follow-redirects leaks Custom Authentication Headers to Cross-Domain Redirect Targets

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-40895: 0.49% estimated exploitation activity in the next 30 days; percentile 41.92 (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.

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…

Published by the source

14 Apr 2026, 01:11 UTC

Last modified by the source

2 Nov 2026, 23:30 UTC

Source last checked

3 Nov 2026, 06:00 UTC

1. Revision 5 · amended · 3 Nov 2026

   Amended from osv record GHSA-r4q5-vmmm-2653

2. Revision 4 · amended · 3 Nov 2026

   Amended from ghsa record GHSA-r4q5-vmmm-2653

3. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-r4q5-vmmm-2653

4. Revision 2 · amended · 25 Oct 2026

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

5. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-r4q5-vmmm-2653

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# Patch Next advisory brief: CVE-2026-40895

Advisory: follow-redirects leaks Custom Authentication Headers to Cross-Domain Redirect Targets
IDs: CVE-2026-40895, GHSA-r4q5-vmmm-2653
Record: https://patchnext.com/advisories/cve-2026-40895 (revision 5, source checked 3 Nov 2026, 06:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: follow-redirects 1.16.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm follow-redirects: affected < 1.16.0; fixed in 1.16.0

## Suggested inspection (read-only)
- `npm ls follow-redirects --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 follow-redirects.
- 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-r4q5-vmmm-2653 (OSV record GHSA-r4q5-vmmm-2653 lists affected ranges: npm follow-redirects >=0 <1.16.0 (fixed))
- Verified: https://github.com/advisories/GHSA-r4q5-vmmm-2653 (GitHub-reviewed advisory GHSA-r4q5-vmmm-2653 lists affected ranges: npm follow-redirects >=0 <=1.15.11)

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