CVE-2026-77544 Overview
CVE-2026-77544 is an out-of-bounds write vulnerability affecting certain Ubiquiti UniFi gateway devices. A network-adjacent attacker can trigger the flaw without authentication or user interaction, causing a denial-of-service (DoS) condition on the affected device.
The issue is classified under [CWE-787] (Out-of-bounds Write) and impacts device availability. Ubiquiti disclosed the vulnerability in Security Advisory Bulletin 069.
Critical Impact
Unauthenticated remote attackers on the network can crash affected UniFi gateway devices, disrupting network connectivity for all clients behind the gateway.
Affected Products
- Ubiquiti UniFi gateway devices (specific models per vendor advisory)
- Refer to Ubiquiti Security Advisory Bulletin 069 for the impacted model and firmware list
Discovery Timeline
- 2026-09-22 - CVE-2026-77544 published to NVD
- 2026-09-22 - Last updated in NVD database
Technical Details for CVE-2026-77544
Vulnerability Analysis
CVE-2026-77544 is an out-of-bounds write flaw in firmware running on certain UniFi gateway devices. The gateway processes network input in a manner that writes data past the bounds of an allocated buffer. This memory corruption crashes the handling process or the device itself, producing a denial-of-service condition.
Because the flaw resides in a network-facing component, an attacker only needs reachability to the gateway to send the malformed input. No credentials, tokens, or user interaction are required to trigger the condition.
The issue affects availability only. Ubiquiti's advisory does not describe confidentiality or integrity impact, and there is no public evidence that the out-of-bounds write leads to code execution.
Root Cause
The root cause is missing or insufficient bounds validation on attacker-controlled input processed by the gateway's network stack. When crafted data exceeds the expected size, the vulnerable routine writes beyond the destination buffer and corrupts adjacent memory. This corruption terminates the affected process, resulting in device disruption.
Attack Vector
Exploitation requires network access to the UniFi gateway. An attacker on the same network segment, or one that can otherwise reach the device's listening service, sends crafted packets that trigger the out-of-bounds write. The device then enters a crash or restart loop, breaking connectivity for downstream clients.
No authenticated code paths, administrative privileges, or user actions are needed. Publicly available exploit code is not currently listed for this CVE.
See Ubiquiti Security Advisory Bulletin 069 for vendor-specific technical details.
Detection Methods for CVE-2026-77544
Indicators of Compromise
- Unexpected reboots, crashes, or watchdog restarts on UniFi gateway devices
- Sudden loss of WAN or LAN connectivity coinciding with anomalous inbound traffic
- Gateway system logs showing kernel panics, segmentation faults, or service termination events
Detection Strategies
- Monitor UniFi controller and syslog output for repeated gateway offline or process crash entries
- Alert on bursts of malformed or oversized packets directed at gateway management or service ports
- Correlate device availability drops with network flow records to identify potential trigger sources
Monitoring Recommendations
- Forward UniFi gateway logs to a centralized SIEM for continuous availability monitoring
- Track firmware versions across the UniFi fleet and flag devices running vulnerable builds
- Baseline normal packet rates and sizes toward gateway interfaces to detect exploitation attempts
How to Mitigate CVE-2026-77544
Immediate Actions Required
- Apply the firmware update referenced in Ubiquiti Security Advisory Bulletin 069 to all affected UniFi gateway devices
- Inventory UniFi gateway models and firmware versions to identify exposed devices
- Restrict management-plane and service-plane access to the gateway using ACLs and trusted subnets
Patch Information
Ubiquiti has published fixed firmware through Security Advisory Bulletin 069. Administrators should update affected UniFi gateway devices to the patched firmware release identified in the advisory. Use the UniFi Network application or device UI to verify current firmware and apply the update.
Workarounds
- Limit inbound network reachability to the gateway from untrusted segments until patching is complete
- Segment guest and untrusted VLANs so they cannot reach gateway management or vulnerable services
- Enable automatic firmware updates within the UniFi controller to reduce exposure windows on future advisories
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.