# CVE-2026-71849: Hono: Proxy Helper does not remove response headers listed in the `Connection` header

> The Hono framework's proxy helper fails to remove hop-by-hop headers, potentially disclosing internal metadata to clients.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Aug 2026
- **Updated:** 10 Aug 2026
- **Also known as:** CLEANSTART-2026-AV60851, ECHO-48a8-f364-cd95, GHSA-79qm-7rj5-m7r9, MINI-5x82-w7h7-45p8, MINI-6447-r75f-32fx, MINI-6mhc-j8j4-79q2, MINI-9cpg-qf2r-wcxr, MINI-f24c-hcc5-qwrf, MINI-gq3m-hr4f-9g8r, MINI-jwvj-gh43-cv73, MINI-ph9h-r76v-rx57, MINI-vrpm-gjhc-g2fv, MINI-whj5-58j2-qw49, MINI-xw5p-w23m-5hhm

## What is CVE-2026-71849?

CVE-2026-71849 is a low-severity vulnerability in honojs hono, published on 7 Aug 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. From 4.7.0 to 4.12.33, the Proxy Helper proxy() function in hono/proxy does not remove response headers named by the origin's Connection header. Per RFC 9110 Section 7.6.1, an intermediary must remove the header fields listed in a message's Connection header field before forwarding the message, in addition to the well known hop by hop headers, but the proxy() function only removed the well known hop by hop headers, including Connection itself, from origin responses. A client may therefore receive response headers that the origin intended only for its immediate peer, disclosing connection scoped or internal metadata contained in such headers, when an application proxies responses from an origin that declares additional, non standard headers as hop by hop via the Connection response header. This issue is fixed in version 4.12.34.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2026-71849?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hono` | npm | From 4.7.0 | 4.12.34 |
| `hono` | npm | From 4.7.0 | 4.12.34 |

## How do I fix CVE-2026-71849?

Upgrade hono to 4.12.34 or later.

## Is CVE-2026-71849 being exploited?

There is no known exploitation of CVE-2026-71849 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-71849 and fix it if it is affected.

What it is: CVE-2026-71849 is a low-severity vulnerability in honojs hono, published on 7 Aug 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-2026-71849 in the wild and no public exploit code.

Affected packages and fixed versions:
- hono (npm): affected from 4.7.0; fixed in 4.12.34
- hono (npm): affected from 4.7.0; fixed in 4.12.34

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-2026-71849/ (Markdown: https://insights.sbomify.com/CVE-2026-71849/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-71849
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-71849
- OSV: https://osv.dev/vulnerability/CVE-2026-71849

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-71849/
Summaries are generated and may contain mistakes; the official description above is the record.