The SANS Internet Storm Center (ISC) has updated its Domainname API, which provides a list of recently registered or discovered domains, a valuable resource for threat intelligence and security monitoring. Historically, the API returned a large dataset that often caused issues by truncating the list, limiting the completeness of the data retrieved. To address this, the API now supports partial data retrieval through parameters that specify date, search string, start record, and count, enabling users to paginate and filter results. The API returns data in XML by default, with JSON available via query parameters. To obtain the full dataset, ISC now recommends using a static file (https://isc.sans.edu/feeds/domaindata.json.gz) updated hourly, which contains the complete list of new domains. This static file approach reduces API load and ensures full data availability. The data includes domain names, associated IP addresses if known, first seen dates, anomaly scores, and reasons for scoring, such as high entropy indicating potentially suspicious domains. The data is sourced partly from Certificate Transparency logs, which may cause some older domains to appear as new if newly observed in certificates. The ISC explicitly states that this data is provided on a best-effort basis, is free to use with attribution, and is not recommended as a blocklist but rather as contextual information to enrich security logs and analysis. The API predates modern RESTful standards and is somewhat unconventional but functional. No security vulnerabilities or exploits are associated with this update, and the changes primarily improve data accessibility and reliability.

For European organizations, the updated Domainname API and static file feed provide enhanced access to timely and comprehensive data on newly registered or discovered domains, which can be critical for early detection of phishing, malware distribution, and other domain-based threats. By integrating this data into security information and event management (SIEM) systems, intrusion detection systems (IDS), or threat intelligence platforms, organizations can better contextualize suspicious network activity and domain lookups. The partial API retrieval method may require adjustments in automated data collection scripts, but the availability of a full static file mitigates this limitation. Since the data is not a blocklist and is provided on a best-effort basis, organizations should use it as a supplementary intelligence source rather than a definitive filter. There is no direct security risk introduced by this update; rather, it improves the reliability and usability of threat intelligence data. European entities focused on cybersecurity operations, incident response, and threat hunting stand to benefit from these improvements. The low severity reflects the absence of new vulnerabilities or attack vectors.

While this update does not introduce security vulnerabilities, European organizations should take specific steps to maximize the utility and reliability of the Domainname data: 1. Transition automated data ingestion processes to use the static file feed (https://isc.sans.edu/feeds/domaindata.json.gz) for full data access, reducing reliance on partial API calls and avoiding data truncation issues. 2. Implement robust parsing and validation of the JSON data to handle anomaly scores and domain metadata effectively, integrating this context into existing security monitoring tools. 3. Use the data to enrich logs and alerts rather than as a strict blocklist, avoiding false positives and operational disruptions. 4. Monitor updates from ISC regarding retention of historical data and adjust data storage policies accordingly to maintain relevant historical context. 5. Provide feedback to ISC if API limitations impact operational workflows, encouraging future improvements. 6. Combine ISC domain data with other threat intelligence sources to improve detection accuracy and reduce noise. 7. Ensure that security teams understand the data’s limitations and best-use scenarios to avoid overreliance on this single source. 8. Maintain awareness of certificate transparency logs and other domain registration monitoring services to complement ISC data.