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Troubleshooting

Monitoring with cscli​

cscli metrics expose minimal metrics about the AppSec Component:

  • Number of requests processed and blocked by the component/data source
  • Number of triggers of each individual rules
Appsec Metrics:
╭───────────────────┬───────────┬─────────╮
│   Appsec Engine   │ Processed │ Blocked │
├───────────────────┼───────────┼─────────┤
│ myAppSecComponent │ 1.30k     │ 312     │
╰───────────────────┴───────────┴─────────╯

Appsec 'myAppSecComponent' Rules Metrics:
╭────────────────────────────────────┬───────────╮
│              Rule ID               │ Triggered │
├────────────────────────────────────┼───────────┤
│ crowdsecurity/vpatch-CVE-2017-9841 │ 38        │
│ crowdsecurity/vpatch-env-access    │ 274       │
╰────────────────────────────────────┴───────────╯

The prometheus metrics are more detailed, detailing analysis time for each request, along with detailed processing time for inband and out-of-band rule groups.

They can be seen in the dedicated grafana dashboard.

You can also inspect an AppSec rule directly with cscli appsec-rules inspect <rule_name> to see the amount of requests that were blocked by the rule.

Enabling Debug in the AppSec Component​

Debugging configuration is cascading in the AppSec Component.

Setting log_level to debug or trace in the acquisition config section or the AppSec config will enable debug logging for the whole AppSec Component. You can also set debug to true directly in an AppSec rule.

When enabling debug at acquisition or AppSec config level:

  • load time debug will be enabled, such as information regarding the translation of the rule to SecRule format.
  • runtime debug will be enabled for all the rules loaded by the AppSec Component / AppSec config.

When enabling debug directly at the appsec rule level, only runtime evaluation information of the rule will be displayed, such as:

DEBU[2023-12-06 15:40:26] Evaluating rule                               band=inband name=appseclol rule_id=2145145579 type=appsec uuid=adc5ffc4-6080-432c-af93-7c76c79afc25
DEBU[2023-12-06 15:40:26] Expanding arguments for rule                  band=inband name=appseclol rule_id=2145145579 type=appsec uuid=adc5ffc4-6080-432c-af93-7c76c79afc25 variable=REQUEST_URI
DEBU[2023-12-06 15:40:26] Transforming argument for rule                band=inband name=appseclol rule_id=2145145579 type=appsec uuid=adc5ffc4-6080-432c-af93-7c76c79afc25
DEBU[2023-12-06 15:40:26] Arguments transformed for rule                band=inband name=appseclol rule_id=2145145579 type=appsec uuid=adc5ffc4-6080-432c-af93-7c76c79afc25
DEBU[2023-12-06 15:40:26] Matching rule                                 band=inband key= name=appseclol rule_id=2145145579 type=appsec uuid=adc5ffc4-6080-432c-af93-7c76c79afc25 variable_name=REQUEST_URI
DEBU[2023-12-06 15:40:26] Evaluating operator: MATCH                    arg=/rpc2 band=inband name=appseclol operator_data=/rpc2 operator_function=@endsWith rule_id=2145145579 type=appsec uuid=adc5ffc4-6080-432c-af93-7c76c79afc25
DEBU[2023-12-06 15:40:26] Executing disruptive action for rule          action=deny band=inband name=appseclol rule_id=2145145579 type=appsec uuid=adc5ffc4-6080-432c-af93-7c76c79afc25
DEBU[2023-12-06 15:40:26] Rule matched                                  band=inband name=appseclol rule_id=2145145579 type=appsec uuid=adc5ffc4-6080-432c-af93-7c76c79afc25
DEBU[2023-12-06 15:40:26] Finish evaluating rule                        band=inband name=appseclol rule_id=2145145579 type=appsec uuid=adc5ffc4-6080-432c-af93-7c76c79afc25

Authenticating with the AppSec Component​

note

We are assuming the AppSec engine is running on 127.0.0.1:7422. See installation directives

Create a valid API Key

cscli bouncers add appsec_test -k this_is_a_bad_password

Emit a request to the AppSec Component

curl -I -X POST localhost:7422/ -i -H 'x-crowdsec-appsec-api-key: this_is_a_bad_password' -H 'x-crowdsec-appsec-ip: 42.42.42.42' -H 'x-crowdsec-appsec-uri: /test' -H 'x-crowdsec-appsec-host: test.com' -H 'x-crowdsec-appsec-verb: GET' 
HTTP/1.1 200 OK
Date: Tue, 05 Dec 2023 19:37:56 GMT
Content-Length: 18
Content-Type: text/plain; charset=utf-8

If you receive a 200 OK, you can authenticate to the AppSec Component. If the component is misconfigured or your API key is invalid, you will receive a 401 Unauthorized:

curl -I -X POST localhost:7422/ -i  -H 'x-crowdsec-appsec-api-key: meeh' -H 'x-crowdsec-appsec-ip: 42.42.42.42' -H 'x-crowdsec-appsec-uri: /test' -H 'x-crowdsec-appsec-host: test.com' -H 'x-crowdsec-appsec-verb: GET'          
HTTP/1.1 401 Unauthorized
Date: Tue, 05 Dec 2023 19:38:51 GMT
Content-Length: 0

Ensuring your rule(s) are loaded​

Crowdsec will show on startup all the rules that are installed (even if they are not used by any active appsec-config). Seeing a rule here does not mean it will be used by the AppSec Component, depending on the appsec-config you are using:

...
INFO[2023-12-06 14:58:19] Adding crowdsecurity/vpatch-CVE-2023-40044 to appsec rules 
INFO[2023-12-06 14:58:19] Adding crowdsecurity/vpatch-CVE-2023-42793 to appsec rules 
INFO[2023-12-06 14:58:19] loading acquisition file : ...

Testing a given rule​

We can create a skeleton environment with:

  • acquisition config that is going to load your test AppSec config
  • appsec config to load the test rule
  • the test rule itself

/etc/crowdsec/acquis.d/test_appsec.yaml

mkdir -p /etc/crowdsec/acquis.d/
cat > /etc/crowdsec/acquis.d/test_appsec.yaml <<EOF
name: test_appsec
listen_addr: 127.0.0.1:4243
appsec_config: crowdsecurity/test-appsec
source: appsec
labels:
  type: appsec
EOF

/etc/crowdsec/appsec-config/test_appsec_config.yaml

mkdir -p /etc/crowdsec/appsec-configs/
cat > /etc/crowdsec/appsec-configs/test_appsec_config.yaml <<EOF
name: crowdsecurity/test-appsec
default_remediation: ban
#log_level: debug
inband_rules:
 - crowdsecurity/test-rule
EOF

/etc/crowdsec/appsec-rules/test-rule.yaml

mkdir -p /etc/crowdsec/appsec-rules/
cat > /etc/crowdsec/appsec-rules/test-rule.yaml <<EOF
name: crowdsecurity/test-rule
description: "Detect test pattern"
rules:
  - zones:
    - URI
    transform:
    - lowercase
    match:
      type: contains
      value: this-is-a-appsec-rule-test
EOF

When starting crowdsec, you will see the following lines in the logs:

time="2023-12-20 13:39:29" level=info msg="loading inband rule crowdsecurity/test-rule" component=appsec_config name=crowdsecurity/test-appsec type=appsec
time="2023-12-20 13:39:29" level=info msg="Loaded 1 inband rules" component=appsec_config name=crowdsecurity/test-appsec type=appsec
time="2023-12-20 13:39:29" level=info msg="Created 1 appsec runners" name=test_appsec type=appsec
time="2023-12-20 13:39:29" level=info msg="Starting processing data"
time="2023-12-20 13:39:29" level=info msg="1 appsec runner to start" name=test_appsec type=appsec
time="2023-12-20 13:39:29" level=info msg="Starting Appsec server on 127.0.0.1:4243/" name=test_appsec type=appsec
time="2023-12-20 13:39:29" level=info msg="Appsec Runner ready to process event" name=test_appsec runner_uuid=846db2c6-4089-487e-a40e-6c778e5e125b type=appsec

Interacting with the AppSec Component​

To test that the AppSec Component is working correctly, you can send requests directly to it. A few things to know:

  • To query the AppSec Component, you need to have a valid remediation component API Key
  • The AppSec Component expects to receive some of the elements in specific headers

We are going to test that the AppSec Component detects correctly CVE-2023-42793, which is part of the virtual patching collection, that should be installed for this to work (see cscli appsec-rules list). This rule is pretty straightforward and detects requests to an URI ending with /rpc2:

cat /etc/crowdsec/appsec-rules/vpatch-CVE-2023-42793.yaml

name: crowdsecurity/vpatch-CVE-2023-42793
description: "Detect CVE-2023-42793"
rules:
  - zones:
    - URI
    transform:
    - lowercase
    match:
      type: endsWith
      value: /rpc2
labels:
  type: exploit
  service: http
  confidence: 3
  spoofable: 0
  behavior: "http:exploit"
  label: "JetBrains Teamcity auth bypass (CVE-2023-42793)"
  classification:
   - cve.CVE-2023-42793
   - attack.T1595
   - attack.T1190
   - cwe.CWE-288

To be able to communicate with the AppSec Component, let's create a bouncer API Key:

cscli bouncers add appsec_test -k this_is_a_bad_password

We can now query our AppSec Component (we're assuming here that it runs on the default 127.0.0.1:7422, see the listen_addr parameter of the acquisition config):

▶ curl -X POST localhost:7422/ -i -H 'x-crowdsec-appsec-ip: 42.42.42.42' -H 'x-crowdsec-appsec-uri: /rpc2' -H 'x-crowdsec-appsec-host: google.com' -H 'x-crowdsec-appsec-verb: POST' -H 'x-crowdsec-appsec-api-key: this_is_a_bad_password'
HTTP/1.1 403 Forbidden
Date: Tue, 05 Dec 2023 11:17:51 GMT
Content-Length: 16
Content-Type: text/plain; charset=utf-8

{"action":"ban"}

And we see the alert appearing in crowdsec.log :

...
INFO[2023-12-05 12:17:52] (test) alert : crowdsecurity/vpatch-CVE-2023-42793 by ip 42.42.42.42
...

And in cscli alerts list :

╭────┬────────────────┬─────────────────────────────────────┬─────────┬────┬───────────┬───────────────────────────────╮
│ ID │     value      │               reason                │ country │ as │ decisions │          created_at           │
├────┼────────────────┼─────────────────────────────────────┼─────────┼────┼───────────┼───────────────────────────────┤
│ 1  │ Ip:42.42.42.42 │ crowdsecurity/vpatch-CVE-2023-42793 │         │    │           │ 2023-12-05 11:17:51 +0000 UTC │
╰────┴────────────────┴─────────────────────────────────────┴─────────┴────┴───────────┴───────────────────────────────╯

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