CVE-2026-39861

OVERVIEW CVE-2026-39861 is a sandbox escape vulnerability in Claude Code, an agentic coding tool, affecting versions prior to 2.1.64. The flaw stems from the sandbox's failure to prevent sandboxed processes from creating symbolic links that point outside the designated workspace. When the unsandboxed application subsequently writes to a path containing such a symlink, it follows the link and writes to arbitrary locations outside the workspace without user confirmation, enabling unauthorized file modifications. SEVERITY This vulnerability requires a local attack vector involving prompt injection to add untrusted content into a Claude Code context window, making exploitation moderately complex. While neither the sandboxed process nor the unsandboxed application could independently write outside the workspace, their combination enables this capability. The potential impact is severe, as successful exploitation could lead to arbitrary code execution outside the sandbox environment. The FAUCET Risk Score of 48.0/100 reflects moderate concern, though the EPSS score of 0.00104 indicates relatively low prevalence compared to other CVEs. EXPLOITATION STATUS There is no evidence of active exploitation in the wild, and the vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog. No public exploit code has been reported. Users on automatic updates have received patches transparently, and manual update users are advised to upgrade to version 2.1.64 or later to remediate the risk.