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TLS Authentication

Overview#

In addition to the standard login/password (for agents) or API key (for bouncers), crowdsec also supports TLS client authentication for both.

This allows to bypass the requirement of generating login/password or API keys before adding a new agent or bouncer to your setup (this is especially useful if you are using any kind of auto-scaling and agents or bouncers can appears at anytime).

Configuration#

The TLS authentication is configured in the api.server.tls section of the configuration for LAPI and in /etc/crowdsec/local_api_credentials.yaml for the agents.

Please refer to the documentation of each bouncer to see how to configure them.

Revocation checking#

Crowdsec will perform both OCSP and CRL revocation check.

CRL check#

You can provide a path to a CRL file to crowdsec for revocation checking.

The revocation check will be skipped if the CRL file is invalid or has expired.

If no CRL file is provided, the check will also be skipped.

The result of the check is kept in cache according to the api.server.tls.cache_expiration configuration.

The CRL file is read each time the check is performed, so you can update it with a cronjob without needing to reload crowdsec.

OCSP check#

If the certificate contains an OCSP URL, crowdsec will make a query to the OCSP server to check for the revocation status.

The result of the check is kept in cache according to the api.server.tls.cache_expiration configuration.

If the OCSP server returns a malformed response, this check will be ignored.

Example#

PKI creation#

For this example, we will be creating our PKI with cfssl directly on the machine where crowdsec is running. In production, you will want to use your existing PKI infrastructure for obvious security reasons.

For the sake of simplicity, we will be using the same CA for the server and client certificates (in production, you will likely use differents CAs).

We will need some configuration files for cfssl.

First, we need to define some profiles for our cert in profiles.json:

{    "signing": {      "default": {        "expiry": "8760h"      },      "profiles": {        "intermediate_ca": {          "usages": [              "signing",              "digital signature",              "key encipherment",              "cert sign",              "crl sign",              "server auth",              "client auth"          ],          "expiry": "8760h",          "ca_constraint": {              "is_ca": true,              "max_path_len": 0,               "max_path_len_zero": true          }        },        "server": {          "usages": [            "signing",            "digital signing",            "key encipherment",            "server auth"          ],          "expiry": "8760h"        },        "client": {          "usages": [            "signing",            "digital signature",            "key encipherment",             "client auth"          ],          "expiry": "8760h"        }      }    }  }

Then, ca.json will define our CA:

{  "CN": "CrowdSec Test CA",  "key": {    "algo": "rsa",    "size": 2048  },  "names": [  {    "C": "FR",    "L": "Paris",    "O": "Crowdsec",    "OU": "Crowdsec",    "ST": "France"  } ]}

Next, intermediate.json will define our intermediate cert:

{    "CN": "CrowdSec Test CA Intermediate",    "key": {      "algo": "rsa",      "size": 2048    },    "names": [    {      "C": "FR",      "L": "Paris",      "O": "Crowdsec",      "OU": "Crowdsec Intermediate",      "ST": "France"    }   ],   "ca": {    "expiry": "42720h"  }  }

Our server side certificate is defined in server.json:

{    "CN": "localhost",    "key": {      "algo": "rsa",      "size": 2048    },    "names": [    {      "C": "FR",      "L": "Paris",      "O": "Crowdsec",      "OU": "Crowdsec Server",      "ST": "France"    }    ],    "hosts": [      "127.0.0.1",      "localhost"    ]  }

Lastly, we will define our bouncer and agents certs:

{    "CN": "mybouncer",    "key": {      "algo": "rsa",      "size": 2048    },    "names": [    {      "C": "FR",      "L": "Paris",      "O": "Crowdsec",      "OU": "bouncer-ou",      "ST": "France"    }    ]  }
{    "CN": "myagent",    "key": {      "algo": "rsa",      "size": 2048    },    "names": [    {      "C": "FR",      "L": "Paris",      "O": "Crowdsec",      "OU": "agent-ou",      "ST": "France"    }    ]  }

We can now create our CA and the certs:

#generate the CAcfssl gencert --initca ./cfssl/ca.json 2>/dev/null | cfssljson --bare "/tmp/ca"#Generate an intermediate certificate that will be used to sign the client certificatescfssl gencert --initca ./cfssl/intermediate.json 2>/dev/null | cfssljson --bare "/tmp/inter"cfssl sign -ca "/tmp/ca.pem" -ca-key "/tmp/ca-key.pem" -config ./cfssl/profiles.json -profile intermediate_ca "/tmp/inter.csr" 2>/dev/null | cfssljson --bare "/tmp/inter"#Generate a server side certificatecfssl gencert -ca "/tmp/inter.pem" -ca-key "/tmp/inter-key.pem" -config ./cfssl/profiles.json -profile=server ./cfssl/server.json 2>/dev/null | cfssljson --bare "/tmp/server"#Generate a client certificate for the bouncercfssl gencert -ca "/tmp/inter.pem" -ca-key "/tmp/inter-key.pem" -config ./cfssl/profiles.json -profile=client ./cfssl/bouncer.json 2>/dev/null | cfssljson --bare "/tmp/bouncer"#Generate a client certificate for the agentcfssl gencert -ca "/tmp/inter.pem" -ca-key "/tmp/inter-key.pem" -config ./cfssl/profiles.json -profile=client ./cfssl/agent.json 2>/dev/null | cfssljson --bare "/tmp/agent"

Configuration#

We now need to update LAPI configuration to use our newly generated certificates by editing /etc/crowdsec/config.yaml:

api: server:   tls:    cert_file: /tmp/server.pem #Server side cert    key_file: /tmp/server-key.pem #Server side key    ca_cert_path: /tmp/inter.pem #CA used to verify the client certs    bouncers_allowed_ou: #OU allowed for bouncers      - bouncer-ou    agents_allowed_ou: #OU allowed for agents      - agent-ou

We also need to update our agent configuration to use a certificate to login to LAPI in /etc/crowdsec/local_api_credentials.yaml:

url: https://localhost:8081ca_cert_path: /tmp/inter.pem #CA to trust the server certificatekey_path: /tmp/agent-key.pem #Client keycert_path: /tmp/agent.pem #Client cert

Using the certificates#

Now when we restart crowdsec, we will see in the logs that a new agent was creating automatically:

INFO[26-04-2022 13:42:36] TLSAuth: no OCSP Server present in client certificate, skipping OCSP verification  component=tls-auth type=agentWARN[26-04-2022 13:42:36] no crl_path, skipping CRL check               component=tls-auth type=agentINFO[26-04-2022 13:42:36] client OU [agent-ou] is allowed vs required OU [agent-ou]  component=tls-auth type=agentINFO[26-04-2022 13:42:36] machine myagent@127.0.0.1 not found, create itINFO[26-04-2022 13:42:36] 127.0.0.1 - [Tue, 26 Apr 2022 13:42:36 CEST] "POST /v1/watchers/login HTTP/2.0 200 117.853833ms "crowdsec/v1.3.3-rc2-55-g0988e03a-darwin-0988e03ab8b77ad08874266cf623e71396a68c6c" "INFO[26-04-2022 13:42:36] client OU [agent-ou] is allowed vs required OU [agent-ou]  component=tls-auth type=agentINFO[26-04-2022 13:42:36] 127.0.0.1 - [Tue, 26 Apr 2022 13:42:36 CEST] "POST /v1/watchers/login HTTP/2.0 200 1.267458ms "crowdsec/v1.3.3-rc2-55-g0988e03a-darwin-0988e03ab8b77ad08874266cf623e71396a68c6c" "

We can see the agent with cscli:

$ cscli machines list------------------------------------------------------------------------------------------------------------------------------------------------- NAME               IP ADDRESS  LAST UPDATE           STATUS  VERSION                                                                  AUTH TYPE------------------------------------------------------------------------------------------------------------------------------------------------- myagent@127.0.0.1  127.0.0.1   2022-04-26T11:42:36Z  ✔️       v1.3.3-rc2-55-g0988e03a-darwin-0988e03ab8b77ad08874266cf623e71396a68c6c  tls-------------------------------------------------------------------------------------------------------------------------------------------------

We see that the agent name was automatically derived from the certificate Common Name and agent IP address.

We can simulate a bouncer request using curl:

$ curl --cacert /tmp/inter.pem --cert /tmp/bouncer.pem --key /tmp/bouncer-key.pem https://localhost:8081/v1/decisions/stream?startup=true{"deleted":[{"duration":"-18h13m35.223932s","id":38,"origin":"crowdsec","scenario":"crowdsecurity/http-cve-2021-41773","scope":"Ip","type":"ban","value":"23.94.26.138"}],"new":null}

Because this is the first time this "bouncer" makes a request to LAPI, a new bouncer will be automatically created in crowdsec database. As with the agent, the name of the bouncer is CN@IP:

$ cscli bouncers list---------------------------------------------------------------------------------------- NAME                 IP ADDRESS  VALID  LAST API PULL         TYPE  VERSION  AUTH TYPE---------------------------------------------------------------------------------------- mybouncer@127.0.0.1  127.0.0.1   ✔️      2022-04-26T11:45:25Z  curl  7.79.1   tls----------------------------------------------------------------------------------------

If we try to use the agent certificate with our fake bouncer, LAPI with return an error as the OU is not allowed for the bouncers:

$ curl --cacert /tmp/inter.pem --cert /tmp/agent.pem --key /tmp/agent-key.pem https://localhost:8081/v1/decisions/stream\?startup\=true{"message":"access forbidden"}

And in crowdsec logs:

ERRO[26-04-2022 13:47:58] invalid client certificate: client certificate OU ([agent-ou]) doesn't match expected OU ([bouncer-ou])  ip=127.0.0.1

Now, if we revoke the certificate used by the bouncer, crowdsec will reject any request made using this certificate:

#serials.txt contain the serial of the bouncer certificate$ cfssl gencrl serials.txt /tmp/inter.pem /tmp/inter-key.pem | base64 -D | openssl crl -inform DER -out /tmp/crl.pem

Let's update crowdsec config to make use of our newly generated CRL:

api: server:  tls:   crl_path: /tmp/crl.pem

Let's query the API again:

$ curl --cacert /tmp/inter.pem --cert /tmp/bouncer.pem --key /tmp/bouncer-key.pem https://localhost:8081/v1/decisions/stream\?startup\=true{"message":"access forbidden"}

And we can see in crowdsec logs that the request was denied:

ERRO[26-04-2022 14:01:00] TLSAuth: error checking if client certificate is revoked: could not check for client certification revokation status: client certificate is revoked by CRL  component=tls-auth type=bouncerERRO[26-04-2022 14:01:00] invalid client certificate: could not check for client certification revokation status: could not check for client certification revokation status: client certificate is revoked by CRL  ip=127.0.0.1