Shell script for monitoring certificates emitted for a domain via Certificate Transparency logs
This script compares known certificates (stored locally) and registered certificates logged in public Certificate Transparency logs. It uses certspotter API and can retrieve certificates directly from host when it finds a registered certificate not already known.
Output and exit follow Nagios plugins development guidelines, making it suitable for integration in monitoring software such as Nagios, icinga, shinken, ...
Syntax of this script mainly inspired by check_ssl_cert, by Matteo Corti.
This script is free software, licensed as GPLv3.
Usage: check_ct_logs -H domain -d certificate_directory [-a API_KEY -g -A "184.108.40.206/example.com test.example.com" -i -v -V -h] This script compares known certificates (stored locally) and registered certificates logged in public Certificate Transparency logs. It uses certspotter API, from https://certspotter.com Arguments: -H, --hostname domain name to check -d, --certificate-directory where to find known certificates (PEM encoded) Options: -h, --help print this information and exits -a, --api-key CertSpotter API key. Needed if you do checks on a regular basis. Get one on : https://sslmate.com/signup?for=certspotter_api -c, --certspotter Certspotter API URL. Defaults to https://api.certspotter.com/v1/issuances But you can change to your instance if you run certspotter locally (see https://github.com/SSLMate/certspotter ) -i, --include-subdomains if set, the include subdomains option is set this will search for the hostname and all subdomains -g, --get-from-host if set, tries to contact host on port 443 to retrieve certificate from there if there is a registered certificate not known locally. -A, --addresses IP or DNS addresses to contact to retrieve certificate when '-g' is set. If not set, use argument from -H. For each address, server name can be specified after '/' : IP/server_name. -v, --verbose verbose output (can be specified more than once) -V, --version print script version and exit Examples: check_ct_logs -H test.example.com -d . check_ct_logs -H example.com -d . -i -g -A "example.com 10.0.0.5/dev.example.com 10.0.0.8/dev.example.com"
Just put this script along your other checks, and put known certificates in a
directory that your monitoring software can read. If you use the
option, the monitoring software should also be allowed to write to this directory.
If you plan to use it for monitoring, you should get an API key for cert spotter (free up to 1000 queries / hour)
CRITICAL : what to do ?
If the script answers that it found a certificate in certificate transparency logs that you didn't expect, try :
- running the same script with
-voption to know which certificate is missing or with
-v -vto print debug output (debugging certificate download)
- search on crt.sh the certificate (check_ct_logs gives you
- investigate : who delivered this certificate ? Who got it ? Should you revoke it ?
Please report bugs to https://github.com/Samuel-BF/check_ct_logs