CVE-2026-86134
watchguard fireware
Summary
A NULL pointer dereference vulnerability in the WatchGuard Fireware OS authentication process allows a remote, unauthenticated attacker to crash the management daemon by sending a specially request to the login interface, resulting in a denial of service.
Published 2026-09-30 · first seen here 2026-10-10
Analysis & write-ups
No technical write-up from a research team yet. Contact Zero checks Unit 42, Google/Mandiant, Microsoft, Talos, CrowdStrike, Rapid7, watchTowr and others several times a day, plus NVD and CISA reference links.
Where it shows in your logs
Edge or network appliance (firewall, VPN, gateway) · Denial of service medium confidence
Appliances usually run no EDR, so device logs, firewall flow logs and the vendor's integrity checker are often the only evidence. Get the logs off the box: attackers often wipe local logs.
What to look for
- Service crashes or restarts lined up with bursts of traffic from a few sources
- Configuration changes, new local admin accounts or new VPN users on the appliance
- Admin or VPN logins from unfamiliar IPs, especially VPS or hosting providers
- New outbound connections from the appliance's own IP (it should rarely start connections)
- Gaps in the appliance's logs, unexpected reboots or crashes, or logs that were cleared
Data sources
Appliance system and admin logs · ATT&CK DS0015 Application Log Content
- Sentinel
CommonSecurityLog (CEF from Fortinet, Palo Alto, Check Point, Cisco)Syslog- Splunk
Vendor add-ons: fortigate_event, pan:system, pan:config, cisco:asa, citrix:netscaler:syslog, f5:bigip:syslogChange.All_Changes- CrowdStrike
Falcon Next-Gen SIEM: third-party firewall / VPN connectors
Authentication and sessions · ATT&CK DS0028 Logon Session Creation / DS0002 User Account Authentication
- Sentinel
SigninLogsSecurityEvent (4624, 4625, 4648)DeviceLogonEventsIdentityLogonEvents_Im_Authentication- Splunk
Authentication.Authenticationpan:globalprotectVPN sourcetypes- CrowdStrike
UserLogonUserLogonFailed2Falcon Identity Protection events
Network connections · ATT&CK DS0029 Network Connection Creation / Network Traffic Flow
- Sentinel
DeviceNetworkEventsCommonSecurityLog (firewall)_Im_NetworkSession- Splunk
Network_Traffic.All_TrafficFirewall sourcetypes (pan:traffic, fortigate_traffic, cisco:asa)- CrowdStrike
NetworkConnectIP4NetworkReceiveAcceptIP4NetworkConnectIP6
A generic baseline worked out from the product type and weakness (CWE-476), not a detection. Check table and field names against your environment. Hunt queries for Sigma, Splunk, Sentinel and CrowdStrike are coming.