What the investigation found
Cursor released on November 13 the findings of the investigation launched after the discovery, on October 29, of an unauthorized and malicious copy of the Anthropic Claude Code extension in its VS Code extension marketplace. According to the company, most customers were not affected by the incident: the maximum number of affected users is estimated at 5,000. Cursor says it contacted all those affected directly, one by one, to communicate the details concerning them.
The company also clarified the limits of the exposure: those using privacy mode did not suffer consequences for prompts and code. Among those not using it, the share of users whose tracking data on coding-agent paths was exposed remains below 0.05%. Cursor states that it identified these users and notified them individually, indicating that anyone who did not receive a notification is not part of this data set.
The attack chain and the response
The account provided by the source begins with a compromised Fireworks access key: with that key, the attackers exfiltrated data from Cursor's shared storage bucket and, through a small number of unredacted credentials, breached some of the company's SaaS tools. The access is said to have involved non-production code repositories, customer support data, and some user credentials; according to Cursor, less than 0.01% of customers were affected by this step.
Upon detecting the anomalies, Cursor disabled the compromised keys, rotated credentials, and cut off unauthorized access, shutting down some internal and product services as a precaution; these were later restored after verification. On October 29, according to the company's account, the attackers used stolen internal credentials to insert the altered version of the Anthropic Claude Code extension into the marketplace, where it remained available for about 11 hours. Cursor then removed the extension, temporarily suspended the marketplace, and worked with the cloud provider to shut down the attackers' servers. The source stresses that the incident does not involve Anthropic or Open VSX.
Guidance for users and unresolved issues
On October 30, Cursor published a security notice and informed the parties involved, helping to revoke and replace the exposed keys. Anyone who installed the compromised version, identified as versions 2.1.312 or 2.1.313 of the extension, must follow the instructions in the notice: merely uninstalling the extension, the company warns, is not enough to eliminate the risk entirely. After blocking the last attack attempt on November 1, Cursor declared the incident under control and announced increased monitoring and protection, committing to inform affected customers directly of any developments.
Some elements remain that the material does not clarify: it does not state how many user credentials were actually compromised, nor what specific actions are required beyond the procedure indicated in the notice. The timeline of the investigation after November 13 is also not disclosed, nor are any independent verifications. The available information is what Cursor released and the source reported, and it reflects the company's version of events.
