Hash Extension

When your application relies on sha256(SECRET+message) to create/verify cookies it is probably vulnerable to this attack. Vulnerable functions are MD5, SHA1 and SHA-2. If the message and length of the secret are known, we can append additional data and still produce a valid hash. This only works if a secret is prepended. Good tools to exploit this kind of vulnerability are hash_extender and HashPump.

SQL Truncation

Sometime data gets truncated in the database (because a field has a fixed length that it is exceeded), so you could register 1 even when already exists, overwriting the entry. If a login functions that only checks for the existence of at least one entry for the email & password, we can login as admin.

On JWT Cookies some Algorithms don't use the full payload while signing. E.g. this gets truncated after 70 characters:

$json = $this->toJson();
$jsonb64 = base64_encode($json);
$signature = base64_encode(password_hash(SECRET.$json, PASSWORD_BCRYPT));
setcookie('PHPSESSID', "${jsonb64}.${signature}", time()+60*60*24, '/');


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