Security researchers from Pen Test Partners identified multiple vulnerabilities in Eurostar's public-facing AI chatbot, including weaknesses that allowed prompt injection, HTML injection, and manipulation of chat session IDs. These flaws could have enabled attackers to inject malicious content, trick the chatbot into revealing internal system prompts, and potentially hijack or replay chat sessions. The researchers initially reported the issues through Eurostar's vulnerability disclosure program but faced communication breakdowns due to changes in the reporting process, resulting in delayed remediation and confusion over the status of their report.
During the disclosure process, Eurostar's head of security accused the researchers of 'blackmail' after they followed up on their unacknowledged report, raising concerns about the company's handling of responsible vulnerability disclosure. While Eurostar eventually patched some of the reported flaws, the incident highlights the challenges of vulnerability reporting and the importance of clear communication channels between security researchers and organizations deploying AI-driven customer service tools.

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After the disclosure process, Eurostar eventually fixed at least some of the reported chatbot flaws. Reports indicate it was unclear whether all identified issues had been fully resolved.
During the disclosure process, Eurostar's head of security allegedly accused the Pen Test Partners researchers of blackmail rather than treating the report as a standard vulnerability disclosure. The accusation became a central controversy in the incident.
Starting June 11, 2025, the researchers reported the chatbot vulnerabilities through Eurostar's vulnerability disclosure process. Initial reports were missed or delayed, reportedly due in part to outsourced security handling and platform transition issues.
Pen Test Partners identified multiple vulnerabilities in Eurostar's public AI customer service chatbot, including prompt injection, HTML injection, and weak validation of conversation and message IDs. The flaws could allow manipulation of conversations, leakage of system prompts, and malicious content injection.
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