Hono: Cookie helper does not sanitize sameSite and priority, allowing Set-Cookie injection

Exploitation

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

CVSS

4.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

EPSS

• CVE-2026-47675: 0.22% estimated exploitation activity in the next 30 days; percentile 12.09 (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 The serialize() function in hono/cookie validates domain and path options against characters that corrupt Set-Cookie header syntax (;, \r, \n), but does not apply the same validation to sameSite and priority. An application that passes user-controlled input into either option may produce a Set-Cookie response header containing attacker-chosen additional attributes. Details When constructing a Set-Cookie header value, serialize() appends the sameSite and priority option values directly into the output string after a presentation-only transformation (capitalizing the first character). Although the TypeScript type signature constrains these options to specific string literals, that constraint is not enforced at runtime; any string value, including one containing ; or line-feed characters, passes through unchanged. The validation guard that rejects ;, \r, and \n from domain and path is not applied to sameSite or priority. An application that passes a request-derived value to…

Published by the source

4 Jun 2026, 17:59 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:52 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-3hrh-pfw6-9m5x

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-3hrh-pfw6-9m5x

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# Patch Next advisory brief: CVE-2026-47675

Advisory: Hono: Cookie helper does not sanitize sameSite and priority, allowing Set-Cookie injection
IDs: CVE-2026-47675, GHSA-3hrh-pfw6-9m5x
Record: https://patchnext.com/advisories/cve-2026-47675 (revision 2, source checked 26 Oct 2026, 12:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: hono 4.12.21. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm hono: affected < 4.12.21; fixed in 4.12.21

## Suggested inspection (read-only)
- `npm ls hono --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 hono.
- 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-3hrh-pfw6-9m5x (OSV record GHSA-3hrh-pfw6-9m5x lists affected ranges: npm hono >=0 <4.12.21 (fixed))
- Verified: https://github.com/advisories/GHSA-3hrh-pfw6-9m5x (GitHub-reviewed advisory GHSA-3hrh-pfw6-9m5x lists affected ranges: npm hono >=0 <4.12.21)

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