Claude Code's latest npm package accidentally included a 60MB source map, leaking the source code once again after a year.

According to 1M AI News monitoring, Fuzzland, a blockchain security company, intern researcher Chaofan Shou pointed out on X that the npm package of Claude Code, an AI programming tool under Anthropic, contains a complete source map file (cli.js.map, about 60MB), from which all TypeScript source code can be reconstructed. It was verified that this file appeared in the v2.1.88 released on March 30, while the previous version v2.1.87 (March 29) did not contain it. The package size also increased sharply from 17MB to 31MB (unpacked about 60MB) in the latest build, indicating an accidental introduction.

The reconstructed source map contains the full text of 1,906 Claude Code proprietary source files, covering implementation details such as internal API design, telemetry systems, encryption tools, inter-process communication protocols, etc. (excluding build configurations like package.json, which cannot be directly compiled and run). A source map is a debugging file used in JavaScript development to map compressed code back to the original source code and should not appear in a production release package.

When Claude Code was first released in February 2025, it was publicly discussed for including a source map. Subsequently, the file disappeared from the npm package, but the extraction of the source code did not stop. Currently, there are still multiple public repositories on GitHub that have organized the reconstructed source code, among which ghuntley/claude-code-source-code-deobfuscation has received nearly a thousand stars. The leaked code is the implementation code of the Claude Code CLI client, which does not involve model weights or user data, posing no direct security risk to ordinary users.