Add SECURITY.md file

README.md

@@ -272,3 +272,8 @@ an external contributor could potentially exploit it to extract the PAT.
 
 The only benefit of a "classic" PAT is that it can be set to never expire.
 However, we believe this does not outweigh the significantly higher risk of "classic" PATs compared to fine-grained PATs.
+
+## Reporting vulnerabilities
+
+If you find a vulnerability, please report it to us!
+See [SECURITY.md](./SECURITY.md) for more information.

SECURITY.md

@@ -0,0 +1,8 @@
+# Security
+
+If you find a significant vulnerability, or evidence of one,
+please report it privately.
+
+We prefer that you use the [GitHub mechanism for privately reporting a vulnerability](https://docs.github.com/en/code-security/security-advisories/guidance-on-reporting-and-writing/privately-reporting-a-security-vulnerability#privately-reporting-a-security-vulnerability). Under the
+[main repository's security tab](https://github.com/coreinfrastructure/best-practices-badge/security), in the left sidebar, under "Reporting", click
+Advisories, then click "Report a vulnerability" to open the advisory form.