A trojanized version of an extension carrying the identity of Anthropic's official Claude Code has reportedly been distributed with an SSH backdoor through Cursor's extension marketplace, affecting as many as 5,000 users, according to Cursor.
Supply-chain attack · Cursor extension marketplace
A trojanized Claude Code extension carried an SSH backdoor to as many as 5,000 users
A malicious build, v2.1.313, was pushed as an update under the identity of Anthropic's official Claude Code extension. The reporting does not yet establish how many affected users were actually compromised, or how the update was published.
5,000
Maximum users who may have installed or updated the affected build
v2.1.313
The malicious version distributed as an extension update
Not known
How many affected users were actually compromised
Scale of exposure
Each block = 500 users, drawn to scale against the reported maximum.
5,000
Up to affected users
Unknown
Confirmed compromised, not established
How the attack appears to flow
1 · Identity
Build presented as official Claude Code
→
2 · Update
Malicious v2.1.313 pushed to users
→
3 · Install
Users install or update the extension
→
4 · Access
SSH backdoor offers hidden remote access
The route used to publish the update under the legitimate identity is not explained in available reporting.
What is reported
A trojanized build, v2.1.313, is linked to the extension
It contains an SSH backdoor for remote access
Up to 5,000 users may be affected
What remains open
How many users were actually compromised
What an attacker did after gaining access
How the malicious update was published
Why it matters
Developer tools hold broad permissions, source code and credentials, which makes trusted update channels a high-value target.
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