Add Incident Response Plan (IRP) for vulnerability handling

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mkagenius

INCIDENT_RESPONSE.md

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+# Incident Response Plan (IRP)
+
+This document outlines how we handle security vulnerabilities. It is a living document. Reporters and stakeholders can use the phases below to understand where we are during an active incident.
+
+We support two disclosure strategies:
+
+- **Advisory With Patch** _(default)_: A fix is prepared privately and released alongside a public advisory.
+- **Advisory Early** _(rare)_: An advisory is published before a fix is available — used when the vulnerability is already public or actively exploited.
+
+---
+
+## Phase 1 — Triage
+_"We're investigating."_
+**Target: within 36 hours of report**
+
+- Acknowledge receipt to the reporter.
+- Reproduce and validate the vulnerability.
+- Assess severity:
+  - **Critical** — Active exploitation or data exposure. Drop everything.
+  - **High** — Exploitable, no known active exploitation.
+  - **Medium/Low** — Limited impact or requires unlikely conditions.
+- Create a draft [GitHub Security Advisory (GHSA)](https://docs.github.com/en/code-security/security-advisories).
+- Decide disclosure strategy (Advisory With Patch or Advisory Early).
+
+## Phase 2 — Containment
+_"We've identified the issue and are limiting its impact."_
+**Target: 1–7 days after triage**
+
+- Isolate affected systems or services (revoke keys, disable endpoints, pull images).
+- Preserve evidence (logs, snapshots) before making changes.
+- Scope impact: identify affected components, versions, and platforms.
+- Request a CVE via the GitHub advisory interface.
+- Communicate status to the reporter.
+
+## Phase 3 — Fix & Release
+_"We're working on a fix."_
+**Target: within 90 days of initial report**
+
+- Develop and test a patch.
+- At least 2 team members review and sign off.
+- Publish the GHSA and deploy the fix simultaneously.
+- _Advisory Early: update the existing public advisory with fix details._
+
+## Phase 4 — Disclosure
+_"The fix is live. Here's what happened."_
+**Target: same day as fix release**
+
+- Notify the reporter that the issue is resolved.
+- Credit the reporter (unless they prefer anonymity).
+- Verify the published advisory is accurate and complete.
+- We follow the industry-standard **90-day coordinated disclosure window**. If a fix cannot ship in 90 days, we coordinate with the reporter on a revised timeline.
+
+## Phase 5 — Post-Incident Review
+_"We're making sure this doesn't happen again."_
+**Target: within 2 weeks of resolution**
+
+- Document root cause, timeline, and actions taken.
+- Identify process or code improvements to prevent recurrence.
+- Update this plan if gaps were found.
+
+---
+
+## Contact
+
+Email: [hello@instavm.io](mailto:hello@instavm.io)
+
+## Reporting a Vulnerability
+
+See [SECURITY.md](SECURITY.md). **Do not open public issues.**