CVE-2026-77558 Overview
CVE-2026-77558 is an out-of-bounds read vulnerability [CWE-125] affecting certain Ubiquiti UniFi gateway devices. A network-adjacent attacker without authentication can trigger the flaw to cause a denial of service (DoS) condition on the affected device. Ubiquiti disclosed the issue in Security Advisory Bulletin 069. The vulnerability impacts availability only, with no direct impact on confidentiality or integrity.
Critical Impact
An unauthenticated attacker with network access to a vulnerable UniFi gateway can disrupt device operation, taking down routing, firewalling, and connectivity services for downstream networks.
Affected Products
- Ubiquiti UniFi gateway devices (specific models listed in Ubiquiti Security Advisory Bulletin 069)
Discovery Timeline
- 2026-09-22 - CVE CVE-2026-77558 published to NVD
- 2026-09-22 - Last updated in NVD database
Technical Details for CVE-2026-77558
Vulnerability Analysis
The vulnerability is an out-of-bounds read [CWE-125] in the network-facing code path of affected UniFi gateway devices. When the device processes a crafted network input, it reads memory outside the bounds of an allocated buffer. This triggers a crash or unrecoverable state, resulting in denial of service.
The issue is remotely reachable over the network without authentication or user interaction. Attackers do not need credentials or physical proximity beyond network reachability to the gateway. Because UniFi gateways sit at the network perimeter, an availability failure disrupts routing, NAT, VPN, and firewall enforcement for all downstream clients.
Ubiquiti's advisory scopes the issue to gateway devices rather than the broader UniFi controller or access point ecosystem. Refer to the Ubiquiti Security Advisory Bulletin 069 for the definitive list of affected firmware versions and models.
Root Cause
The root cause is missing or insufficient bounds checking when parsing attacker-controlled network data. Reading past the intended buffer boundary accesses adjacent memory the parser did not allocate. On embedded network appliances, this typically triggers a process fault or watchdog-driven reboot.
Attack Vector
Exploitation requires only network reachability to the affected gateway. An attacker sends specially crafted traffic to a listening service on the device to trigger the out-of-bounds read. No authentication and no user interaction are required. The Ubiquiti advisory is the authoritative source for the affected protocol and service. Public proof-of-concept code is not currently available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.
Detection Methods for CVE-2026-77558
Indicators of Compromise
- Unexpected reboots, service restarts, or watchdog-triggered failovers on UniFi gateway devices.
- Gaps in gateway telemetry, syslog, or SNMP polling that align with malformed inbound packets.
- Repeated crash entries or segmentation faults in device diagnostic logs referencing network parsing components.
Detection Strategies
- Enable remote syslog forwarding from UniFi gateways to a centralized log platform and alert on repeated crash or restart events.
- Correlate gateway availability drops with upstream firewall or IDS logs showing anomalous inbound traffic patterns from a single source.
- Deploy network intrusion detection signatures for malformed packets targeting management or service ports exposed by UniFi gateways once Ubiquiti publishes protocol details.
Monitoring Recommendations
- Monitor gateway uptime with sub-minute polling to identify short outages caused by exploitation attempts.
- Track WAN-side connection attempts to administrative or service ports on UniFi gateways and alert on unusual sources.
- Baseline normal packet sizes and protocol behavior toward gateway services to identify anomalies indicative of crafted DoS payloads.
How to Mitigate CVE-2026-77558
Immediate Actions Required
- Apply the firmware update referenced in Ubiquiti Security Advisory Bulletin 069 to all affected UniFi gateway devices.
- Inventory all UniFi gateways in the environment and confirm firmware versions against the advisory.
- Restrict inbound network access to management and non-essential services on gateway WAN interfaces.
Patch Information
Ubiquiti has published fixed firmware for affected UniFi gateway devices. Consult Ubiquiti Security Advisory Bulletin 069 for the specific firmware versions that remediate CVE-2026-77558 and apply them through the UniFi Network application or device console.
Workarounds
- Block untrusted networks from reaching gateway management and service ports using upstream ACLs or perimeter firewall rules.
- Limit exposure of the affected service to trusted management VLANs and known administrator source addresses.
- Enable automatic device recovery and high-availability failover where supported to reduce the impact of induced crashes until patching is complete.
# Example: restrict WAN-side access to UniFi gateway management interfaces
# Replace <mgmt_subnet> and <wan_iface> with environment-specific values
iptables -A INPUT -i <wan_iface> -s <mgmt_subnet> -p tcp --dport 443 -j ACCEPT
iptables -A INPUT -i <wan_iface> -p tcp --dport 443 -j DROP
iptables -A INPUT -i <wan_iface> -p udp --dport 500 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
