WebShield and empty User-Agent in request

Issue

WebShield logs contain the following entries.

• Lua error in error.log:

/var/log/imunify360-webshield/error.log

[error] 14353#14353: *2714153 lua entry thread aborted: runtime error: /opt/imunify360-webshield/nginx/lua/reqrouter.lua:15: attempt to concatenate field 'http_user_agent' (a nil value)
stack traceback:
coroutine 0:
/opt/imunify360-webshield/nginx/lua/reqrouter.lua: in function 'set_untrusted_uid_cookie'
/opt/imunify360-webshield/nginx/lua/reqrouter.lua:110: in function </opt/imunify360-webshield/nginx/lua/reqrouter.lua:62>, client: 1.2.3.4, server: _, request: "GET /?key=simple-request&domain=my-super-domain.com&action=upgrade&version=3.1.1 HTTP/1.1", host: "host.server.com"

• Code 500 in access.log:

/var/log/imunify360-webshield/access.log

1.2.3.4 - - [18/Oct/2022:19:48:29 +1000] "GET /?key=simple-request&domain=my-super-domain.com&action=upgrade&version=3.1.1 HTTP/1.1" 500 174 host.server.com "-" "-" WL:"1" "-" XFF:"-" CAPTCHA:"0" PEER:1.2.3.4

Environment

• Imunify360
• WebShield

Solution

This is a known problem that has already been fixed in the latest Imunify360 release. It is sufficient to install updates for Imunify360, using the steps described in the documentation.

Cause

The problem itself is related to the situation that under certain conditions, WebShield cannot correctly process a request with an empty User-Agent.

Useful links

• https://docs.imunify360.com/features/#webshield.
• https://docs.imunify360.com/update/.