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

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.21, 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. This vulnerability is fixed in 4.12.21.

Source published

28 May 2026 15:28:23 UTC

Source modified

28 May 2026 19:17:17 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.21, 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. This vulnerability is fixed in 4.12.21.

Source published

May 28, 2026, 3:28:23 PM (timezone not stated)

Source modified

May 28, 2026, 7:17:17 PM (timezone not stated)

Observed here

9 Nov 2026 12:02:51 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.21, 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. This vulnerability is fixed in 4.12.21.

Source published

28 May 2026 17:16:32 UTC

Source modified

14 Oct 2026 20:10:00 UTC

Observed here

25 Oct 2026 12:17:26 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 4.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

CVSS 3.1 · [email protected] · Primary · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

### 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 either option therefore provides an injection point into the header line. This issue arises when an application passes user-controlled input to the `sameSite` or `priority` option of `setCookie()` or `serialize()`. ### Impact An attacker who can control the `sameSite` or `priority` option value may inject additional attributes into a `Set-Cookie` response header. This may lead to: - Cookie attribute injection — overriding `Domain`, `Path`, `HttpOnly`, `Secure`, or `Max-Age` for the affected cookie - HTTP response header injection on runtimes that do not strictly validate header values, enabling a second attacker-controlled `Set-Cookie` header in the same response This issue affects applications that pass user-derived input into the `sameSite` or `priority` option of `hono/cookie` serialization functions.

Source published

4 Jun 2026 17:59:25 UTC

Source modified

10 Sep 2026 03:50:55 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Publisher rating · MODERATE