CVE-2026-39861
10.0 · CRITICALOverview
CVE-2026-39861 is a critical-severity vulnerability affecting anthropic claude_code. It was published on April 21, 2026 and has a CVSS 3.1 base score of 10.0 (CRITICAL).
This vulnerability has a CVSS 3.1 base score of 10.0, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical Description
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.
Remediation
Check the references section for vendor advisories and patches from anthropic. Update claude_code to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| anthropic | claude_code | >= 0, < 2.1.64 | Affected |
Frequently Asked Questions
What is CVE-2026-39861?
CVE-2026-39861 is a critical-severity vulnerability affecting anthropic claude_code. It was published on April 21, 2026 and has a CVSS 3.1 base score of 10.0 (CRITICAL).
How severe is CVE-2026-39861?
This vulnerability has a CVSS 3.1 base score of 10.0, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2026-39861?
Check the references section for vendor advisories and patches from anthropic. Update claude_code to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-39861?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-39861 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
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