CVE-2026-71849
LowCVSS 3.7Exploitation Probability (EPSS)
Low risk15th percentile - higher than 15% of all known CVEs
Summary
Hono is a web application framework supporting any JavaScript runtime. From 4.7.0 to 4.12.33, the proxy() function in hono/proxy does not remove response headers named by the origin's Connection header. Per RFC 9110, an intermediary must remove these headers before forwarding, but the function only removes standard hop-by-hop headers, potentially leading to disclosure of internal metadata.
Risk Assessment
Clients may receive response headers that the origin intended only for its immediate peer, potentially exposing connection-scoped or internal metadata.
Recommendation
Update Hono to version 4.12.34 or later, which contains the fix. If not possible, manually remove headers indicated by Connection in proxy responses.
Original NVD description (English source)
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.