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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-71849?
2 open source packages ship an affected version, including hono.
| Package | 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.
Sources
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 and 8 more.