Annoying DNS queries with @rbl operator

[ne20002]

Describe the bug

Using a pihole in my network I realized that the rbl queries from Modsecurity are doing additional dns queries with the search domain (from resolv.conf) added.
This happens only for @rbl queries (or maybe modsecurity in general). It does not happen from other containers in the pod nor any other system in my network.

I use the owasp/modsecurity-crs:nginx container from Docker hub.

Expected behavior

The additional queries are not done.

[dune73]

That would be 0x42.ch in your case?

[ne20002]

Yes

[dune73]

Do you happen to know if the apache / ModSec2 docker container has the same problem?

[ne20002]

No, sorry. I only use the Nginx version.

[airween]

@ne20002 thanks for the report.

Could you provide an example, how can I try the explained behavior?

It does not happen from other containers in the pod nor any other system in my network.

This means the "vanilla" ModSecurity instance does not do this?

[ne20002]

This means the "vanilla" ModSecurity instance does not do this?

No, this just means that no other server in my network creates dns requests with the seen postfix. It's just the queries created by the @rbl checks.

This is the part in my config:

# xbl.spamhaus.org to block malicious/infected ips
SecRule IP:PREVIOUS_RBL_CHECK "@eq 1" "phase:1,id:910201,t:none,pass,nolog,skipAfter:END_RBL_LOOKUP"
  
SecRule REMOTE_ADDR "@rbl xbl.spamhaus.org" \
   "phase:1,id:910202,\
    t:none,pass,nolog,auditlog,\
    msg:'RBL Match for SPAM Source',\
    tag:'AUTOMATION/MALICIOUS',\
    severity:'CRITICAL',\
    setvar:'tx.msg=%{rule.msg}',\
    setvar:'tx.lfi_score=+%{tx.critical_anomaly_score}',\
    setvar:'tx.inbound_anomaly_score_pl1=+%{tx.critical_anomaly_score}',\
    setvar:ip.spammer=1,\
    expirevar:ip.spammer=86400,\
    setvar:ip.previous_rbl_check=1,\
    expirevar:ip.previous_rbl_check=86400,\
    skipAfter:END_RBL_CHECK"

SecAction "phase:1,id:910203,\
    t:none,nolog,pass,\
    setvar:ip.previous_rbl_check=1,\
    expirevar:ip.previous_rbl_check=3600"

SecMarker END_RBL_LOOKUP

SecRule IP:SPAMMER "@eq 1" \
    "phase:1,id:910204,\
    t:none,pass,nolog,auditlog,\
    msg:'Request from Known SPAM Source (Previous RBL Match)',\
    tag:'AUTOMATION/MALICIOUS',\
    severity:'CRITICAL',\
    setvar:'tx.msg=%{rule.msg}',\
    setvar:'tx.lfi_score=+%{tx.critical_anomaly_score}',\
    setvar:'tx.inbound_anomaly_score_pl1=+%{tx.critical_anomaly_score}'"

SecMarker END_RBL_CHECK

[fzipi]

Who can spot the typos here? https://github.com/owasp-modsecurity/ModSecurity/blob/v3/master/src/operators/rbl.h#L70-L76

[fzipi]

Tip: lines 74 and 76.

[fzipi]

Don't know if it solves this, but it is definitely broken.

[fzipi]

So, not really fixing this, but #3127.

[airween]

@ne20002 could you check again with current master branch?

[fzipi]

It might be difficult for @ne20002 if he is using pods for this, as the container is not updated with the new code from master.

@airween Maybe we can do a quick build and use the secrule he posted above with a simple curl test? From the source code, debug information is being printed with level 4 or up.