CVE-2026-39410 Hono has a non-breaking space prefix bypass in cookie name handling in getCookie()
Attackers can bypass cookie prefix protections in Hono by exploiting parsing discrepancies, allowing them to override legitimate cookies.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-39410?
CVE-2026-39410 is a medium-severity vulnerability in honojs hono, published on 8 Apr 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 4.12.12, a discrepancy between browser cookie parsing and parse() handling allows cookie prefix protections to be bypassed. Cookie names that are treated as distinct by the browser may be normalized to the same key by parse(), allowing attacker-controlled cookies to override legitimate ones. This vulnerability is fixed in 4.12.12.
Weakness: CWE-20
Which versions are affected by CVE-2026-39410?
2 open source packages ship an affected version, including hono. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
hono npm | All versions | 4.12.12 |
hono npm | All versions | 4.12.12 |
Products include Hono Hono.
How do I fix CVE-2026-39410?
Upgrade hono to 4.12.12 or later.
Is CVE-2026-39410 being exploited?
There is no known exploitation of CVE-2026-39410 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-FR43043, CLEANSTART-2026-HB87291, GHSA-r5rp-j6wh-rvv4, MINI-653v-j5xq-fm5p, MINI-6q56-6rmp-227w, MINI-7m65-p6wq-w38q and 5 more.