CVE-2026-77556 in Cloud Gateways
Summary
by MITRE • 09/22/2026
A malicious actor with access to the network could exploit an Out-of-bounds Read vulnerability found in certain UniFi gateway devices to execute a Denial of Service (DoS) attack on the device.
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Analysis
by VulDB Data Team • 09/22/2026
The identified security flaw represents a critical integrity violation within the firmware logic of specific UniFi gateway appliances, classified technically as an out-of-bounds read vulnerability. This type of memory safety error occurs when software attempts to access data at a memory address that lies outside the boundaries of the intended buffer or array structure. In the context of network infrastructure devices like gateways, such vulnerabilities are particularly dangerous because they reside in components responsible for high-volume packet processing and routing table management. The root cause typically stems from insufficient validation of input parameters during the parsing of network packets or configuration data structures. When a malicious actor with access to the local network segment sends specially crafted traffic designed to trigger this specific code path, the application fails to verify that the requested memory offset is valid before attempting to read it. This lack of boundary checking allows the system to retrieve arbitrary data from adjacent memory locations, which can lead to unpredictable behavior depending on what content resides in those neighboring memory spaces at the time of execution.
The operational impact of this vulnerability centers primarily on service availability rather than confidentiality or integrity in its immediate manifestation. While out-of-bounds reads are often associated with information disclosure where sensitive kernel data might be leaked back to the attacker, the specific exploitation scenario described highlights a denial of service outcome. This suggests that the malformed memory access triggers an exception handler within the operating system or application runtime environment, causing the process managing the network interface or routing engine to crash and terminate unexpectedly. For a gateway device, which serves as the primary choke point for all inbound and outbound traffic between internal networks and external internet connections, such a crash results in immediate connectivity loss. Users experience an interruption of service where no data can traverse the device until it is manually rebooted or automatically restarted by watchdog timers if configured to do so. This creates a persistent availability gap that disrupts business operations, remote access capabilities, and dependent cloud services hosted on or behind the affected infrastructure.
From a threat modeling perspective, this vulnerability aligns with Common Weakness Enumeration identifier CWE-125, which defines out-of-bounds read errors as software reading data past the end of an array or buffer. The exploitation vector is categorized under network-based attacks requiring local access to the compromised segment, placing it within the Initial Access and Execution phases of the MITRE ATT&CK framework for enterprise environments. Specifically, it relates to techniques involving crafted inputs that exploit parsing logic flaws in network services. An attacker positioned on the same subnet can leverage this flaw without needing valid authentication credentials if the vulnerable service listens on accessible ports or processes unauthenticated traffic types such as ICMP errors, DHCP requests, or malformed routing protocol updates. The ability of an insider threat actor or a compromised host within the LAN to trigger this condition underscores the risk posed by lateral movement scenarios where initial foothold has been established but privilege escalation is not immediately feasible.
Mitigation strategies must address both immediate remediation and long-term architectural resilience. The primary defense involves applying vendor-provided firmware updates that patch the specific memory handling routines responsible for the boundary check failure. Organizations should prioritize updating affected UniFi gateway models to versions where this logic error has been corrected with proper bounds checking mechanisms implemented in the source code. In scenarios where immediate patching is not possible due to operational constraints, network segmentation becomes a critical compensating control. By isolating the vulnerable devices behind firewalls that restrict inbound traffic from untrusted zones or by implementing strict access control lists on adjacent switches, administrators can limit the attack surface available to potential exploiters. Additionally, deploying intrusion detection systems tuned for anomalous packet patterns associated with buffer overflow attempts may provide early warning indicators of exploitation activity. Regular vulnerability scanning and continuous monitoring of device health metrics are essential to detect crashes resulting from such exploits quickly, ensuring rapid recovery and minimizing downtime impact on critical network services.