Healing Paper, the operator of South Korea's largest medical beauty platform Gangnam Unni, issued a public apology on September 7 confirming that personal data of nearly 220,000 customers had been exposed through abnormal access to an API interface.
What Data Was Leaked
The breach involved far more than basic identifiers. Exposed information included names, phone numbers, email addresses, birth dates, gender, residential locations, social media IDs, and IP addresses. More critically, it also revealed medical beauty consultation details such as requested procedures, hospital and doctor names, reasons for consultation, treatment progress, user-uploaded consultation photos, appointment times, completed procedures, visit records, and payment information. These records create a comprehensive profile of an individual's health status, appearance insecurities, spending patterns, and movement history, including highly private pre-procedure images that users would never want shared.
Of the affected users, roughly 160,000 were in South Korea and 60,000 overseas. The overseas group included 48,000 from Japan, 4,218 from Taiwan, 1,591 from Thailand, and 481 from mainland China.
How the API Became the Leak Point
The attack path was straightforward and did not require sophisticated techniques. On September 4, attackers abnormally accessed an API endpoint designed for querying consultation records. After Healing Paper blocked that path, the same actor attempted access via a different route the next day. The root cause was insufficient authentication checks and missing rate-limiting controls on backend APIs. Many platforms focus security efforts on the main website and user interface while leaving API endpoints with loose access controls, incomplete logging, and no real-time anomaly detection.
Secondary Risks After the Breach
Security experts in South Korea have warned of immediate follow-on threats. Attackers could use the detailed medical and appointment data to craft convincing phishing messages impersonating the platform or clinics, offering fake promotions or appointment reminders. Even more concerning is the potential for extortion, where victims are threatened with the release of their pre-procedure photos and treatment records unless they pay.
Remediation and Recommendations
Healing Paper has reported the incident to the Korea Internet & Security Agency, involved law enforcement, conducted a full system review, strengthened identity verification, and added abnormal access monitoring. Users can check their exposure status on the official site within 30 days of the announcement.
Security teams are advised to treat APIs with the same rigor as primary web applications: enforce strict authentication and least-privilege access, implement rate limiting and behavioral analytics on sensitive endpoints, integrate API logs into SIEM systems, and include API attack surfaces in regular penetration testing. Users who registered with Gangnam Unni or similar platforms should verify any unexpected messages claiming to be from the service or clinics through official channels before clicking links or providing information.
