Third-Party Notification Validation

1. Prerequisites

Before starting this runbook, ensure the following:

• Third-party compromise notification received
• Incident ticket created
• Access to vendor inventory
• Access to asset inventory
• Access to threat intelligence sources
• Access to vendor management contacts
• Access to security advisories and public reporting

2. Step-by-Step Instructions

1. Identify Notification Source

   Determine the source of the notification.

   Common sources include:

   • Vendor security notification
   • Vendor trust centre advisory
   • Security mailing list
   • Threat intelligence provider
   • Government advisory
   • Regulatory notification
   • Public disclosure
   • Social media disclosure
   • News reporting
   • Customer notification
   • Internal security team

   Document the source.

2. Validate Notification Authenticity

   Verify:

   • Notification sender
   • Vendor domain ownership
   • Advisory authenticity
   • Security bulletin legitimacy
   • Supporting references

   Review:

   • Vendor trust centre
   • Official advisories
   • Public statements
   • Security bulletins

   Identify potential phishing, spoofing, or misinformation attempts.

   Document findings.

3. Identify Affected Third Party

   Determine:

   • Vendor name
   • Product name
   • Service name
   • Business owner
   • Vendor criticality

   Identify:

   • Whether the vendor is actively used
   • Whether the relationship is current
   • Whether the service remains operational

   Document findings.

4. Gather Incident Details

   Collect:

   • Incident summary
   • Date of compromise
   • Discovery date
   • Attack vector
   • Impact statement
   • Scope of compromise
   • Known affected products
   • Known affected versions

   Document all available details.

5. Collect Technical Information

   Gather:

   • CVEs
   • Indicators of Compromise (IOCs)
   • Vendor mitigation guidance
   • Vendor remediation guidance
   • Detection recommendations
   • Published attacker techniques

   Store references within the incident record.

6. Determine Organisational Exposure

   Identify:

   • Use of affected products
   • Use of affected services
   • Use of affected versions
   • Existing integrations
   • Existing trust relationships

   Determine:

   • Whether the organisation is potentially exposed
   • Whether exposure can be immediately ruled out

   Document findings.

7. Assess Severity

   Determine whether the event represents:

   • Advisory only
   • Vulnerability disclosure
   • Suspected compromise
   • Confirmed compromise
   • Active exploitation
   • Confirmed organisational exposure

   Assign an initial severity rating.

   Document rationale.

. Update Incident Record

Record:

- Notification source
- Validation results
- Vendor details
- Product details
- Exposure assessment
- Severity assessment
- Stakeholder notifications

Attach supporting evidence and references.

3. Post-Action

Upon completion:

• Ensure notification authenticity has been validated
• Ensure affected vendor and products have been identified
• Ensure exposure assessment has been completed
• Ensure severity assessment is documented
• Ensure incident ticket is updated

Contributor

Vishal Thakur GitHub: https://github.com/malienist

Contributed to the Arcana Incident Response Documentation Framework.