CVE-2026-39861

Claude Code's sandbox did not prevent sandboxed processes from creating symlinks pointing to locations outside the workspace. When Claude Code subsequently wrote to a path within such a symlink, its unsandboxed process followed the symlink and wrote to the target location outside the workspace without prompting the user for confirmation. This allowed a sandbox escape where neither the sandboxed command nor the unsandboxed app could independently write outside the workspace, but their combination could write to arbitrary locations, potentially leading to code execution outside the sandbox. Reliably exploiting this required the ability to add untrusted content into a Claude Code context window to trigger sandboxed code execution via prompt injection.

Users on standard Claude Code auto-update have received this fix automatically. Users performing manual updates are advised to update to the latest version.

Claude Code thanks hackerone.com/philts for reporting this issue.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-39861 has a CVSS score of 10.0 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.1.64); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-39861? CVE-2026-39861 is a high-severity path traversal vulnerability in @anthropic-ai/claude-code (npm), affecting versions < 2.1.64. It is fixed in 2.1.64. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-39861? CVE-2026-39861 has a CVSS score of 10.0 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of @anthropic-ai/claude-code are affected by CVE-2026-39861? @anthropic-ai/claude-code (npm) versions < 2.1.64 is affected.
4. Is there a fix for CVE-2026-39861? Yes. CVE-2026-39861 is fixed in 2.1.64. Upgrade to this version or later.
5. Is CVE-2026-39861 exploitable, and should I be worried? Whether CVE-2026-39861 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-39861 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-39861? Upgrade @anthropic-ai/claude-code to 2.1.64 or later.