CVE-2026-29087 is a high-severity (CVSS 7.5) CWE-863 vulnerability in @hono/node-server. A fix is available for @hono/node-server — see the affected versions and patch details below.
@hono/node-server: Authorization bypass for protected static paths via encoded slashes in Serve Static Middleware
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-2026-29087.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-29087 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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.
@hono/node-servernpmDescription
Summary
When using @hono/node-server's static file serving together with route-based middleware protections (e.g. protecting /admin/*), inconsistent URL decoding can allow protected static resources to be accessed without authorization.
In particular, paths containing encoded slashes (%2F) may be evaluated differently by routing/middleware matching versus static file path resolution, enabling a bypass where middleware does not run but the static file is still served.
Details
The routing layer and the node-server static handler normalize request paths differently. The router preserves %2F as a literal string when matching routes, while the static handler decodes %2F into / before resolving the filesystem path.
Example request:
/admin%2Fsecret.html
This may:
- fail to match middleware intended for
/admin/*, but - still be resolved by the static handler as
/admin/secret.htmlunder the configured static root.
This does not allow access outside the configured static root and is not a path traversal vulnerability.
Impact
An unauthenticated attacker could bypass route-based authorization protections for protected static resources by supplying paths containing encoded slashes.
Applications relying solely on route-based middleware to protect static subpaths under the same static root may have exposed those resources.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @hono/node-server | all versions | 1.19.10npm install @hono/node-server@1.19.10 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @hono/node-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @hono/node-server to 1.19.10 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-29087 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-29087 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-29087. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-29087 in your dependencies?
O3 Security finds CVE-2026-29087 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.