Coding agentCursorConfirmed
Story 11 of 15 in the Friday 13 November editionCursor details October extension incident and moves off Fireworks
Published on 14 November 2026 after a two-week forensic investigation, Cursor traced the 29 October malicious Claude Code extension cache poisoning to an access key exposed at Fireworks.
Edited by Ashutosh Shrivastava
14 Nov 2026, 09:50 IST · 1 min read
Cursor published its investigation into the 29 October 2026 security incident on 14 November: an attacker used a storage key exposed at Fireworks to read historical non-Privacy-Mode traces (affecting under 0.05% of users and exposing credentials for under 0.01%), pivoted into internal tools and cached tampered Anthropic.claude-code 2.1.312 and 2.1.313 builds for roughly 11 hours (reaching at most 5,000 users), prompting Cursor to move all inference off Fireworks.
Technical details
- Initial breach vector
- Cursor-issued read-only training bucket key exposed at Fireworks; non-Privacy-Mode traces (<0.05% of users)
- Tampered extension builds
- Anthropic.claude-code 2.1.312 and 2.1.313 on Cursor VS Code marketplace cache (~11h on 29 October; <=5,000 users)
- Containment and vendor action
- Last blocked attacker activity on 1 November; all inference and shared datasets cut off from Fireworks
Release details & context
Unaffected production systems and remediation steps
Cursor confirmed that Privacy Mode sessions, live inference traffic, customer code repositories, Cursor client binaries, release signing keys, Open VSX upstream packages, Cloud Agents and Grok Bot were never compromised.
Alongside rotating all internal credentials, rebuilding its extension marketplace and redeploying production infrastructure with external forensics support, Cursor advised anyone who installed the tampered 2.1.312 or 2.1.313 builds on 29 October to run its full remediation steps rather than merely uninstalling the extension.
Sources
- PrimaryCursor Blog: An update on our recent security incidentcursor.com
- On XCursor (@cursor_ai) security incident update on Xx.com
Cursor release timeline (7 launches tracked)
- Cursor adds DeepSeek V4.1 Flash across all reasoning effort tiers
Cursor added DeepSeek V4.1 Flash to its model selector, placing every effort tier on the CursorBench cost frontier at $0.60 to $0.98 per task.
- Cursor introduces Annotate to design mode for visual canvas editing
Cursor introduced Annotate to its design mode, enabling developers to visually mark up web pages to direct coding agents.
- Cursor removes compromised Claude Code extension versions after marketplace incident
Cursor pulled compromised Anthropic.claude-code builds 2.1.312 and 2.1.313 from its marketplace after an 11-hour window affecting up to 5k users.
- Cursor rebuilds Projects for multiplayer agent coordination
Cursor rolls out multiplayer Projects in beta so teammates and their coding agents share specs, task boards and conflict-aware context.