CVE-2025-21620
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedDeno is a JavaScript, TypeScript, and WebAssembly runtime with secure defaults. 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. This vulnerability is fixed in 2.1.2.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceDeno's fetch() implementation improperly preserves the Authorization header during cross-domain redirects. When a request with authentication credentials to domain A receives a redirect response to domain B, the follow-up request to domain B automatically includes the original Authorization header, leaking sensitive credentials to what could be an untrusted third-party domain.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check your Deno versionRun 'deno --version' in your terminal to see the installed Deno versionAffected if The version is below 2.1.2 (the fixed release)
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Identify fetch calls with Authorization headersSearch your codebase for fetch() calls that include an 'Authorization' header in the headers object or as part of request optionsAffected if Your code uses fetch with Authorization headers and may encounter cross-domain redirects
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Review redirect-prone API endpointsAudit your code to identify fetch requests to domains that are known to return 3xx redirect responses, especially to third-party domainsAffected if Your application makes fetch requests to endpoints that may redirect to different domains
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Test redirect behaviorIf possible, make a test fetch request with an Authorization header to a URL that returns a redirect to a different domain and inspect whether the header is sent to the final destinationAffected if The Authorization header is automatically forwarded to the redirect target domain (this confirms the vulnerability)
You are affected if you use Deno below version 2.1.2 and your code uses fetch() with Authorization headers that may encounter cross-domain redirects.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade Deno to version 2.1.2 or later. As a temporary workaround, avoid sending Authorization headers to endpoints that may redirect, or manually handle redirects by making a new request without sensitive headers to the final destination.
2.1.2
- Upgrade Deno to version 2.1.2 or later to resolve the Authorization header leak vulnerability during cross-domain redirects.
- Verify the upgrade by checking the Deno version with `deno --version` command.
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2025-21620 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-21620 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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