Malicious Claude Code extensions found in Cursor marketplace
Your AI coding assistant just became a supply chain attack vector. An incident involving malicious versions of the Claude Code extension in the Cursor marketplace is a concrete reminder that the tools you trust most are exactly what attackers target.
What Happened
According to a report by cybrNK on OSINT Team, bad actors published fake Claude Code extensions to the Cursor marketplace. The extensions were designed to look like legitimate tooling but carried a payload: an SSH backdoor installed on the developer’s machine.
The featured meme from the incident cluster sums it up plainly: Claude extension installs SSH backdoor. That is not a hypothetical attack scenario. That is what happened to developers who installed the wrong extension.
Why This Attack Works
Developer tools occupy a privileged position on any machine. They run with elevated permissions, touch source code, access environment variables, and often have network access baked in. A malicious extension in a coding assistant marketplace does not need to exploit a zero day. It just needs to be installed.
Extension marketplaces in AI coding tools are relatively new and have less mature vetting processes than, say, the Chrome Web Store or npm. Attackers know this.
What to Do Right Now
- Audit every extension installed in Cursor, VS Code, or any AI coding assistant you use.
- Verify the publisher of each extension matches the official developer before trusting it.
- Treat any extension requesting unusual permissions (network, file system, shell access) as suspicious until verified.
- Check your
~/.ssh/authorized_keysand~/.ssh/configfor entries you did not add.
Supply chain attacks through developer tooling are not going away. As AI coding assistants grow in adoption, their extension ecosystems will attract more of this kind of targeting. The extension you installed in five seconds can cost you far more than five seconds to remediate.
I’m founder of BizStack at Cagri Sarigoz LLC and a passionate advocate for entrepreneurs.
With over 14 years in tech, marketing, and AI, including my role as Head of SEO at CitizenShipper and co-founder of TaleBot at Intale AI, I’m dedicated to sharing genuine, useful product insights and tips.
At BizStack, I aim to cut through the digital noise to provide clear, actionable advice.
And more than all else, I’m a father to a (always) little girl and a husband.
Contact me at [email protected] for assistance.
