CVE-2026-25723: Anthropic Claude Code Auth Bypass Flaw

CVE-2026-25723 Overview

Claude Code, an agentic coding tool developed by Anthropic, contains an improper input validation vulnerability in versions prior to 2.0.55. The vulnerability exists in the command validation logic, which failed to properly validate commands using piped sed operations with the echo command. This security flaw allows attackers to bypass file write restrictions and write to sensitive directories, including the .claude folder and paths outside the intended project scope.

Critical Impact

Attackers can bypass file write restrictions to modify sensitive configuration files and write to directories outside the project scope, potentially leading to arbitrary file write and system compromise.

Affected Products

• Anthropic Claude Code versions prior to 2.0.55
• Claude Code for Node.js environments

Discovery Timeline

• 2026-02-06 - CVE-2026-25723 published to NVD
• 2026-02-09 - Last updated in NVD database

Technical Details for CVE-2026-25723

Vulnerability Analysis

This vulnerability stems from improper input validation (CWE-20) in the command execution pipeline of Claude Code. The application's security controls designed to prevent file writes to restricted directories can be circumvented through specially crafted command chains that combine echo and piped sed operations.

The flaw is particularly significant because it undermines the sandboxing protections that Claude Code relies on to safely execute user-requested file operations. When the "accept edits" feature is enabled, the application should restrict file modifications to the designated project directory. However, the validation logic fails to account for command chaining scenarios involving sed with pipe redirection, allowing writes to escape the intended boundaries.

The attack requires network access and some user interaction (accepting the edit), but no special privileges are required to exploit this vulnerability once an attacker can influence the commands executed through Claude Code.

Root Cause

The root cause is inadequate input validation in the command sanitization layer. The validation logic did not properly parse and evaluate command pipelines involving shell redirection operators combined with text processing utilities like sed. This allowed attackers to construct command sequences that appeared benign to the validator but resulted in file writes to unauthorized locations when executed.

Attack Vector

The attack vector is network-based, requiring the attacker to have the ability to execute commands through Claude Code. Exploitation requires the "accept edits" feature to be enabled, which is the mechanism that allows Claude Code to make file modifications. An attacker could craft malicious input that, when processed by Claude Code, would execute a command pipeline that writes content to sensitive directories like .claude (containing configuration and credentials) or paths outside the project scope entirely.

The vulnerability could be triggered through:

• Malicious repository content that influences Claude Code's actions
• Prompt injection attacks that cause Claude Code to execute harmful commands
• Compromised external dependencies referenced in project files

Detection Methods for CVE-2026-25723

Indicators of Compromise

• Unexpected file modifications in the .claude directory or its configuration files
• New or modified files appearing outside the designated project directories
• Log entries showing command executions involving echo piped to sed with unusual file path targets
• Changes to Claude Code configuration that were not user-initiated

Detection Strategies

• Monitor file system activity for writes to .claude directories and parent directories above project roots
• Implement audit logging for all command executions through Claude Code, particularly those involving shell pipelines
• Review Claude Code execution logs for suspicious command patterns combining echo, sed, and file redirection
• Deploy file integrity monitoring on sensitive configuration directories

Monitoring Recommendations

• Enable verbose logging in Claude Code to capture full command execution details
• Set up alerts for any file write operations targeting paths outside the project directory
• Monitor for processes spawned by Claude Code that access sensitive system directories
• Regularly audit the .claude directory for unauthorized modifications

How to Mitigate CVE-2026-25723

Immediate Actions Required

• Upgrade Anthropic Claude Code to version 2.0.55 or later immediately
• Review file system for any unauthorized modifications, particularly in .claude directories
• Audit recent Claude Code sessions for suspicious command executions
• Temporarily disable the "accept edits" feature until the patch is applied if upgrade cannot be performed immediately

Patch Information

Anthropic has released version 2.0.55 of Claude Code which addresses this vulnerability. The patch improves the command validation logic to properly handle piped sed operations and other command chaining scenarios that could bypass file write restrictions.

For detailed information about the security fix, refer to the GitHub Security Advisory GHSA-mhg7-666j-cqg4.

Workarounds

• Disable the "accept edits" feature in Claude Code to prevent automatic file modifications until the patch can be applied
• Implement additional file system permissions to restrict write access to sensitive directories
• Run Claude Code in a containerized environment with strict volume mount restrictions
• Use file system sandboxing solutions to limit write access to only the intended project directory

# Upgrade Claude Code to patched version
npm update @anthropic/claude-code@2.0.55

# Verify the installed version
npm list @anthropic/claude-code