Anthropic Claude Code < 2.1.64 Sandbox Escape via Symlink Following (CVE-2026-39861)

high Nessus Plugin ID 310131

Synopsis

An application installed on the remote host is affected by a sandbox escape vulnerability.

Description

The version of Anthropic Claude Code installed on the remote host is prior to 2.1.64. It is, therefore, affected by a sandbox escape vulnerability.

- 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. (CVE-2026-39861)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Solution

Upgrade Anthropic Claude Code to version 2.1.64 or later.

Plugin Details

Severity: High

ID: 310131

File Name: anthropic_claude_code_CVE-2026-39861.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Misc.

Published: 4/24/2026

Updated: 4/24/2026

Supported Sensors: Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: High

Score: 8.1

CVSS v2

Risk Factor: Critical

Base Score: 10

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C

CVSS Score Source: CVE-2026-39861

CVSS v3

Risk Factor: Critical

Base Score: 10

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CVSS v4

Risk Factor: High

Base Score: 7.7

Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Vulnerability Information

CPE: cpe:/a:anthropic:claude_code

Required KB Items: installed_sw/Anthropic Claude Code

Patch Publication Date: 4/20/2026

Vulnerability Publication Date: 4/20/2026

Reference Information

CVE: CVE-2026-39861

IAVA: 2026-A-0375

Detections

Analytics