NVD / CVE Program· CNA GitHub_M

CVE-2026-84365: Hono: Incomplete fix for CVE-2026-39408: `toSSG()` still writes files outside the output directory

MediumCVSS 6.5 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 26/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.43% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. No special conditions are required; it is repeatable.
Fixed version: honojs hono 4.13.5.

Low priority for now. Upgrade to honojs hono 4.13.5 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Hono is a Web application framework that provides support for any JavaScript runtime. From 4.12.12 until 4.13.5, the fix released for CVE-2026-39408 does not cover every traversal sequence, and toSSG() can still write files outside the configured output directory when a route parameter contains consecutive parent-directory segments. Static site generation builds each output path from the route path and values supplied through ssgParams, then verifies that the result stays inside the output directory using the same normalization routine that built the path. That routine does not fully collapse runs of consecutive parent-directory segments, allowing a path that the check accepts to resolve outside the output directory, and the check also treats output directories that differ in how they are rooted as equivalent. This arises when an application generates a static site from route parameter values it does not fully control, such as slugs from a CMS, API, or user submission. An untrusted ssgParams value can create or overwrite files elsewhere in the build environment and alter generated artifacts or deployment output. The vulnerability affects build-time static site generation only; request-time routing and applications with entirely developer-controlled ssgParams values are not affected. This issue is fixed in version 4.13.5.

Published: Sep 1, 2026
Updated: Sep 9, 2026
EPSS: 0.4% · 38th percentile
CWE: CWE-22

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 26 / 40 · 6.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.4%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 6.5; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

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Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

honojs hono
- < 4.13.5affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
npm	hono	before 4.13.5	4.13.5

Same product

honojs: all records

Other highest-scoring records for the same primary product.

CVE-2026-54290Hono: CORS Middleware reflects any Origin with credentials when `origin` defaults to the wildcard
28Monitor
CVE-2026-109955Hono 4.12.4 before 4.13.11 Middleware Bypass via serveStatic Double Decoding
27Monitor
CVE-2026-54288Hono: Body Limit Middleware can be bypassed on AWS Lambda by understating `Content-Length`
26Monitor

Published before and after this one in the same product

← EarlierCVE-2026-84363Sep 1, 2026 · Hono: Query parser reads parameters after the URL fragment, causing cache-key and proxy interpretation differentials
23Monitor
← EarlierCVE-2026-84364Sep 1, 2026 · Hono: Unbounded dot-notation nesting in `parseBody()` can cause memory exhaustion
21Monitor
Later →CVE-2026-93981Sep 19, 2026 · hono/jsx before 4.13.7 Cross-Site Scripting via Unescaped Strings
9Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
honojs hono	4.13.5 · description	Vendor (CNA)
npm:hono	4.13.5	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

honojs/honocommit 3a67f7f

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-5428671 days apartHono: Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)
23Monitor

Not on record for this CVE: researcher credit · public bounty program.

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
A user must open a link or visit a page.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: high · data or configuration can be modified
Availability: none

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: Required
Scope: Unchanged
Confidentiality impact: None
Integrity impact: High
Availability impact: None

Weakness class (CWE)

CWE-22 · Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

nvd-secondary

Root cause

A user-supplied file name is joined with the allowed directory, but the result is never checked to confirm it is still inside that directory.

The bug in code

The whole CWE-22 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1const file = path.join(ROOT, req.query.name);
2res.sendFile(file);

Fixed

1const file = path.resolve(ROOT, req.query.name);
2if (!file.startsWith(ROOT + path.sep)) {
3  return res.sendStatus(400);
4}
5res.sendFile(file);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log (1)

Fix✗ → ✓Sep 28, 2026, 10:45 PM UTC

For records you follow, these changes also arrive as notifications. →

References

github.com/honojs/hono/commit/3a67f7f3997e1437d108f7bcba2dbcee2df69221

Show all references (2 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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