They don't agree.

Both companies gave public accounts of the incident: its timing, its scope, what the malware did, and Anthropic's denial that its own systems were breached. What neither had explained, according to press reports from October 30 to November 1, 2026, was the root cause, meaning how the attacker gained publishing access on Cursor's marketplace under Anthropic's extension ID. So the claim holds for the cause of the incident but not for the incident as a whole. This is a fast-moving story, and a fuller post-mortem could change the answer.

• Cursor said a malicious Claude Code extension, version 2.1.313, was live on its marketplace on October 29, 2026, for about 11 hours. It said at most 5,000 users were affected.
• Cursor published a security notice describing what the malicious code did: it tried to add an attacker's SSH key and open a reverse SSH tunnel.
• Anthropic's Felix Rieseberg said it was not a compromise of Anthropic's systems or employee laptops. He said an attacker used access to Cursor's marketplace to publish a tampered copy.
• Anthropic released version 2.1.314 without the malicious code.
• BleepingComputer, The Register and The Next Web reported that neither company had explained how the attacker published under Anthropic's extension ID.

1. Anthropic: That Claude Code extension compromise ... theregister.com
2. Cursor Confirms Anthropic Claude Code Extension Compromised bankinfosecurity.com
3. Official Claude Code Extension on Cursor Marketplace Trojanized with Persistent SSH Backdoor thehackernews.com
4. Cursor removes malicious Claude Code extension after SSH backdoor attempt csoonline.com
5. Trojanized Claude Code Extension Delivered Persistent SSH Backdoor to Developer Machines - StepSecurity stepsecurity.io
6. Anthropic denies breach as tampered Claude Code extension hits Cursor users thenextweb.com
7. Anthropic - Claude Code - Cursor - Panorays Threat Intelligence Report - Oct 2026 panorays.com
8. Anthropic hacked via Cursor to deliver remote access trojan to Claude developer laptops worldwide doublepulsar.com

The claim is contradicted by Cursor’s published incident explanation and Anthropic’s public clarification. However, those disclosures did not explain every aspect of the compromise: reporting on October 31, 2026 specifically noted that neither company had explained how the attacker obtained marketplace access. That narrower gap should not be confused with neither company explaining what occurred at all.

• Cursor published a security notice on October 29, 2026, with sections explaining what happened, its response, and remediation steps.
• Cursor said malicious extension versions 2.1.312 and 2.1.313 attempted to install a persistent SSH backdoor.
• On October 30, 2026, Anthropic staff member Felix Rieseberg publicly said an attacker used access to Cursor’s marketplace to publish a tampered extension that Anthropic neither built nor published.
• Microsoft independently reported that Anthropic confirmed its systems were not compromised and that the malicious packages were not distributed through Microsoft’s marketplace or Anthropic’s npm package.

1. techradar.com
2. axios.com
3. pcgamer.com
4. microsoft.com
5. arstechnica.com
6. csoonline.com
7. wired.com
8. securityweek.com

Following the October 29, 2026, supply chain incident involving a trojanized Claude Code extension on the Cursor VS Code Extension Marketplace, both Cursor and Anthropic publicly explained what occurred. Cursor published a formal security advisory stating that unauthorized, modified packages containing an SSH backdoor were live for roughly 11 hours and affected up to 5,000 users. Anthropic publicly clarified via public channels and security researchers that the incident was isolated to Cursor's marketplace and that Anthropic's own systems and official distribution channels were uncompromised.

• On October 29, 2026, Cursor issued a public security notice regarding tampered versions of the Claude Code extension (2.1.312 and 2.1.313) on its marketplace.
• Cursor publicly detailed the incident timeline, estimated that at most 5,000 users were impacted, and explained its remediation steps.
• Anthropic publicly clarified that its internal systems, developer laptops, and official distribution channels (such as npm and the Microsoft VS Code Marketplace) were not compromised.
• Both companies cooperated with external cybersecurity researchers and vendors, such as Microsoft Threat Intelligence, who published corroborating technical analyses.

1. microsoft.com
2. stepsecurity.io
3. securityweek.com
4. cursor.com
5. thehackernews.com
6. sophos.com

The claim that neither company publicly explained anything is contradicted by documented public statements: Cursor's marketplace alert and Anthropic's public denial both described what happened and what was and was not affected. The narrower point that the attackers' initial access route was not explained is supported by reporting, so the claim is false as worded but points at a real gap.

• Cursor's security alert said modified builds of Claude Code versions 2.1.312 and 2.1.313 were available in its marketplace for about 11 hours on October 29, 2026, affecting at most 5,000 users.
• Anthropic's Felix Rieseberg posted publicly on October 30, 2026 that the incident was not a breach of Anthropic systems or employee laptops and that official channels were unaffected.
• BleepingComputer reported on October 30, 2026 that Cursor had not explained how attackers distributed the compromised package under Anthropic's name.
• Independent researchers (OpenSourceMalware, StepSecurity) verified that builds on Open VSX and the Microsoft VS Code Marketplace did not contain the malicious code.
• The malicious loader added an SSH key labeled svc-telemetry, attempted a reverse SSH tunnel to an external server, and installed persistence mechanisms.

1. Signed by the Right Publisher: Trojanized Claude Code on Cursor’s Marketplace labs.cloudsecurityalliance.org
2. Anthropic 否认恶意 Claude Code 扩展涉及自身系统遭入侵：称攻击者借 Cursor 市场访问权发布篡改副本，官方渠道不受影响 hub-assets-cache.baai.ac.cn
3. Fake Claude Code extension in Cursor: How to find the backdoor expel.com
4. Malicious Claude Code extension on Cursor planted SSH backdoors bleepingcomputer.com
5. Claude Code Extension Trojanized on Cursor Marketplace with SSH Backdoor Add a tag - RH-ISAC rhisac.org
6. Cursor Confirms Anthropic Claude Code Extension Compromised bankinfosecurity.com

The claim is that neither Anthropic nor Cursor publicly explained what occurred during the Claude Code compromise incident. The evidence shows that both companies issued statements acknowledging the incident, confirming that Anthropic’s systems were not breached, and that the malicious extension was published via Cursor’s marketplace. However, neither company has provided a public explanation of how the attacker gained access to publish the extension under Anthropic’s name, nor have they detailed the specific attack vector or how the compromise occurred. This lack of public explanation is widely noted in cybersecurity reporting and analysis.

• Anthropic stated the incident was not a compromise of its systems or employee laptops, and that a malicious actor used access to Cursor’s marketplace to publish the tampered extension.
• Cursor removed the malicious extension, shut down its marketplace, rotated keys, and rebuilt the marketplace, but did not explain how the attacker gained access.
• The malicious extension was available for about 11 hours on October 29, 2026, and affected up to 5,000 users.
• Multiple sources confirm that neither company has provided a public explanation of the attack vector or how the extension was published under Anthropic’s identity.
• Anthropic and Cursor have not responded to requests for comment on the specifics of the compromise.

1. Anthropic: That Claude Code extension compromise ... theregister.com
2. A Supply Chain Attack Put Malicious Anthropic Claude Extensions on Thousands of Devices | WIRED wired.com
3. Official Claude Code Extension on Cursor Marketplace Trojanized with Persistent SSH Backdoor thehackernews.com
4. Investigating three incidents in our cybersecurity evaluations \ Anthropic anthropic.com
5. Trojanized Claude Code Extension Delivered Persistent SSH Backdoor to Developer Machines - StepSecurity stepsecurity.io
6. Anthropic hacked via Cursor to deliver remote access trojan to Claude developer laptops worldwide | by Kevin Beaumont | Oct, 2026 | DoublePulsar doublepulsar.com
7. Felix from Anthropic here. We’re working with Cursor on this incident, but it wa... | Hacker News news.ycombinator.com
8. Kevin Beaumont: "Anthropic Visual Studio Claude…" - Cyberplace cyberplace.social