Claude Code: Sandbox Escape via Symlink Following Allows Arbitrary File Write Outside Workspace

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

7.7 · 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 · score source

EPSS

• CVE-2026-39861: 0.71% estimated exploitation activity in the next 30 days; percentile 53.61 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

21 Apr 2026, 18:51 UTC

Last modified by the source

5 May 2026, 16:11 UTC

Source last checked

26 Oct 2026, 12:51 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-vp62-r36r-9xqp

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-vp62-r36r-9xqp

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# Patch Next advisory brief: CVE-2026-39861

Advisory: Claude Code: Sandbox Escape via Symlink Following Allows Arbitrary File Write Outside Workspace
IDs: CVE-2026-39861, GHSA-vp62-r36r-9xqp
Record: https://patchnext.com/advisories/cve-2026-39861 (revision 3, source checked 26 Oct 2026, 12:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @anthropic-ai/claude-code 2.1.64. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @anthropic-ai/claude-code: affected < 2.1.64; fixed in 2.1.64

## Suggested inspection (read-only)
- `npm ls @anthropic-ai/claude-code --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @anthropic-ai/claude-code.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-vp62-r36r-9xqp (OSV record GHSA-vp62-r36r-9xqp lists affected ranges: npm @anthropic-ai/claude-code >=0 <2.1.64 (fixed))
- Verified: https://github.com/advisories/GHSA-vp62-r36r-9xqp (GitHub-reviewed advisory GHSA-vp62-r36r-9xqp lists affected ranges: npm @anthropic-ai/claude-code >=0 <2.1.64)

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