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Claude CodeApplication · Anthropic

CVE-2026-39861

CRITICAL · 10.0 CVSS v3.1 Published 2026-04-21
Fix available
A fix is available. Upgrade to 2.1.64 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Claude Code is an agentic coding tool. Prior to version 2.1.64, 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 version 2.1.64 or later.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Claude Code versions before 2.1.64 had a sandbox escape vulnerability where sandboxed processes could create symlinks pointing outside the workspace. When the unsandboxed Claude Code process subsequently wrote to paths within these symlinks, it would follow them and write to arbitrary locations outside the workspace without user confirmation, enabling code execution outside the sandbox.

MitigationUpdate Claude Code to version 2.1.64 or later. Users on standard auto-update have received the fix automatically; manual update users must apply the update explicitly.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Claude CodeApplication
Affected:< 2.1.64

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Verify Claude Code installation
    Check if Claude Code CLI is installed by running 'claude --version' or 'claude -v' in the terminal
    Affected if Claude Code is not installed - not affected; if installed, proceed to version check
  2. Determine installed Claude Code version
    Run 'claude --version' and note the version number displayed (format typically shows like 'Claude Code 2.1.x')
    Affected if Unable to determine version - manual review required
  3. Compare version against affected range
    Compare the installed version number to 2.1.64 - versions before 2.1.64 are affected (e.g., 2.1.63, 2.1.60, etc.)
    Affected if Version is less than 2.1.64 (e.g., 2.1.63 or earlier) - environment is affected by this CVE
  4. Check if sandbox feature is used
    Determine if Claude Code sandbox mode is enabled - review Claude Code configuration files or check if sandboxed tool execution is in use (check for sandbox-related flags or settings in Claude Code config)
    Affected if Sandbox mode is not used - the specific exploitation path may not apply, but the vulnerable binary still exists
  5. Verify patch applied via update mechanism
    Run 'claude --version' again to confirm the current version after any updates, or check the application bundle/install location for version metadata
    Affected if Version remains below 2.1.64 after checking - vulnerable and requires update

A system is affected if Claude Code is installed with a version lower than 2.1.64 and the sandbox feature is in use, allowing symlink-based escape to write outside the workspace.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.1.64 or later
Fixed in 2.1.64
Interim mitigation

Update Claude Code to version 2.1.64 or later. Users on standard auto-update have received the fix automatically; manual update users must apply the update explicitly.

Recommended fix High confidence

2.1.64

  1. Check current Claude Code version by running 'claude --version' in terminal
  2. Update Claude Code to version 2.1.64 or later
  3. For auto-update users: ensure auto-update is enabled or run the update command for your installation method
  4. For manual users: download and install Claude Code 2.1.64 from the official Anthropic repository
  5. Verify the installed version is 2.1.64 or higher using 'claude --version'

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Claude Code Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing0.5 h
  • Review / QA0.5 h
3.0 hours of engineering $750
Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-39861 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data