CVE-2026-25725 in claude-code
Summary
by MITRE • 02/06/2026
Claude Code is an agentic coding tool. Prior to version 2.1.2, Claude Code's bubblewrap sandboxing mechanism failed to properly protect the .claude/settings.json configuration file when it did not exist at startup. While the parent directory was mounted as writable and .claude/settings.local.json was explicitly protected with read-only constraints, settings.json was not protected if it was missing. This allowed malicious code running inside the sandbox to create this file and inject persistent hooks (such as SessionStart commands) that would execute with host privileges when Claude Code was restarted. This issue has been patched in version 2.1.2.
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Analysis
by VulDB Data Team • 04/11/2026
The vulnerability identified as CVE-2026-25725 affects Claude Code, an agentic coding tool designed to provide secure development environments through sandboxing mechanisms. This security flaw represents a critical oversight in the sandboxing architecture that undermines the fundamental security assumptions of the application's isolation model. The vulnerability specifically targets the configuration file handling mechanism within the sandbox environment, creating a persistent backdoor opportunity that could be exploited by malicious actors.
The technical flaw stems from an incomplete implementation of the bubblewrap sandboxing system used by Claude Code. While the developers correctly identified that the parent directory containing configuration files should be mounted as writable to allow legitimate operations, they failed to apply consistent protection mechanisms to all configuration files within that directory. The .claude/settings.local.json file was properly configured with read-only constraints, but the primary settings.json file was not subjected to the same protection measures when it did not exist at startup. This discrepancy created a window of opportunity where malicious code could create the settings.json file and inject persistent hooks that would execute with elevated host privileges upon application restart.
The operational impact of this vulnerability is particularly severe as it enables persistent code execution with host-level privileges. When the sandboxed malicious code creates the settings.json file, it can inject SessionStart commands or similar persistent hooks that will automatically execute whenever Claude Code is restarted. This creates a stealthy backdoor that remains active across application sessions and could potentially allow attackers to maintain long-term access to the host system. The vulnerability essentially transforms a sandboxed execution environment into a persistent privilege escalation vector, undermining the core security principle that sandboxed code should not be able to affect the host system's operational state.
This vulnerability aligns with CWE-276, which addresses improper privileges, and represents a classic case of insufficient privilege separation in sandboxed environments. The issue also maps to ATT&CK technique T1059.001, which involves command and script interpreters, as attackers could leverage the injected hooks to execute arbitrary commands with host privileges. Additionally, the vulnerability demonstrates characteristics of T1547.001, which covers registry run keys and startup folder, as the persistent hooks would execute automatically during application startup. The patch implemented in version 2.1.2 addresses this by ensuring all configuration files within the .claude directory receive consistent protection regardless of their existence state at startup. Organizations should immediately update to version 2.1.2 or later to remediate this vulnerability, while also implementing monitoring for unauthorized configuration file modifications in affected environments.