# A trojanized Claude Code extension reached thousands of users in 11 hours. I built a verify-before-install gate for agent extensions. > Source: > Published: 2026-11-04 13:31:57+00:00 # A trojanized Claude Code extension reached thousands of users in 11 hours. I built a verify-before-install gate for agent extensions. On 29/10/2026, a trojanized "Claude Code" extension sat on Cursor's marketplace for 11 hours and reached roughly 5,000 users. The payload appended an SSH key to ~/.ssh/authorized_keys, opened a reverse tunnel, and persisted on the machine. And the worst part: it did not even need typosquatting. It s erved wrong bytes under the right identifier (Anthropic.claude-code 2.1.312/2.1.313) — on one distribution path only. A verified publisher badge would have passed it. Identity is not safety. I built extverify — verify-before-install for agent extensions. One command, one verdict (ALLOW, DENY, or REVIEW) before the extension lands in your editor. Local, deterministic, zero runtime dependencies. $ extverify verify anthr0pic.claude-code@2.1.313 # recorded 29/10-shaped fixture DENY anthr0pic.claude-code@2.1.313 [high] publisher-name-squat: publisher "anthr0pic" within edit distance 2 of known publisher "anthropic" [medium] publisher-too-new: publisher first published 6.4 days ago (< 30d) [low] publisher-unverified: no verified domain badge [high] download-velocity-anomaly: 778 installs/day over 6.4d publisher age [medium] installs-no-ratings: 5000 installs with 0 ratings [medium] runs-on-startup: activationEvents includes "*" (code runs at every startup) [medium] bundled-binary: vsix ships executable: extension/bin/svc-telemetry [low] single-registry: version not found on Open VSX — cross-registry hash comparison unavailable Against a well-known extension, the verdict is different — and honestly so: $ extverify verify esbenp.prettier-vscode # live, real extension REVIEW esbenp.prettier-vscode@12.4.0 [medium] runs-on-startup: activationEvents includes "onStartupFinished" [medium] bundled-binary: vsix ships executable: extension/node_modules/prettier/bin/prettier.cjs [medium] cross-registry-hash-mismatch: version 12.4.0 has different sha256 on VS Marketplace vs Open VSX — registries disagree, verify out-of-band before installing REVIEW means "here are the signals, you decide." There is also extverify pin — trust a specific version once; version-repackaged fires DENY if the bytes change under that same version later. I cannot query the Cursor mirror. There is no public API for it. Against the exact 29/10 attack shape — correct identifier, wrong bytes, served on one path — listing-only checks produce REVIEW, not a confident DENY. A hard DENY needs the typosquat/velocity shape or your own local pin. If someone tells you they catch everything pre-install, ask which distribution paths they actually query. mcp-audit audits extensions post-install. That is a different trade-off: it can run deeper dynamic checks extverify never attempts, at the cost of letting the code touch your machine first. Socket is SaaS with real dependency-graph analysis — deeper than listing signals, but it requires an account and trusting a vendor with your manifest. extverify runs on your machine, no account, no network dependency at verdict time. Registry takedowns are post-hoc by design: the 29/10 payload shipped for 11 hours before anyone reacted. Pre-install gates and post-install audits are complements, not substitutes. git clone https://github.com/techdevfun/extverify && cd extverify npm install && npm run build extverify verify MIT, zero runtime dependencies. The checks are all in the README with their severities and rationale. If you find a listing shape it misjudges, open an issue with the listing — that is the fastest way to make the next incident shorter than 11 hours. ## Key Takeaways - •A verified publisher badge would have passed it. - •This story was reported by **Dev.to** , covering developments in the**dev** space. - •AI advancements continue to reshape industries — read the full article on Dev.to for complete coverage. 📖 Continue reading the full article: [Read Full Article on Dev.to →](https://dev.to/techdevfun/a-trojanized-claude-code-extension-reached-thousands-of-users-in-11-hours-i-built-a-4ja7)