Help request about Log4j attack attempts and NGINX logs meaning

Maxim Dounin mdounin at
Wed Dec 29 18:29:51 UTC 2021


On Wed, Dec 29, 2021 at 03:55:35PM +0100, Mauro Tridici wrote:

> I have an old instance of NGINX (v.1.10.1) running as proxy 
> server on a dedicated hardware platform.
> Since the proxy service is reachable from internet, it is 
> constantly exposed to cyber attacks.
> In my particular case, it is attacked by a lot of Log4j attack 
> attempts from several malicious IPs.
> At this moment, an host intrusion detection system (HIDS) is 
> running and is protecting the NGINX server: it seems it is 
> blocking every malicious attack attempts.
> Anyway, during the last attack mail notification sent by the 
> HIDS, I noticed that the NGINX server response was “HTTP/1.1 
> 200” and I’m very worried about it.
> Log4j and Java packages are NOT installed on the NGINX server 
> and all the servers behind the proxy are not using Log4j.
> Could you please help me to understand the reason why the NGINX 
> server answer was “HTTP/1.1 200”!?
> You can see below the mail notification I received:
> Attack Notification.
> 2021 Dec 28 20:45:59
> Received From: “hidden_NGINX_server_IP” 
> >/var/log/nginx/access.log
> Rule: 100205 fired (level 12) -> "Log4j RCE attack attempt 
> detected."
> Src IP:
> Portion of the log(s):
> - - [28/Dec/2021:21:45:58 +0100] "GET 
> /?sulgz=${jndi:ldap://“hidden_NGINX_server_IP 
> <ldap://%E2%80%9Chidden_server_IP>" 
> <ldap://>} 
> HTTP/1.1" 200 3700 "-" "curl/7.64.0" “-"

As you can see from the log line, the request is to "/" with some 
additional request arguments ("?sulgz=...").  As unknown request 
arguments are usually ignored, it is no surprise that such a 
request results in 200.

Maxim Dounin

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