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The vulnerability CVE-2025-66032 in Claude Code prior to version 1.0.93 arises from flawed parsing logic for shell commands involving the $IFS environment variable and short CLI flags. The tool’s read-only validation mechanism, designed to prevent unauthorized code execution, incorrectly processes these elements, allowing attackers to craft inputs that bypass security checks. Specifically, when $IFS is used in commands, it manipulates internal field separators to disguise malicious instructions as benign, evading pattern-based detection. Simultaneously, short CLI flags are not adequately sanitized, enabling additional evasion techniques. By combining these parsing errors, an attacker can inject payloads into the Claude Code context window—where untrusted content can be added—to trick the system into executing arbitrary shell commands. This exploitation leads to full code execution within the Claude Code environment, compromising the underlying system if the tool has necessary privileges. The issue is rooted in how command strings are tokenized and validated, failing to account for alternative whitespace characters and flag abbreviations commonly used in shell environments.
Platform: Claude Code
Version: Before 1.0.93
Vulnerability: Arbitrary code execution
Severity: Critical
Date: 2025-12-03
Prediction: Fixed in 1.0.93
What Undercode Say:
Analytics:
Example payload using $IFS to bypass space detection malicious_cmd="cat$IFS/etc/passwd" Exploiting short CLI flags for evasion payload="-f malicious_script.sh" Combined attack vector exploit="echo$IFS'pwned'$IFS&&-x$IFS/bin/bash"
How Exploit:
Craft input with $IFS replacing spaces and short flags to bypass read-only validation, injecting into Claude Code context for arbitrary command execution.
Protection from this CVE:
Update to version 1.0.93.
Impact:
Arbitrary code execution, system compromise.
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Sources:
Reported By: nvd.nist.gov
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