CVE-2026-39861: Claude Code Sandbox Escape Vulnerability

HIGH
Advisory Identifier: GHSA-vp62-r36r-9xqp
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CVSS 10.0
CWE-61 CWE-22
Published
Advisory Summary

CVE-2026-39861 is a HIGH (CVSS 10.0) sandbox escape vulnerability (CWE-61: UNIX Symbolic Link (Symlink) Following) affecting Claude Code libraries in the npm ecosystem. The issue involves sandbox escape via symlink following allows arbitrary file write outside workspace. Remediation is available by upgrading affected packages to version 2.1.64.

CVE-2026-39861 at a Glance

CVE Identifier CVE-2026-39861
GHSA Identifier GHSA-vp62-r36r-9xqp
Severity HIGH
CVSS v3.1 Base Score 10.0
CWE Classification CWE-61: UNIX Symbolic Link (Symlink) Following
Affected Product Claude Code
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 10.0

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Changed (S:C)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2026-39861

To remediate this vulnerability, upgrade all affected Claude Code dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

@anthropic-ai/claude-code fixed: 2.1.64 
npm install @anthropic-ai/claude-code@2.1.64
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls @anthropic-ai/claude-code

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-39861, inspect your project dependencies using npm:

npm ls @anthropic-ai/claude-code

Analyze the terminal output to locate any version of Claude Code in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.1.64), your application is affected.

Note: The npm ls @anthropic-ai/claude-code command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-61: UNIX Symbolic Link (Symlink) Following, where the product, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere. this could allow an attacker to cause the product to operate on unauthorized files. In Claude Code, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2026-39861 Affected Claude Code Versions

1 component(s)
Fixed Versions:
2.1.64
Product / Package Ecosystem Affected Versions Fixed Version
@anthropic-ai/claude-code
npm/@anthropic-ai/claude-code
npm
< 2.1.64
2.1.64

References

GitHub Advisory / Wiki ADVISORY
https://github.com/anthropics/claude-code/security/advisories/GHSA-vp62-r36r-9xqp
NVD — CVE-2026-39861 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-39861
Claude Code Source Repository REPOSITORY
https://github.com/anthropics/claude-code

Frequently Asked Questions

What is CVE-2026-39861?
CVE-2026-39861 is a security vulnerability in Claude Code involving Sandbox Escape via Symlink Following Allows Arbitrary File Write Outside Workspace under CWE-61: UNIX Symbolic Link (Symlink) Following.
Which Claude Code versions are affected?
Affected versions include releases prior to 2.1.64 across affected packages: @anthropic-ai/claude-code.
What version fixes CVE-2026-39861?
Upgrading to 2.1.64 (or the latest patched release for your respective branch) resolves the vulnerability.
Is @anthropic-ai/claude-code affected?
Yes, @anthropic-ai/claude-code is affected in releases prior to 2.1.64. Upgrade your dependency to 2.1.64 or later.
What is the CVSS score of CVE-2026-39861?
CVE-2026-39861 has a CVSS v3.1 base score of 10.0 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H.
What CWE is associated with CVE-2026-39861?
CVE-2026-39861 is classified under CWE-61: UNIX Symbolic Link (Symlink) Following (The product, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere. This could allow an attacker to cause the product to operate on unauthorized files.).
How can I check npm dependencies for CVE-2026-39861?
Run the dependency tree command: 'npm ls @anthropic-ai/claude-code'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vp62-r36r-9xqp",
  "modified" : "2026-04-27T16:34:21Z",
  "published" : "2026-04-21T18:51:21Z",
  "aliases" : [ "CVE-2026-39861" ],
  "summary" : "Claude Code: Sandbox Escape via Symlink Following Allows Arbitrary File Write Outside Workspace",
  "details" : "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.\n\nUsers on standard Claude Code auto-update have received this fix automatically. Users performing manual updates are advised to update to the latest version.\n\nClaude Code thanks hackerone.com/philts for reporting this issue.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@anthropic-ai/claude-code"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.1.64"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/anthropics/claude-code/security/advisories/GHSA-vp62-r36r-9xqp"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-39861"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/anthropics/claude-code"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22", "CWE-61" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-21T18:51:21Z",
    "nvd_published_at" : "2026-04-21T01:16:06Z"
  }
}