CVE-2025-66032: Anthropic Claude Code RCE Vulnerability

CVE-2025-66032 Overview

CVE-2025-66032 is a command injection vulnerability affecting Anthropic Claude Code, an agentic coding tool. Prior to version 1.0.93, errors in parsing shell commands related to $IFS (Internal Field Separator) and short CLI flags allowed attackers to bypass the Claude Code read-only validation mechanism and trigger arbitrary code execution. Reliably exploiting this vulnerability requires the ability to add untrusted content into a Claude Code context window.

Critical Impact

This vulnerability enables attackers to bypass security controls and execute arbitrary code on systems running vulnerable versions of Claude Code, potentially compromising developer workstations and sensitive codebases.

Affected Products

• Anthropic Claude Code versions prior to 1.0.93
• Claude Code Node.js package installations
• Development environments using vulnerable Claude Code CLI

Discovery Timeline

• 2025-12-03 - CVE-2025-66032 published to NVD
• 2025-12-05 - Last updated in NVD database

Technical Details for CVE-2025-66032

Vulnerability Analysis

This command injection vulnerability (CWE-77) stems from improper parsing of shell commands within Claude Code's read-only validation mechanism. The vulnerability specifically involves manipulation of the $IFS environment variable and short CLI flag handling, which are common attack vectors for bypassing shell command validation.

The $IFS variable in Unix-like shells defines how the shell interprets word boundaries. When improperly handled, attackers can manipulate this variable to alter how command arguments are parsed, effectively bypassing security filters that rely on string-based validation. Combined with short CLI flag manipulation, this parsing flaw allows crafted input to circumvent the read-only restrictions intended to prevent code modification and execution.

The attack requires user interaction in the form of adding untrusted content to a Claude Code context window, which could occur through various social engineering techniques or by manipulating files that Claude Code processes.

Root Cause

The root cause lies in insufficient input validation and improper shell command parsing within Claude Code's security boundary enforcement. The read-only validation logic failed to account for shell metacharacter manipulation via $IFS and edge cases in short CLI flag parsing, creating a gap between the intended security model and actual shell behavior.

Attack Vector

The attack vector is network-based and requires user interaction. An attacker must craft malicious content that, when introduced into a Claude Code context window, exploits the shell parsing errors to bypass read-only validation. This could be achieved through:

• Maliciously crafted code repositories that a user opens with Claude Code
• Manipulated files containing specially formatted content designed to trigger the parsing flaw
• Social engineering users into pasting malicious content into Claude Code sessions

The vulnerability leverages the difference between how Claude Code's validation logic interprets commands versus how the underlying shell executes them when $IFS manipulation and short flag formats are involved.

Detection Methods for CVE-2025-66032

Indicators of Compromise

• Unexpected shell commands executed from Claude Code processes
• Unusual $IFS variable modifications in shell environment logs
• Claude Code processes spawning unexpected child processes
• Anomalous file system modifications in directories accessed by Claude Code

Detection Strategies

• Monitor Claude Code process execution for unexpected command patterns
• Implement logging for shell command invocations from Claude Code
• Review application logs for malformed CLI flag sequences
• Deploy endpoint detection rules for $IFS manipulation attempts

Monitoring Recommendations

• Enable comprehensive logging for Claude Code sessions
• Monitor for process execution anomalies from Node.js-based applications
• Implement file integrity monitoring on critical development directories
• Review audit logs for unusual command execution patterns

How to Mitigate CVE-2025-66032

Immediate Actions Required

• Update Claude Code to version 1.0.93 or later immediately
• Review recent Claude Code sessions for suspicious activity
• Audit any projects that may have processed untrusted content
• Verify integrity of codebases accessed through Claude Code

Patch Information

Anthropic has addressed this vulnerability in Claude Code version 1.0.93. The fix corrects the shell command parsing logic to properly handle $IFS manipulation and short CLI flag edge cases. Users should update their Claude Code installation using the appropriate package manager.

For detailed information about the security fix, refer to the GitHub Security Advisory GHSA-xq4m-mc3c-vvg3.

Workarounds

• Avoid processing untrusted content through Claude Code until patched
• Restrict Claude Code usage to trusted, verified repositories only
• Run Claude Code in isolated environments with limited permissions
• Implement network segmentation for development environments using Claude Code

# Update Claude Code to patched version
npm update @anthropic/claude-code
# Verify installed version
claude-code --version
# Expected output: 1.0.93 or higher