Claude Code: Out-of-Band Data Exfiltration via Pre-Approved HuggingFace Domain in WebFetch

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-54316: 0.52% estimated exploitation activity in the next 30 days; percentile 44.24 (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.

Because the hostname huggingface.co was pre-approved as a bare hostname for the WebFetch tool, any path on that domain—including attacker-controlled model repositories—was auto-approved without a permission prompt or being subject to --allowedTools restrictions. An attacker able to inject untrusted content into a Claude Code context could direct it to issue WebFetch requests against attacker-controlled repository files (e.g. /resolve/main/config.json), which HuggingFace counts as downloads server-side, creating a covert out-of-band channel for encoding and exfiltrating data Claude can access such as files, environment variables, or command output. Reliably exploiting this required the ability to add untrusted content into a Claude Code context window. Users on standard Claude Code auto-update have received this fix already; users performing manual updates are advised to update to the latest version. Thank you to hackerone.com/novee for reporting this issue.

Published by the source

17 Jun 2026, 18:06 UTC

Last modified by the source

20 Jul 2026, 21:15 UTC

Source last checked

26 Oct 2026, 12:57 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-fg94-h982-f3mm

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-fg94-h982-f3mm

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# Patch Next advisory brief: CVE-2026-54316

Advisory: Claude Code: Out-of-Band Data Exfiltration via Pre-Approved HuggingFace Domain in WebFetch
IDs: CVE-2026-54316, GHSA-fg94-h982-f3mm
Record: https://patchnext.com/advisories/cve-2026-54316 (revision 3, source checked 26 Oct 2026, 12:57 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.0)
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 2.1.163. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @anthropic-ai/claude-code: affected >= 0.2.54, < 2.1.163; fixed in 2.1.163

## 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-fg94-h982-f3mm (OSV record GHSA-fg94-h982-f3mm lists affected ranges: npm @anthropic-ai/claude-code >=0.2.54 <2.1.163 (fixed))
- Verified: https://github.com/advisories/GHSA-fg94-h982-f3mm (GitHub-reviewed advisory GHSA-fg94-h982-f3mm lists affected ranges: npm @anthropic-ai/claude-code >=0.2.54 <2.1.163)

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