Summary
Hono: Incomplete fix for CVE-2026-39408: toSSG() still writes files outside the output directory
The fix released for CVE-2026-39408 does not cover every traversal sequence. toSSG() can still write files outside the configured output directory when a route parameter contains consecutive parent-directory segments.
Details
Static site generation builds each output path from the route path and the values supplied through ssgParams, then verifies that the result stays inside the output directory. That check normalizes the path with the same routine that built it, and the routine did not fully collapse runs of consecutive parent-directory segments. A value carrying enough of them produces a path the check accepts, but the filesystem resolves outside the output directory.
The earlier fix handled a single parent-directory segment, so it blocks the sequence reported at the time while leaving longer runs unhandled. The check also treated output directories that differ only 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, slugs coming from a CMS, an API, or user submissions.
Impact
A value reaching ssgParams from an untrusted source can cause build output to be written outside the intended output directory, carrying whatever content the route handler produced.
This may lead to:
- files being created or overwritten elsewhere in the build environment
- generated artifacts or deployment output being altered
This affects build-time static site generation only; request-time routing is not affected. Applications whose ssgParams values are entirely developer-controlled are not affected.
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
CVE-2026-84365 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.13.5); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-84365? CVE-2026-84365 is a medium-severity path traversal vulnerability in hono (npm), affecting versions < 4.13.5. It is fixed in 4.13.5. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-84365? CVE-2026-84365 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of hono are affected by CVE-2026-84365? hono (npm) versions < 4.13.5 is affected.
- Is there a fix for CVE-2026-84365? Yes. CVE-2026-84365 is fixed in 4.13.5. Upgrade to this version or later.
- Is CVE-2026-84365 exploitable, and should I be worried? Whether CVE-2026-84365 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-84365 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-84365? Upgrade
honoto 4.13.5 or later.