Claude Code Leaks Data via Malicious Environment Configuration Before Trust Confirmation

Exploitation

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

CVSS 4.0

5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-21852: 27.50% estimated exploitation activity in the next 30 days; percentile 98.08 (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.

A vulnerability in Claude Code's project-load flow allowed malicious repositories to exfiltrate data including Anthropic API keys before users confirmed trust. If a user started Claude Code in an attacker-controller repository, and the repository included a settings file that set ANTHROPICBASEURL to an attacker-controlled endpoint, Claude Code would issue API requests before showing the trust prompt, including potentially leaking the user's API keys. Users on standard Claude Code auto-update have received this fix already. Users performing manual updates are advised to update to the latest version.

Published by the source

21 Jan 2026, 01:00 UTC

Last modified by the source

3 Feb 2026, 03:11 UTC

Source last checked

26 Oct 2026, 12:41 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jh7p-qr78-84p7

2. Revision 2 · amended · 24 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-jh7p-qr78-84p7

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# Patch Next advisory brief: CVE-2026-21852

Advisory: Claude Code Leaks Data via Malicious Environment Configuration Before Trust Confirmation
IDs: CVE-2026-21852, GHSA-jh7p-qr78-84p7
Record: https://patchnext.com/advisories/cve-2026-21852 (revision 3, source checked 26 Oct 2026, 12:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
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 2.0.65. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @anthropic-ai/claude-code: affected < 2.0.65; fixed in 2.0.65

## 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-jh7p-qr78-84p7 (OSV record GHSA-jh7p-qr78-84p7 lists affected ranges: npm @anthropic-ai/claude-code >=0 <2.0.65 (fixed))
- Verified: https://github.com/advisories/GHSA-jh7p-qr78-84p7 (GitHub-reviewed advisory GHSA-jh7p-qr78-84p7 lists affected ranges: npm @anthropic-ai/claude-code >=0 <2.0.65)

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