honojs Hono up to 4.12.33 Proxy Helper proxy information disclosure

Summaryinfo

A vulnerability described as problematic has been identified in honojs Hono up to 4.12.33. This affects the function proxy of the component Proxy Helper. Executing a manipulation can lead to information disclosure. This vulnerability is registered as CVE-2026-71849. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in honojs Hono up to 4.12.33. It has been declared as problematic. This vulnerability affects the function proxy of the component Proxy Helper. The manipulation with an unknown input leads to a information disclosure vulnerability. The CWE definition for the vulnerability is CWE-200. The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. As an impact it is known to affect confidentiality. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability was named CVE-2026-71849 since 08/07/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1592 by the MITRE ATT&CK project.

Upgrading to version 4.12.34 eliminates this vulnerability.

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Productinfo

Vendor

• honojs

Name

• Hono

Version

• 4.12.0
• 4.12.1
• 4.12.2
• 4.12.3
• 4.12.4
• 4.12.5
• 4.12.6
• 4.12.7
• 4.12.8
• 4.12.9
• 4.12.10
• 4.12.11
• 4.12.12
• 4.12.13
• 4.12.14
• 4.12.15
• 4.12.16
• 4.12.17
• 4.12.18
• 4.12.19
• 4.12.20
• 4.12.21
• 4.12.22
• 4.12.23
• 4.12.24
• 4.12.25
• 4.12.26
• 4.12.27
• 4.12.28
• 4.12.29
• 4.12.30
• 4.12.31
• 4.12.32
• 4.12.33

Website

• Product: https://github.com/honojs/hono/

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