INSPECTING ARCHIVED INTELLIGENCE (OUTDATED VERSION).

Gmarket's Electronic Coupons Accidentally Leaked Personal Information

| 2026-10-31 18:18 HIGH LOW DATA BREACH
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Executive Summary
AI-generated
A security breach has been confirmed at Gmarket, an online shopping platform in South Korea, where some customers' e-coupon PIN numbers were found to have been used by a third party without their knowledge or consent. The incident occurred on October 30 when a user discovered that their purchased cultural product coupon had been used by someone else, and the company reported it to KISA, which is investigating along with Gmarket. As of now, only some customers' PIN numbers were found to have been registered and used without authorization, but the exact number of affected customers remains unknown. The attack works by exploiting a vulnerability in the e-coupon management system or external linking process, allowing an attacker to obtain unique PIN numbers that can be misused by others if not secured properly outside. Gmarket has taken emergency security measures and is investigating the extent of the data breach, while also strengthening its security management system to protect customer information and cooperating with related institutions to investigate the cause and scope of the incident.
Technical Mitigations AI-generated
• Block external unauthorized access routes to prevent further misuse of electronic coupons. • Verify user authentication and access rights during the process of using e-coupons stored by customers. • Strengthen security management system to protect customer information, focusing on PIN number retrieval route and actual usage records.
Intelligence Metadata
Actors / Malware / CVEs / Campaigns
Target & Sectors
Global Scope retailretail
Incident Timeline
‎October 30
Gmarket confirmed on October 30 that some customers' e-coupon PIN numbers were found to have been registered and used by someone other than themselves.
‎2026/10/31
Threat actors used unknown methods to obtain PIN numbers from customers' e-coupons stored by Gmarket, prompting the company's investigation and subsequent report to KISA.
organisation the Korea Internet & Security Agency
The company reported the incident to the Korea Internet & Security Agency (KISA) and stated that it had checked the use history of the e-coupons stored by customers.
organisation KISA
The company reported the incident to the Korea Internet & Security Agency (KISA) and stated that it had checked the use history of the e-coupons stored by customers.
organisation PIN
However, the exact method by which the PIN numbers were obtained by the attacker remains unknown.
Intelligence Sources
Dailysecu 2026-10-31