Claude Code is still vulnerable to an attack Anthropic has already fixed

The leak of Claude Code’s source is already having consequences for the tool’s security. Researchers have spotted a vulnerability documented in the code.

The vulnerability, revealed by AI security company Adversa, is that if Claude Code is presented with a command composed of more than 50 subcommands, then for subcommands after the 50th it will override compute-intensive security analysis that might otherwise have blocked some of them, and instead simply ask the user whether they want to go ahead. The user, assuming that the block rules are still in effect, may unthinkingly authorize the action.

Incredibly, the vulnerability is documented in the code, and Anthropic has already developed a fix for it, the tree-sitter parser, which is also in the code but not enabled in public builds that customers use, said Adversa.

Adversa outlined how attackers might exploit the vulnerability by distributing a legitimate-looking code repository containing a poisoned CLAUDE.md file. This would contain instructions for Claude Code to build the project, with a sequence of 50 or more legitimate-looking commands, followed by a command to, for example, exfiltrate the victim’s credentials. Armed with those credentials, the attackers could threaten a whole software supply chain.

This article first appeared on Infoworld.