Truth of Cursor's hack exposed: Fireworks leaked its API key, hackers breached the plugin store after accessing AI training logs.

Beating AI Flash News: Cursor has released the findings of its investigation into the earlier poisoning incident affecting the Claude Code plugin. After a two-week probe, the company discovered the attack originated from its AI service provider, Fireworks. According to Cursor, Fireworks leaked an access key granted by the company. Hackers used this key to copy historical Coding Agent operation logs stored by Cursor in shared storage. The data primarily came from 2025 user sessions that did not have privacy mode enabled, originally intended for model training. More seriously, some API keys in these records were not redacted. Using these credentials, hackers further breached some internal software services used by Cursor, accessing archived non-production code, customer support emails, product usage data, partial AI conversation summaries, and credentials users had submitted to support. On October 29, hackers used credentials stolen from Cursor internally to tamper directly with the extension store’s cache, distributing versions Claude Code 2.1.312 and 2.1.313 embedded with an SSH backdoor to users. The malicious versions were available for approximately 11 hours, with up to 5,000 users potentially downloading them. The upstream plugin marketplace Open VSX was not tampered with, and Anthropic’s official versions remained unaffected. Cursor disclosed that the leaked Coding Agent logs involved fewer than 0.05% of its users, with fewer than 0.01% of users having their API credentials exposed. Sessions with privacy mode enabled, customer code repositories, and production systems were not impacted. Cursor noted the last detection of hacker activity was on November 1, when it was successfully intercepted. The company has now notified affected users, fully ceased using Fireworks for inference requests, revoked its data access permissions, rotated internal credentials, and redeployed production infrastructure.