CVE-2026-84364 Hono: Unbounded dot-notation nesting in `parseBody()` can cause memory exhaustion
An unauthenticated attacker can cause memory exhaustion and service downtime by sending crafted requests to endpoints using dot-notation parsing in Hono.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-84364?
CVE-2026-84364 is a medium-severity denial of service vulnerability in honojs hono, published on 1 Sep 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 4.13.5, when parseBody() expands dot-separated form field names into nested objects with dot-notation parsing enabled, it does not limit the nesting depth or the total number of intermediate objects created. Empty segments are preserved, so one deeply dotted field name can encode one nesting level per byte, while a large number of shallowly dotted fields can create the same amplification across a request. A request body within a normal size limit can therefore allocate an object graph far larger than the request after the body has already been accepted. An unauthenticated attacker who can reach an affected endpoint can send concurrent requests that exhaust the JavaScript heap, terminate the server process, and leave the service unavailable until restart. Dot-notation parsing is not enabled by default, and applications using the default behavior are not affected. This issue is fixed in version 4.13.5.
Weakness: CWE-400
Which versions are affected by CVE-2026-84364?
2 open source packages ship an affected version, including hono.
| Package | Affected | Fixed in |
|---|---|---|
hono npm | All versions | 4.13.5 |
hono npm | All versions | 4.13.5 |
How do I fix CVE-2026-84364?
Upgrade hono to 4.13.5 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-84364 being exploited?
There is no known exploitation of CVE-2026-84364 in the wild and no public exploit code.
Sources
Also known as CLEANSTART-2026-ZC19575, ECHO-b55e-2079-91a0, GHSA-g6gw-c38x-mqfc, MINI-5fjc-87qc-8j4f, MINI-6662-3f93-7xvg, MINI-7f2f-qhjv-9fv3 and 5 more.