GHSA-r4q5-vmmm-2653 — follow-redirects leaks Custom Authentication Headers to Cross-Domain Redirect Targets

Affected: npm: follow-redirects

## Summary

When an HTTP request follows a cross-domain redirect (301/302/307/308), `follow-redirects` only strips `authorization`, `proxy-authorization`, and `cookie` headers (matched by regex at index.js:469-476). Any custom authentication header (e.g., `X-API-Key`, `X-Auth-Token`, `Api-Key`, `Token`) is forwarded verbatim to the redirect target.

Since `follow-redirects` is the redirect-handling dependency for **axios** (105K+ stars), this vulnerability affects the entire axios ecosystem.

## Affected Code

`index.js`, lines 469-476:

```javascript if (redirectUrl.protocol !== currentUrlParts.protocol && redirectUrl.protocol !== "https:" || redirectUrl.host !== currentHost && !isSubdomain(redirectUrl.host, currentHost)) { removeMatchingHeaders(/^(?:(?:proxy-)?authorization|cookie)$/i, this._options.headers); } ```

The regex only matches `authorization`, `proxy-authorization`, and `cookie`. Custom headers like `X-API-Key` are not matched.

## Attack Scenario

1. App uses axios with custom auth header: `headers: { 'X-API-Key': 'sk-live-secret123' }` 2. Server returns `302 Location: https://evil.com/steal` 3. follow-redirects sends `X-API-Key: sk-live-secret123` to `evil.com` 4. Attacker captures the API key

## Impact

Any custom auth header set via axios leaks on cross-domain redirect. Extremely common pattern. Affects all axios users in Node.js.

## Suggested Fix

Add a `sensitiveHeaders` option that users can extend, or strip ALL non-standard headers on cross…

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GHSA-r4q5-vmmm-2653 — follow-redirects leaks Custom Authentication Headers to Cross-Domain Redirect Targets