feat: Support for detecting outbound connection to c2 servers with FQ… #2241

Nicolas-Peiffer · 2022-10-10T15:20:53Z

…DN domains and IP addresses.

What type of PR is this?

If contributing rules or changes to rules, please make sure to also uncomment one of the following line:

/kind rule-update

/kind rule-create

Any specific area of the project related to this PR?

Uncomment one (or more) /area <> lines:

/area rules

What this PR does / why we need it:

This is a modification and enhancement of the Falco rule outbound connection to c2 servers. The rule was only considering IP addresses as a list of C2 servers. The rule was not considering Domain names (FQDN).

Now the rule both considers FQDN and IP address. This is espacially convenient for public list of C2 servers with both FQDN and IP addresses and that can be found on the internet, like this one:
https://feodotracker.abuse.ch/downloads/ipblocklist_recommended.json

The new outbound connection to c2 servers rules is inspired by other outbound rules like:
https://github.com/falcosecurity/falco/blob/master/rules/falco_rules.yaml#L392

Which issue(s) this PR fixes:

No issue.

Special notes for your reviewer:

I am not sure that there is a user-facing change. Else I would say:
Rule: Adding support for detecting outbound connection to c2 servers with both FQDN domains and IP addresses.

Does this PR introduce a user-facing change?:

rule(Outbound Connection to C2 Server): Update the "Outbound connection to C2 server" rule to match both FQDN and IP addresses. Prior to this change, the rule only matched IP addresses and not FQDN.

poiana · 2022-10-10T15:21:02Z

Welcome @Nicolas-Peiffer! It looks like this is your first PR to falcosecurity/falco 🎉

jasondellaluce · 2022-10-10T19:45:47Z

/milestone 0.34.0

darryk10

Hi,
thanks for contributing :) I agree with your idea and it can be helpful to use public lists.
I added some comments to simplify the change without rewriting the overall rule.

darryk10 · 2022-11-04T11:02:49Z

rules/falco_rules.yaml

+#        - "57.ip-142-44-247.net"
+#  ```
+
+- rule: Outbound Connection to C2 Servers IPs and FQDNs


I honestly don't think we need to change the rule name since it's accurate as it is.
we can just add in the existent description that the rules match IPs and FQDN.
I would just update the rule condition as done to support fqdn as well

Hi, I agree with your suggestions. The name of the rule can stay the same (Outbound Connection to C2 Servers), as well as the output: field.

If you prefer, I can revert to the previous rule name.

Question: I understand you prefer this

desc: Detect outbound connection to command & control servers thanks to a list of IP addresses & a list of FQDN.

over this?

desc: > Detect outbound connection to command & control servers. For example, fetch a list of IP addresses and FQDN on this website: https://feodotracker.abuse.ch/downloads/ipblocklist_recommended.json.

I have no opinion on this one. I understand it is maybe better not to include a link to feodotracker.abuse.ch.

@Nicolas-Peiffer I'll go with this one

desc: Detect outbound connection to command & control servers thanks to a list of IP addresses & a list of FQDN.

I feel the desc you added is more a comment for the rule so since it is actually a useful comment I think you can add it on top fo the rule as a proper comment as done in other rules. What do you think?

darryk10 · 2022-11-04T11:07:24Z

@Nicolas-Peiffer can you also pls add something in the PR section for the release note?
Does this PR introduce a user-facing change?

Nicolas-Peiffer · 2022-11-04T16:24:57Z

@darryk10 I updated the release note.

And I cleaned my commits and modifed the rule taking into account your suggestions.

darryk10 · 2022-11-07T13:50:05Z

rules/falco_rules.yaml

+    outbound and 
+    ((fd.sip in (c2_server_ip_list)) or
+     (fd.sip.name in (c2_server_fqdn_list)))
+  output: Outbound connection to C2 server (command=%proc.cmdline connection=%fd.name user=%user.name user_loginuid=%user.loginuid container_id=%container.id image=%container.image.repository)


I think it would be also useful to print out fd.sip and fd.sip.name for troubleshooting and investigation.
WDYT?

I did not think of it but you are right about that enhancement of the output:.
However, I am not sure what is the behaviour if there is only an IP addresse or only an FQDN: would either %fd.sip.name or %fd.sip be blank in that case?

But indeed, we can consider something like this:

output: Outbound connection to C2 server domain=%fd.sip.name addr=%fd.sip (command=%proc.cmdline connection=%fd.name user=%user.name user_loginuid=%user.loginuid container_id=%container.id image=%container.image.repository)

or this (moving the parenthesis):

output: Outbound connection to C2 server (domain=%fd.sip.name addr=%fd.sip command=%proc.cmdline connection=%fd.name user=%user.name user_loginuid=%user.loginuid container_id=%container.id image=%container.image.repository)

We could also be more specific by adding a prefix c2_ like this: c2_domain=%fd.sip.name c2_addr=%fd.sip .
I have no particular preference.

I agree the option with c2_domain and c2_addr would be specific and clear so I would go in this direction.
I would also go for this output you mentioned

output: Outbound connection to C2 server (domain=%fd.sip.name addr=%fd.sip command=%proc.cmdline connection=%fd.name user=%user.name user_loginuid=%user.loginuid container_id=%container.id image=%container.image.repository)

As far as the empty fields goes I don't think it would be a problem if left empty but if you could do a quick test to see if all makes sense from your side would be awesome.
Thanks again

Okay no big deal with blank IP addresses or blank FQDN : falco will output <NA> if there are no values.

In the following, we can see c2_domain=<NA> c2_addr=46.101.90.205 because the rule was triggered only with the IP adress.

I am pushing the modification.

falco 18:25:57.134661204: Warning Outbound connection to C2 server (c2_domain=<NA> c2_addr=46.101.90.205 command =curl 46.101.90.205 connection=10.42.0.7:59170->46.101.90.205:80 user=<NA> user_loginuid=-1 container_id=62513c2 df2f2 image=<NA>) k8s.ns=default k8s.pod=tmp-shell container=62513c2df2f2

…DN domains and IP addresses. Signed-off-by: Nicolas-Peiffer <[email protected]> feat: Support for detecting outbound connection to c2 servers with FQDN domains and IP addresses. doc: add comment Fixing DCO append amend Signed-off-by: Nicolas-Peiffer <[email protected]> Revert to original C2 rule name Signed-off-by: Nicolas-Peiffer <[email protected]> modify comments on C2 rule Signed-off-by: Nicolas-Peiffer <[email protected]> comment Signed-off-by: Nicolas-Peiffer <[email protected]> clean comments Signed-off-by: Nicolas-Peiffer <[email protected]> clean comments Signed-off-by: Nicolas-Peiffer <[email protected]> modify stdout Signed-off-by: thedetective <[email protected]>

darryk10

LGTM
Thanks @Nicolas-Peiffer for the changes :)

poiana · 2022-11-10T07:34:04Z

LGTM label has been added.

Git tree hash: 5f7c82748c8021b8b6c1b7522d5284376eda23fd

jasondellaluce

/approve

leogr · 2022-12-15T11:45:07Z

Closing and reopening to trigger the CI
/close

poiana · 2022-12-15T11:45:10Z

@leogr: Closed this PR.

In response to this:

Closing and reopening to trigger the CI
/close

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

leogr · 2022-12-15T11:45:13Z

/reopen

poiana · 2022-12-15T11:45:16Z

@leogr: Reopened this PR.

In response to this:

/reopen

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

leogr · 2022-12-15T11:52:19Z

/approve

poiana · 2022-12-15T11:52:23Z

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: darryk10, jasondellaluce, leogr, Nicolas-Peiffer

The full list of commands accepted by this bot can be found here.

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poiana added release-note-none kind/rule-update dco-signoff: no kind/rule-create labels Oct 10, 2022

poiana requested review from Kaizhe and leodido October 10, 2022 15:20

poiana added the area/rules label Oct 10, 2022

poiana added size/M do-not-merge/contains-merge-commits labels Oct 10, 2022

Nicolas-Peiffer force-pushed the c2-srv-list-fqdn branch 2 times, most recently from 4393f71 to 59fc390 Compare October 10, 2022 16:01

poiana added dco-signoff: yes and removed dco-signoff: no do-not-merge/contains-merge-commits labels Oct 10, 2022

poiana added this to the 0.34.0 milestone Oct 10, 2022

darryk10 suggested changes Nov 4, 2022

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poiana assigned darryk10 Nov 4, 2022

poiana added do-not-merge/contains-merge-commits release-note and removed release-note-none labels Nov 4, 2022

Nicolas-Peiffer force-pushed the c2-srv-list-fqdn branch from 7b67fc8 to 83345fc Compare November 4, 2022 16:21

poiana removed the do-not-merge/contains-merge-commits label Nov 4, 2022

darryk10 reviewed Nov 7, 2022

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Nicolas-Peiffer force-pushed the c2-srv-list-fqdn branch from 83345fc to 3bfb8e0 Compare November 9, 2022 18:38

darryk10 approved these changes Nov 10, 2022

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poiana added the lgtm label Nov 10, 2022

leogr approved these changes Dec 15, 2022

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jasondellaluce approved these changes Dec 15, 2022

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poiana closed this Dec 15, 2022

poiana reopened this Dec 15, 2022

poiana merged commit 1f15af1 into falcosecurity:master Dec 15, 2022

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feat: Support for detecting outbound connection to c2 servers with FQ… #2241

feat: Support for detecting outbound connection to c2 servers with FQ… #2241

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feat: Support for detecting outbound connection to c2 servers with FQ… #2241

feat: Support for detecting outbound connection to c2 servers with FQ… #2241

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