Vulnerability · Published Mar 4, 2026 · Assigned by GitHub_M

CVE-2026-29085Hono: SSE Control Field Injection via CR/LF in writeSSE()

Medium 6.5

In plain English

A medium-severity injection in hono from honojs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 21% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.5Medium

Exploit odds (30 days)0.3%top 79.3% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to version 4.12.4, when using streamSSE() in Streaming Helper, the event, id, and retry fields were not validated for carriage return (\r) or newline (\n) characters. Because the SSE protocol uses line breaks as field delimiters, this could allow injection of additional SSE fields within the same event frame if untrusted input was passed into these fields. This issue has been patched in version 4.12.4.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	hono	4.12.4	GHSA-p6xx-57qc-3wxr

Affected products (as reported)

Vendor	Product	Versions
honojs	hono	< 4.12.4

Weakness: CWE-74 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

References

https://github.com/honojs/hono/security/advisories/GHSA-p6xx-57qc-3wxr x_refsource_CONFIRM
https://github.com/honojs/hono/commit/f4123ed9ea3c7c52380cc99a079a4d773838846e x_refsource_MISC