# CVE-2026-71849: Hono Proxy Helper information disclosure via hop-by-hop headers

Source: https://junglewise.ai/threats/cve-2026-71849-hono-proxy-helper-information-disclosure-via-hop-by-hop-headers  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-07. Updated: 2026-08-07  
License: CC BY 4.0 with a link back

CVE-2026-71849 · Severity: low · CVSS 3.7 · Published 2026-08-07

Hono is a web framework used to build applications and APIs. A vulnerability in its Proxy Helper component could allow sensitive internal information to be leaked to end-users. This occurs when the proxy fails to remove specific technical headers that were only intended for internal communication between servers, potentially exposing metadata about the internal network or infrastructure.

Technologies: [hono (npm)](https://junglewise.ai/threats/technologies/hono). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-71849 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-71849 being exploited in the wild.

**How severe is CVE-2026-71849?** Low severity, with a CVSS score of 3.7, published 7 August 2026.

**Which products and versions are affected?** hono (npm) >= 4.7.0, < 4.12.34, SEMVER:introduced=4.7.0,fixed=4.12.34.

**Is there a fix for CVE-2026-71849?** Yes. hono (npm): upgrade to 4.12.34 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-71849 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-71849?** Check whether you run hono (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- hono (npm): upgrade to 4.12.34 or later

  ```sh
  npm install hono@4.12.34
  ```


## Technical details

The Hono Proxy Helper (`hono/proxy`) violates RFC 9110 Section 7.6.1 by failing to remove headers designated as connection-scoped in the origin's `Connection` header field. While the `proxy()` function correctly removes standard hop-by-hop headers, it does not parse the `Connection` header to identify and strip additional non-standard headers declared by the origin. An attacker could potentially observe sensitive internal metadata or connection-specific information that was intended only for the intermediary proxy. This issue is specific to applications proxying origins that utilize custom hop-by-hop headers. The vulnerability is addressed in version 4.12.34.

## Affected products

- honojs hono >= 4.7.0, < 4.12.34

## Identifiers

- CVE-2026-71849
- GHSA-79qm-7rj5-m7r9

## Timeline

- 2026-08-03: patched: Fixed in version 4.12.34
- 2026-08-07: advisory: GitHub Advisory GHSA-79qm-7rj5-m7r9 published

## References

- [https://api.github.com/users/morgan-coded](https://api.github.com/users/morgan-coded)
- [https://github.com/morgan-coded](https://github.com/morgan-coded)
- [https://api.github.com/users/morgan-coded/gists%7B/gist_id%7D](https://api.github.com/users/morgan-coded/gists%7B/gist_id%7D)
- [https://api.github.com/users/morgan-coded/repos](https://api.github.com/users/morgan-coded/repos)
- [https://avatars.githubusercontent.com/u/256248948?v=4](https://avatars.githubusercontent.com/u/256248948?v=4)
- [https://api.github.com/users/morgan-coded/events%7B/privacy%7D](https://api.github.com/users/morgan-coded/events%7B/privacy%7D)

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