UndiciApplication · Node.js
CVE-2026-9679
A fix is available.
Upgrade to 6.27.0 / 7.28.0 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable
No privileges
Zero-click
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 · uneditedImpact: undici's cookie parser in parseSetCookie percent-decodes cookie values via qsUnescape, turning encoded sequences like %0D%0A, %00, %3B, and %3D into their literal byte equivalents. RFC 6265 §5.4 does not specify any decoding and browsers do not decode either. Applications that parse a Set-Cookie header and then forward the parsed value into a response header (proxies, middleware, SSR frameworks) become vulnerable to HTTP response header injection: an attacker-controlled upstream can inject arbitrary Set-Cookie, Location, or Cache-Control headers into the application's downstream response, enabling session fixation, open redirect, or cache poisoning. Affected applications are those that use undici's cookie parsing (parseSetCookie, parseCookie, getSetCookies) and forward the parsed cookie value into a response header. This was introduced in undici 7.0.0 via PR #3789. Patches: Upgrade to undici v6.26.0, v7.28.0 or v8.5.0. Workarounds: If upgrade is not immediately possible, do not forward values returned by parseSetCookie/parseCookie/getSetCookies directly into response headers; sanitize the value first to strip or reject CR, LF, NUL, ;, and = bytes.
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 · low confidenceDeveloping — this CVE was published recently and its authoritative NVD entry is still being established, so we're holding a technical summary until the source data settles rather than publish something unreliable. Re-checking after 2026-07-30.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
UndiciApplication
Affected:
< 6.27.0>= 7.0.0, < 7.28.0>= 8.0.0, < 8.5.0CVSS 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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
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 · scoped
Upgrade available
Upgrade to 6.27.0 / 7.28.0 / 8.5.0 or later
Fixed in
6.27.07.28.08.5.0
Recommended fix
High confidence
undici v6.26.0, v7.28.0, or v8.5.0 (depending on your major version)
- Identify the currently installed undici version in your project by running `npm list undici` or checking package.json
- Determine which major version line you are on (v6, v7, or v8)
- Run `npm install [email protected]` if on the v6 line, `npm install [email protected]` if on v7, or `npm install [email protected]` if on v8
- Verify the upgrade was successful by running `npm list undici`
- Run your test suite to ensure the application functions correctly after the upgrade
- If tests pass, deploy the updated version
Caveat Minor release upgrades within the same major version typically have minimal breaking changes; however, review the undici changelog for any deprecation notices or behavioral changes between your current version and the target fixed version
Generated from the published advisory — verify against the referenced sources before acting.
We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600.
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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-2026-9679 in production — separate from our analysis above.
Know something about CVE-2026-9679?
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
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What belongs here
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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