fetch: Authorization headers not dropped when redirecting cross-origin

Exploitation

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

CVSS

7.5 · CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2025-21620: 0.52% estimated exploitation activity in the next 30 days; percentile 44.32 (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 you send a request with the Authorization header to one domain, and the response asks to redirect to a different domain, Deno'sfetch() redirect handling creates a follow-up redirect request that keeps the original Authorization header, leaking its content to that second domain. Details The right behavior would be to drop the Authorization header instead, in this scenario. The same is generally applied to Cookie and Proxy-Authorization headers, and is done for not only host changes, but also protocol/port changes. Generally referred to as "origin". The documentation states: Deno does not follow the same-origin policy, because the Deno user agent currently does not have the concept of origins, and it does not have a cookie jar. This means Deno does not need to protect against leaking authenticated data cross origin Reproduction

Published by the source

6 Jan 2025, 22:27 UTC

Last modified by the source

7 Jan 2025, 02:52 UTC

Source last checked

26 Oct 2026, 15:38 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-f27p-cmv8-xhm6

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# Patch Next advisory brief: CVE-2025-21620

Advisory: fetch: Authorization headers not dropped when redirecting cross-origin
IDs: CVE-2025-21620, GHSA-f27p-cmv8-xhm6
Record: https://patchnext.com/advisories/cve-2025-21620 (revision 1, source checked 26 Oct 2026, 15:38 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: deno_fetch 0.204.0; deno 2.1.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io deno_fetch: affected >= 0.0.1, < 0.204.0; fixed in 0.204.0
- crates.io deno: affected <= 1.46.3; >= 2.0.0, < 2.1.2; fixed in 2.1.2

## Suggested inspection (read-only)
- crates.io deno_fetch: check the installed version with your package manager.
- crates.io deno: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on deno_fetch, deno.
- 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://github.com/advisories/GHSA-f27p-cmv8-xhm6 (GitHub-reviewed advisory GHSA-f27p-cmv8-xhm6 lists affected ranges: crates.io deno_fetch >=0.0.1 =0 =2.0.0 <2.1.2)

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