# Anthropic's Claude extension backdoored for 12 hours

> A malicious version of Anthropic's VS Code extension on Cursor threatened up to 5,000 developers' machines before being removed.
- Title: Anthropic's Claude extension backdoored for 12 hours
- Summary: A malicious version of Anthropic's VS Code extension on Cursor threatened up to 5,000 developers' machines before being removed. Attackers compromised…
- Keywords: anthropic, claude, cursor, vs code, security breach, malware, supply chain attack, developers, technology, science, Anthropic's, extension
- Source: Ars Technica — https://arstechnica.com/security/2026/10/anthropic-vs-code-extension-on-cursor-backdoored-for-nearly-12-hours
- Published: 2026-10-30T21:09:54+00:00
- Read time: 1 min
- Topics: anthropic, claude, cursor, vs code, security breach, malware, supply chain attack, developers, technology, science
## Anthropic extension compromised
An official Anthropic Claude extension for VS Code on Cursor was backdoored, affecting at most five thousand developers. The malicious version was version two point one point three one three.
## How attackers gained access
The malicious version was posted to Anthropic's official account on Cursor, replacing version two point one point three one two.Extensions auto-update by default in Cursor.Neither Cursor nor Anthropic has explained how attackers gained control.

> It was a supply-chain compromise where the attacker gained access to the official distribution channel.
## What the backdoor did
The malicious extension attempted to install a persistent SSH backdoor using an attacker-controlled SSH key. It enabled the local SSH service and opened a reverse SSH tunnel. The code worked on Windows, macOS, and Linux.
## Data the backdoor collected
The backdoor collected hostname, username, OS, architecture, home directory path, environment variable names, working directories, configured Git email, and public IP. It attempted to add an attacker-controlled SSH key to authorized_keys.
## Why variable names mattered
Phorion said theft of variable names allowed the operator to quickly take inventory of cloud credentials and API tokens stored on compromised devices. This likely helped prioritize which machines to target in follow-up attacks.
## Response and removal
Cursor personnel worked with the cloud provider to block infected devices from reaching the reverse shell server.
## Timeline and unanswered questions
Anyone who installed or updated the extension between five twenty-seven am ET and four thirty-five pm on Thursday should consider themselves affected.
## Key takeaway

Attackers compromised Anthropic's official VS Code extension on Cursor, affecting up to 5,000 developers before the malicious version was replaced within hours.