CVE-2026-29085 Hono: SSE Control Field Injection via CR/LF in writeSSE()
Attackers can inject arbitrary SSE fields via CR/LF characters in streamSSE() fields, potentially altering client-side event processing.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-29085?
CVE-2026-29085 is a medium-severity vulnerability in honojs hono, published on 4 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-74
Which versions are affected by CVE-2026-29085?
2 open source packages ship an affected version, including hono. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
hono npm | All versions | 4.12.4 |
hono npm | All versions | 4.12.4 |
Products include Hono Hono.
How do I fix CVE-2026-29085?
Upgrade hono to 4.12.4 or later.
Is CVE-2026-29085 being exploited?
There is no known exploitation of CVE-2026-29085 in the wild and no public exploit code.
Other vulnerabilities in honojs hono
- CVE-2026-27700 Hono is Vulnerable to Authentication Bypass by IP Spoofing in AWS Lambda ALB conninfo
- CVE-2026-22817 JWT Algorithm Confusion via Unsafe Default (HS256) in Hono JWT Middleware Allows Token Forgery and Auth Bypass
- CVE-2026-22818 JWT algorithm confusion in Hono JWK Auth Middleware when JWK lacks "alg" (untrusted header.alg fallback)
- CVE-2025-62610 Hono Improperly Authorizes JWT Audience Validation
- CVE-2026-29045 Hono: Arbitrary file access via serveStatic vulnerability
Sources
Also known as CLEANSTART-2026-DB28209, CLEANSTART-2026-FR80106, GHSA-p6xx-57qc-3wxr, MINI-5jx2-249r-qq79, MINI-64xr-h3mc-352j, MINI-6m73-74x5-h4h4 and 3 more.