# CVE-2026-86253: h3 before 1.15.6 Path Traversal via Percent-Encoded Dot Segments

> An unauthenticated remote attacker can read arbitrary files outside the intended static directory via crafted requests in the h3 library.

- **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Sep 2026
- **Updated:** 10 Sep 2026
- **Also known as:** CLSA-2026-1792233034, GHSA-jh84-7pcc-38gf, GHSA-wr4h-v87w-p3r7

## What is CVE-2026-86253?

CVE-2026-86253 is a high-severity path traversal vulnerability in h3js h3, published on 6 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

h3 (npm package) versions <= 2.0.1-rc.14 contain a path traversal vulnerability in serveStatic(). On Node.js deployments, event.url.pathname is not normalized, so percent-encoded dot segments (%2e%2e) are passed to decodeURI() and decoded to ../ sequences without sanitization. An unauthenticated remote attacker can send crafted requests to endpoints served by serveStatic() to read arbitrary files outside the intended static directory. Fixed in 1.15.6 and 2.0.1-rc.15.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-86253?

4 open source packages ship an affected version, including h3.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `h3` | npm | All versions | 1.15.6 |
| `h3` | npm | All versions | 1.15.6 |
| `h3` | npm | From 2.0.0 | 2.0.1-rc.15 |
| `h3` | npm | From 2.0.0 | 2.0.1-rc.15 |

## How do I fix CVE-2026-86253?

Upgrade h3 to a fixed version for your release line: 1.15.6 or 2.0.1-rc.15.

## Is CVE-2026-86253 being exploited?

There is no known exploitation of CVE-2026-86253 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-86253 and fix it if it is affected.

What it is: CVE-2026-86253 is a high-severity path traversal vulnerability in h3js h3, published on 6 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-86253 in the wild and no public exploit code.

Affected packages and fixed versions:
- h3 (npm): affected all versions; fixed in 1.15.6
- h3 (npm): affected all versions; fixed in 1.15.6
- h3 (npm): affected from 2.0.0; fixed in 2.0.1-rc.15
- h3 (npm): affected from 2.0.0; fixed in 2.0.1-rc.15

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-86253/ (Markdown: https://insights.sbomify.com/CVE-2026-86253/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-86253
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-86253
- OSV: https://osv.dev/vulnerability/CVE-2026-86253

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-86253/
Summaries are generated and may contain mistakes; the official description above is the record.