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-domain redirect.

Disclosure

Source code review, manually verified. Found 2026-03-20.

A flaw was found in follow-redirects when fetching a remote URL with a cookie when it gets to the Location response header. This flaw allows an attacker to hijack the account as the cookie is leaked.

A flaw was found in the follow-redirects package. This flaw allows the exposure of sensitive information to an unauthorized actor due to the usage of insecure HTTP protocol. This issue happens with an Authorization header leak from the same hostname, https-http, and requires a Man-in-the-Middle (MITM) attack.

follow-redirects is an open source, drop-in replacement for Node's http and https modules that automatically follows redirects. In affected versions follow-redirects only clears authorization header during cross-domain redirect, but keep the proxy-authentication header which contains credentials too. This vulnerability may lead to credentials leak, but has been addressed in version 1.15.6. Users are advised to upgrade. There are no known workarounds for this vulnerability.