CVE-2026-71849 is a low-severity (CVSS 3.7) Information Exposure vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono: Proxy Helper does not remove response headers listed in the `Connection` header
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-71849.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
hononpmDescription
Summary
The Proxy Helper (hono/proxy) does not remove response headers named by the origin's Connection header. Headers that the origin marked as connection-scoped are therefore forwarded to clients.
Details
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. The proxy() function removed the well-known hop-by-hop headers (including Connection itself) from origin responses, but did not remove the headers that the response's Connection header field designated as connection-scoped.
This issue arises when an application proxies responses from an origin that declares additional, non-standard headers as hop-by-hop via the Connection response header.
Impact
A client may receive response headers that the origin intended only for its immediate peer. This may lead to:
- Disclosure of connection-scoped or internal metadata contained in such headers
This issue affects applications that use the Proxy Helper (hono/proxy) to forward responses from origins that list custom header names in their Connection response header. Applications whose origins only use the standard hop-by-hop headers are not affected.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | ≥ 4.7.0&&< 4.12.34 | 4.12.34npm install hono@4.12.34 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hono, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hono to 4.12.34 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-71849 is resolved across your whole dependency graph.
Workarounds
Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.
Frequently Asked Questions
Is CVE-2026-71849 in your dependencies?
Find it across npm, including transitive dependencies.