likelihood of an attacker obtaining valid mobile VPN credentials. Additionally, deploying intrusion prevention systems that detect anomalous packet sizes or malformed requests directed at VPN endpoints may provide a layer of defense in depth against exploitation attempts while patches are being deployed. Regular auditing of access logs for unusual patterns related to VPN connection establishment can also aid in early detection of potential exploitation activities.