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Bug#1010771: suricata: recieve erros after adding rule list

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severity 1010771 normal
thanks

Hi Tim,

I just noticed you also included your suricata.yaml configuration file 
in your bug report. I think I found the cause of your problem.

Let's take a look at a problematic rule:

> 9/5/2022 -- 14:20:21 - <Error> -- [ERRCODE: SC_ERR_INVALID_SIGNATURE(39)] -
> error parsing signature "alert udp ![$SMTP_SERVERS,$DNS_SERVERS] any ->
> $DNS_SERVERS 53 (msg:"ET DNS DNS Lookup for localhost.DOMAIN.TLD";
> content:"|01|"; offset:2; depth:1; content:"|00 01 00 00 00 00 00|";
> distance:1; within:7; content:"|09|localhost"; fast_pattern; nocase;
> classtype:bad-unknown; sid:2011802; rev:6; metadata:created_at 2010_10_13,
> updated_at 2019_09_03;)" from file /var/lib/suricata/rules/suricata.rules at
> line 3806

So this rule alerts if the content patterns are found in traffic from 
source addresses that are _not_ in the ranges configured for SMTP and 
DNS servers (![$SMTP_SERVERS,$DNS_SERVERS]). These variables are 
referenced in the rule but -- since the rule author does not know what 
the IP addresses of these servers are in your network -- need to be 
configured elsewhere, namely in your suricata.conf. Here's the relevant 
snippet from yours:

[...]> %YAML 1.1
> ---
> vars:
>    # more specific is better for alert accuracy and performance
>    address-groups:
>      HOME_NET: "[192.168.0.0/16,10.0.0.0/8,172.16.0.0/12]"
>      HOME_NET: "[192.168.0.0/16]"
>      HOME_NET: "[10.0.0.0/8]"
>      HOME_NET: "[172.16.0.0/12]"
>      HOME_NET: "any"
>      EXTERNAL_NET: "!$HOME_NET"
>      EXTERNAL_NET: "any"
>      HTTP_SERVERS: "$HOME_NET"
>      SMTP_SERVERS: "$HOME_NET"
>      SQL_SERVERS: "$HOME_NET"
>      DNS_SERVERS: "$HOME_NET"
>      TELNET_SERVERS: "$HOME_NET"
>      AIM_SERVERS: "$EXTERNAL_NET"
>      DC_SERVERS: "$HOME_NET"
>      DNP3_SERVER: "$HOME_NET"
>      DNP3_CLIENT: "$HOME_NET"
>      MODBUS_CLIENT: "$HOME_NET"
>      MODBUS_SERVER: "$HOME_NET"
>      ENIP_CLIENT: "$HOME_NET"
>      ENIP_SERVER: "$HOME_NET"

So you are setting both SMTP_SERVERS and DNS_SERVERS to the same value 
as your HOME_NET, which here effectively is "any", i.e. any possible IP 
address. Note that each of these assignments of HOME_NET overwrites the 
previous setting, so the last one here counts.
Now, evaluating that configuration, the rule above is now requiring the 
source address to be _not_ any possible IP address, which is obviously a 
problem which leads to an error being reported:

> 9/5/2022 -- 14:20:21 - <Error> -- [ERRCODE: 
> SC_ERR_INVALID_SIGNATURE(39)] - Complete IP space negated. Rule
> address range is NIL. Probably have a !any or an address range that
> supplies a NULL address range
The solution is easy. Please set only one value for HOME_NET which 
correctly reflects your internal IP addresses and make sure that 
DNS_SERVERS and the others are also set accordingly. Did you just 
comment in all the examples [1] in the stock suricata.yaml file? These 
are just examples -- keeping the first one with the RFC1918 addresses is 
usually sufficient. Otherwise, setting these values is a typical step in 
Suricata initial configuration and baselining.

Note that the same applies to EXTERNAL_NET.

Please let me know if you have any more questions. Lowering the severity 
here since from what I can see this is not an issue with Suricata per se 
but rather related to configuration.

Best regards
Sascha


[1] https://github.com/OISF/suricata/blob/master/suricata.yaml.in#L19

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Bug#1010771: suricata: recieve erros after adding rule list Sascha Steinbiss <satta@debian.org> - 2022-05-11 07:10 +0200

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