# 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.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Sep 2026
- **Updated:** 2 Sep 2026
- **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, MINI-83g6-r896-r83v, MINI-c632-cfw5-23gp, MINI-c7f6-6277-m4j8, MINI-h3ph-2m29-h6cm, MINI-h9xm-pq3g-35h5

## 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 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-84364?

2 open source packages ship an affected version, including hono.


| Package | Ecosystem | 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.

## Is CVE-2026-84364 being exploited?

There is no known exploitation of CVE-2026-84364 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-84364 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-84364 in the wild and no public exploit code.

Affected packages and fixed versions:
- hono (npm): affected all versions; fixed in 4.13.5
- hono (npm): affected all versions; fixed in 4.13.5

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-84364/ (Markdown: https://insights.sbomify.com/CVE-2026-84364/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-84364
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-84364
- OSV: https://osv.dev/vulnerability/CVE-2026-84364

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-84364/
Summaries are generated and may contain mistakes; the official description above is the record.