CVE-2026-29045 is a high-severity (CVSS 7.5) CWE-177 vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono: Arbitrary file access via serveStatic vulnerability
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- 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-2026-29045.
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
When using serveStatic together with route-based middleware protections (e.g. app.use('/admin/*', ...)), inconsistent URL decoding allowed protected static resources to be accessed without authorization.
The router used decodeURI, while serveStatic used decodeURIComponent. This mismatch allowed paths containing encoded slashes (%2F) to bypass middleware protections while still resolving to the intended filesystem path.
Details
The routing layer preserved %2F as a literal string, while serveStatic decoded it into / before resolving the file path.
Example:
Request: /admin%2Fsecret.html
- Router sees:
/admin%2Fsecret.html→ does not match/admin/* - Static handler resolves:
/admin/secret.html
As a result, static files under the configured static root could be served without triggering route-based protections.
This only affects applications that both:
- Protect subpaths using route-based middleware, and
- Serve files from the same static root using
serveStatic.
This does not allow access outside the static root and is not a path traversal vulnerability.
Impact
An unauthenticated attacker could bypass route-based authorization for protected static resources by supplying paths containing encoded slashes.
Applications relying solely on route-based middleware to protect static subpaths may have exposed those resources.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.12.4npm install hono@4.12.4 |
Affected Products
honohonoDetection & 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 4.12.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-29045 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
Frequently Asked Questions
Is CVE-2026-29045 in your dependencies?
Find it across npm, including transitive dependencies.