Fireworks AI's Second Breach Reached Customer Datasets and Unfinished Model Weights, the Data Companies Send to Train Their Own Models

The pitch for fine-tuning open models is that a company keeps its own data and its own model. Fireworks' latest disclosure shows the other side of that pitch: the proprietary datasets and half-trained weights have to sit somewhere, and at Fireworks some of them were reached by attackers.

What Fireworks disclosed#

Fireworks, which runs and fine-tunes open models for businesses, updated its security bulletin on November 9. Its first notice, on October 9, said only Fireworks-stored secrets, such as those used in evaluation jobs, were known to have been accessed. Since then, the company said, it has found impacts to account and billing information, and, "for a limited set of accounts," to secrets, datasets and incomplete models.

The new access came through a supplier. A third-party cloud provider that hosted Fireworks' research machines suffered a security incident on October 23. On October 24, the attacker used it to reach Fireworks development machines and run an unauthorised workload that led to further customer data impact. Fireworks says it detected the activity the same day and has not seen further evidence of successful access to the platform customers use since October 25.

Exposed data, according to Fireworks, includes resource metadata, billing information such as addresses, invoices, balances and credit usage, and for certain customers a subset of incomplete model weights and datasets. Fireworks says it does not store payment card numbers, and that it has detected no impact to its inference, Training SDK and Nexus products, which do not retain data by default.

Fireworks says the evidence points to a financially motivated group that sells stolen access to large language models to illicit routing gateways, a practice known as LLMjacking. It is working with Palo Alto Networks' Unit 42, has rotated credentials, isolated affected systems and, for now, disabled self-serve dataset uploads and downloads for batch inference and dataset-based training. BleepingComputer's account matches the bulletin.

Customers' reaction#

Fireworks has roughly 10,000 enterprise customers, Forbes reported. Two customers told Forbes they had already substantially moved their business off Fireworks, one describing a series of "very bad hacks" and criticising the company's communication; two others said they were unaware of any hacks. A Fireworks spokesperson told Bloomberg Law the company is "actively working with our customers to manage the incident, including Notion, Cursor and others."

Limits#

• The scope of the breach is Fireworks' own account, and its investigation is continuing; the company says it may find more.
• Fireworks has not said how many customers had datasets or model weights accessed, or which ones.
• We read Forbes' report through a syndicated copy and could see only the opening of Bloomberg Law's paywalled article.
• Fireworks first gave notice on October 9 and published this update on November 9.

Sources#

• Fireworks AI: Update on October 2026 security incident (November 9, 2026)
• BleepingComputer: Fireworks AI discloses new breach after cloud provider hack (November 9, 2026)
• Forbes via SyncAI: Fireworks cyberattack exposes customer data and AI models as fallout widens (November 9, 2026)
• Bloomberg Law: Nvidia-backed Fireworks AI discloses its second hack in weeks (November 9, 2026)