UNIX symbolic link following in Claude Code - CVE-2026-39861
Published: April 30, 2026
Vulnerability identifier: #VU128511
CSH Severity: High
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: CVE-2026-39861
CWE-ID: CWE-61
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Anthropic
Affected software:
Claude Code
Claude Code
Detailed vulnerability description
The vulnerability allows a remote attacker to write arbitrary files outside the workspace.
The vulnerability exists due to symlink following in the sandbox file write handling when writing to a path within an attacker-created symlink. A remote attacker can create a symlink pointing outside the workspace and cause Claude Code to write through it to write arbitrary files outside the workspace.
Reliable exploitation requires the ability to add untrusted content into a Claude Code context window to trigger sandboxed code execution via prompt injection.
How to mitigate CVE-2026-39861
Install security update from vendor's website.