docs: add security response process (external-secrets#3037)

Signed-off-by: Moritz Johner <beller.moritz@googlemail.com>

SECURITY.md

@@ -20,3 +20,7 @@ We learn about critical software updates and security threats from these sources
 
 1. GitHub Security Alerts
 2. [Dependabot](https://dependabot.com/) Dependency Updates
+
+## Security Incident Response
+
+Please follow the guide [SECURITY_RESPONSE.md](SECURITY_RESPONSE.md).

SECURITY_RESPONSE.md

@@ -0,0 +1,88 @@
+# Incident response
+
+This serves to define how potential security issues should be triaged, how
+confirmation occurs, providing the notification, and issuing a security advisory
+as well as patch/release.
+
+## Triage
+
+### Identify the problem
+
+Triaging problems allows maintainers to focus resources on the most critically
+impacting problems. Potential security problems should be evaluated against the
+following information:
+
+* Which component(s) of the project is impacted?
+* What kind of problem is this?
+  * privilege escalation
+  * credential access
+  * code execution
+  * exfiltration
+  * lateral movement
+* How complex is the problem?
+* Is user interaction required?
+* What privileges are required for this problem to occur?
+  * admin
+  * general
+* What is the potential impact or consequence of the problem?
+* Does an exploit exist?
+
+Any potential problem that has an exploit, permits privilege escalation, is
+simple, and does not require user interaction should be evaluated immediately.
+[CVSS Version 3.1](https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator) can be
+a helpful tool in evaluating the criticality of reported problems.
+
+### Acknowledge receipt of the problem
+
+Respond to the reporter and notify them you have received the problem and have
+begun reviewing it. Remind them of the [embargo policy](https://github.com/cncf/tag-security/blob/231b87f371274b2d68def2c6a35a719210836191/project-resources/templates/embargo-policy.md), and provide them
+information on who to contact/follow-up with if they have questions. Estimate a
+time frame that they can expect to receive an update on the problem. Create a
+calendar reminder to contact them again by that date to provide an update.
+
+### Replicate the problem
+
+Follow the instructions relayed in the problem. If the instructions are
+insufficient, contact the reporter and ask for more information.
+
+If the problem cannot be replicated, re-engage the reporter, let them know it
+cannot be replicated, and work with them to find a remediation.
+
+If the problem can be replicated, re-evaluate the criticality of the problem, and
+begin working on a remediation. Begin a draft security advisory.
+
+Notify the reporter you were able to replicate the problem and have begun working
+on a fix. Remind them of the [embargo policy](https://github.com/cncf/tag-security/blob/231b87f371274b2d68def2c6a35a719210836191/project-resources/templates/embargo-policy.md). If necessary, notify them of an
+extension (only for very complex problems where remediation cannot be issued
+within the project's specified window).
+
+#### Request a CVE number
+
+If a CVE has already been provided, be sure to include it on the advisory. If
+one has not yet been created, [GitHub functions as a
+CNA](https://docs.github.com/en/code-security/security-advisories/about-github-security-advisories#cve-identification-numbers)
+and allows you to request one as part of the security advisory process. Provide
+all required information and as much optional information as we can. The CVE
+number is shown as reserved with no further details until notified it has been
+published.
+
+## Notification
+
+Once the problem has been replicated and a remediation is in place, notify
+subscribed parties with a security bulletin (use [this template](https://github.com/cncf/tag-security/blob/231b87f371274b2d68def2c6a35a719210836191/project-resources/templates/embargo.md)) and the expected publishing date.
+
+## Publish and release
+
+Once a CVE number has been assigned, publish and release the updated
+version/patch. Be sure to notify the CVE group when published so the CVE details
+are searchable. Be sure to give credit to the reporter by *[editing the security
+advisory](https://docs.github.com/en/github/managing-security-vulnerabilities/editing-a-security-advisory#about-credits-for-security-advisories)*
+as they took the time to notify and work with you on the problem!
+
+### Issue a security advisory
+
+Follow the instructions from [GitHub to publish the security advisory previously
+drafted](https://docs.github.com/en/github/managing-security-vulnerabilities/publishing-a-security-advisory).
+
+For more information on security advisories, please refer to the [GitHub
+Article](https://docs.github.com/en/code-security/security-advisories/about-github-security-advisories).