Incident Response Guide for a Zero-Day Exploit at an Inherited Retinal Disease Clinic

A suspected zero-day exploit can threaten patient privacy, clinic systems, and the availability of services used to assess and manage inherited retinal disease. Your response should combine a coordinated security investigation with clear clinical downtime procedures, so staff can protect patients while limiting further access to systems and protected health information (PHI).

Use this guide alongside your organization’s incident response, emergency operations, and privacy policies. Decisions about clinical care, evidence collection, and notification obligations should be made by the appropriate clinical, technical, privacy, and legal leads.

How should the clinic prepare and coordinate its incident response?

Before an incident, identify who can declare and lead the response, who can make clinical continuity decisions, and who will assess privacy and legal obligations. Include the clinic’s security or IT lead, privacy officer, clinical leadership, operations, legal counsel, communications staff, and relevant vendors or business associates. Give staff a clear, fast way to report suspicious activity without trying to investigate it themselves.

Maintain an up-to-date inventory of systems that support care and contain PHI. For an inherited retinal disease clinic, consider whether electronic health records, imaging and diagnostic systems, scheduling, communications, identity services, and connected medical devices rely on shared networks or vendors. Document service owners, escalation contacts, dependencies, and safe manual alternatives.

Prepare playbooks for detection, containment, evidence preservation, clinical downtime, recovery, and patient communication. Test them with realistic exercises that include loss of access to records or diagnostic systems. HIPAA requires covered entities to have procedures for responding to security incidents and contingency plans for emergencies affecting systems that contain electronic PHI. See the HHS summary of the HIPAA Security Rule and HHS guidance on security incident procedures.

Agree in advance on how to contact the software, hosting, network, and medical-device vendors; how to preserve their relevant records; and how they must notify the clinic of suspected incidents. Keep a current contact list that staff can access if email or the clinic’s usual network is unavailable.

How can staff detect and assess a suspected zero-day exploit?

Ask staff to promptly report unusual system behavior, unexpected login prompts, missing or altered records, unexplained device or application failures, suspicious messages, or alerts from security tools. A zero-day exploit may not match a known malware signature, so staff should not dismiss an alert simply because antivirus software reports no known threat.

Use endpoint detection and response (EDR), where available, to investigate unusual processes, changes to system files, unexpected remote connections, and activity across affected devices. Review network monitoring and authentication logs for unfamiliar connections, unusual login times, repeated failed attempts, new administrator accounts, or access from unexpected locations. Compare findings across related systems, while recognizing that a single indicator does not prove an exploit occurred.

Record when the activity began, which systems and accounts may be involved, what PHI or clinical services could be affected, and what the clinic knows versus what remains unconfirmed. Preserve alert details and report the concern through the incident-response channel. Do not delay escalation while waiting for a vendor or outside party to confirm that the vulnerability is a zero-day.

Have technical responders determine whether the activity indicates attempted or successful unauthorized access, use, disclosure, modification, or destruction of information, or interference with system operations. HHS describes these events as security incidents and says covered entities must identify and respond to suspected or known incidents, mitigate harmful effects where practicable, and document the incident and its outcome. See HHS guidance on the Security Incident Procedures standard.

Which evidence and system logs should be preserved?

Preserve relevant records as early as practicable, before routine log rotation or troubleshooting changes the available evidence. Potential sources include EDR alerts and endpoint telemetry, operating-system and application logs, authentication logs, identity-provider and multifactor-authentication records, firewall and network traffic records, DNS and remote-access logs, email security records, cloud-service audit trails, and audit logs from systems that create, receive, maintain, or transmit PHI.

Preserve the available time range before and after the suspected activity, and record each system’s clock settings and time zone. Keep original files or exports intact, restrict access to authorized responders, and document how evidence was collected, transferred, stored, and analyzed. Avoid wiping, reimaging, or rebooting a suspected device before responders decide whether doing so could destroy useful evidence; immediate patient safety or containment needs may require action, so coordinate those decisions with clinical and technical leads.

Maintain a forensic evidence chain of custody when formal evidence handling is appropriate. Record identifying details for each item, who collected or handled it, the date and time of each transfer, and where it was stored. NIST’s incident-response guidance recommends documenting evidence handling and maintaining chain-of-custody records when applicable. See NIST SP 800-61 Rev. 3.

Preserve incident-response notes as well as technical records: decisions made, actions taken, people contacted, systems isolated, and the reason for major changes. HIPAA’s Security Rule requires audit controls that record and examine activity in information systems containing or using electronic PHI. See the HHS audit protocol’s explanation of audit controls.

How can affected systems be contained without compromising patient care?

Containment should limit the attacker’s access and prevent the suspected exploit from spreading, while clinicians assess how changes could affect active care. The incident lead and clinical lead should coordinate decisions about disconnecting devices, disabling services, restricting accounts, or changing network access. Do not let staff improvise changes to clinical or medical-device systems without the appropriate technical and clinical oversight.

Use network segmentation to separate affected endpoints or services from unaffected parts of the clinic where feasible. Security staff may block suspicious traffic, disable compromised accounts or remote access, revoke exposed credentials, or isolate an endpoint from the network. If a device or application is essential to current care, consider a controlled alternative or restricted operation rather than an unplanned shutdown, subject to clinical judgment and the manufacturer’s guidance.

When no patch is available, reduce exposure with vendor-approved mitigations, such as limiting access to the vulnerable service, disabling it if safe, or increasing monitoring. CISA’s incident and vulnerability response playbooks describe isolation, access restrictions, configuration changes, and increased monitoring as possible mitigation approaches when patches are unavailable or cannot be applied immediately.

Tell staff which tools and services are unavailable, how to report urgent issues, and which approved alternatives to use. Keep a record of containment actions and reassess them as responders learn more. Protect any PHI handled through alternative workflows using approved access, storage, and communication practices.

What clinical downtime procedures should the clinic activate?

Activate the clinic’s clinical downtime procedures when affected systems are unavailable, unreliable, or unsafe to use. Clinical leadership should set priorities based on patient need and the services that remain available. For each activity, identify who can authorize it, how staff will communicate, and how the clinic will record decisions until normal systems return.

Procedures may include paper documentation or approved offline forms, a controlled method for checking essential patient and appointment details, alternative communication channels, and a process for tracking services that must be entered into the electronic record later. Secure completed forms and devices, limit access to authorized staff, and keep a log of who created, accessed, or transferred downtime records.

For imaging, diagnostic equipment, or other technology used in patient care, follow the clinic’s approved procedures and applicable manufacturer instructions. Clinicians should determine whether a planned service can safely continue, must be modified, or should be rescheduled or referred elsewhere. Do not substitute an unvalidated workaround for a diagnostic or clinical function.

HIPAA contingency planning includes procedures for continuing critical business processes while operating in emergency mode, as well as plans for data backup and restoration. See the HHS audit protocol for contingency-plan requirements and HHS guidance on contingency planning and post-incident review.

How should the clinic eradicate the exploit and safely restore systems?

Do not restore a system simply because it appears to be working again. First, technical responders should identify and address the entry point and any persistence or additional compromised accounts they can find. Follow vendor guidance for the affected product, apply a validated patch when available, or use an appropriate mitigation until a patch can be safely deployed.

Where necessary, rebuild affected systems from known-good sources rather than relying on an unverified cleanup. Reset credentials or tokens that may have been exposed, review administrator access, and check connected systems for related indicators. Preserve evidence before making changes that could remove it, when doing so does not create an unacceptable risk to patient safety or containment.

Use verified backup restoration: confirm that backups are usable and from a point before compromise, scan or otherwise assess them as appropriate, and restore first into a controlled environment. Test system integrity, security controls, connectivity, and critical workflows before returning systems to production. Confirm that the restored data is complete enough for the clinic’s needs and reconcile downtime records through a documented process.

Return systems to service in stages, with increased monitoring and a clear escalation path if suspicious activity recurs. HIPAA requires contingency procedures for restoring lost data and continuing critical processes in emergency mode; HHS also describes containment, eradication, recovery, and post-incident analysis as parts of a robust response. See HHS Security Rule guidance and the HHS ransomware fact sheet.

How should the clinic review privacy obligations and improve its response?

Involve the privacy officer and legal counsel promptly to assess whether PHI may have been accessed, acquired, used, or disclosed impermissibly. A suspected exploit or other security incident is not automatically a reportable breach. Under the HIPAA Breach Notification Rule, an impermissible use or disclosure of unsecured PHI is generally presumed to be a breach unless the clinic demonstrates a low probability that the PHI was compromised through the required risk assessment or an exception applies.

Document the assessment, including the types and amount of PHI involved, who may have received or accessed it, whether it was actually viewed or acquired, and steps taken to reduce risk. Review applicable business associate agreements, state law, contractual duties, and any other requirements that may apply. Do not make notification decisions based only on whether the clinic found evidence of data exfiltration; have qualified privacy and legal staff evaluate the facts.

If the incident is a breach of unsecured PHI, the HIPAA Breach Notification Rule may require notice to affected individuals, HHS, and in some cases the media. Individual notice must be provided without unreasonable delay and no later than 60 days after discovery. The applicable process depends on the breach circumstances and number of affected people; consult the HHS Breach Notification Rule guidance for requirements and reporting details.

After recovery, review what happened, how quickly staff reported it, whether detection and containment worked, whether downtime procedures protected patient care and PHI, and whether vendors met their response obligations. Update the risk analysis, response contacts, technical safeguards, training, and tested procedures based on documented findings. HHS explains that Security Rule compliance is an ongoing process that includes risk analysis and periodic evaluation; see HHS guidance on ongoing Security Rule evaluation.

In short, prepare roles and downtime workflows in advance, investigate suspicious activity promptly, preserve evidence, contain threats in coordination with clinical staff, restore only from verified sources, and have privacy and legal leads assess notification duties.

FAQs.

When should a suspected zero-day exploit be treated as a reportable security incident?

Report suspected activity internally under the clinic’s incident-response procedures as soon as staff identify it. HIPAA’s security incident definition includes attempted as well as successful unauthorized access, use, disclosure, modification, or destruction of information, or interference with system operations. That does not mean every suspected exploit is automatically a reportable breach to patients or HHS. The clinic’s privacy and legal leads should determine whether unsecured PHI was impermissibly used or disclosed and whether notification obligations apply. See HHS security incident guidance and the HHS Breach Notification Rule.

How can a clinic isolate compromised systems while maintaining essential patient care?

Coordinate containment with the incident lead and clinical leadership. Use network segmentation, access restrictions, account controls, or targeted endpoint isolation where appropriate, while activating clinical downtime procedures for services that are unavailable or unsafe to use. Clinicians should decide whether affected services can safely continue through an approved alternative, need modification, or must be rescheduled or referred. Record containment decisions and protect PHI used in downtime workflows.

Which logs should be preserved during a zero-day exploit investigation?

Preserve relevant EDR and endpoint records, operating-system and application logs, authentication logs, identity-provider and multifactor-authentication records, firewall and network data, DNS and remote-access logs, email security records, cloud audit trails, and audit logs from systems that handle PHI. Retain the relevant time range and time-zone details, restrict access, and document collection and transfers. Preserve original records where possible, and coordinate before wiping or reimaging suspected systems.

Who should assess privacy and notification obligations after a clinic cyber incident?

The clinic’s privacy officer and legal counsel should lead the assessment with input from security responders and relevant clinical or operational leaders. They should review what PHI may have been affected, whether an impermissible use or disclosure occurred, applicable HIPAA requirements, business associate agreements, and any other relevant legal or contractual duties. Consult the HHS breach notification guidance when evaluating whether notice is required.