network where host.os.type == "windows" and network.protocol == "dns" and
/* Add new free SSL certificate provider domains here */
dns.question.name : ("*letsencrypt.org", "*.sslforfree.com", "*.zerossl.com", "*.freessl.org") and
/* Native Windows process paths that are unlikely to have network connections to domains secured using free SSL certificates */
process.executable : ("C:\\Windows\\System32\\*.exe",
"C:\\Windows\\System\\*.exe",
"C:\\Windows\\SysWOW64\\*.exe",
"C:\\Windows\\Microsoft.NET\\Framework*\\*.exe",
"C:\\Windows\\explorer.exe",
"C:\\Windows\\notepad.exe") and
/* Insert noisy false positives here */
not process.name : ("svchost.exe", "MicrosoftEdge*.exe", "msedge.exe")
Install detection rules in Elastic Security
Detect Connection to Commonly Abused Free SSL Certificate Providers in the Elastic Security detection engine by installing this rule into your Elastic Stack.
To setup this rule, check out the installation guide for Prebuilt Security Detection Rules(opens in a new tab or window).