After you upgrade your device to Fireware v12.5.3, applications that generate HTTP HEAD requests that are handled by an HTTP-proxy (or HTTPS-proxy with content inspection enabled) might stall or time out. 

Antivirus update agents and other software downloaders that use HEAD requests to pre-verify content they need to download are more likely to be affected by this issue. 

WatchGuard Support has confirmed the following update agents are affected by this issue:

• ESET NOD32 AntiVirus

Create a packet filter policy to handle the traffic. For agents that require access to multiple FQDNs, add wildcard FQDNs to the To: field of the policy.