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By design, the JDBCAppender in Log4j 1.2.x accepts an SQL statement as a configuration parameter where the values to be inserted are converters from PatternLayout. The message converter, %m, is likely to always be included. This allows attackers to manipulate the SQL by entering crafted strings into input fields or headers of an application that are logged allowing unintended SQL queries to be executed. Note this issue only affects Log4j 1.x when specifically configured to use the JDBCAppender, which is not the default. Beginning in version 2.0-beta8, the JDBCAppender was re-introduced with proper support for parameterized SQL queries and further customization over the columns written to in logs. Apache Log4j 1.2 reached end of life in August 2015. Users should upgrade to Log4j 2 as it addresses numerous other issues from the previous versions.
CVSS 3.1 Base Score 9.8. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).
CVSS 2.0 Base Score 6.8. CVSS Attack Vector: network. CVSS Attack Complexity: medium. CVSS Vector: (AV:N/AC:M/Au:N/C:P/I:P/A:P).
In 2008, a large number of web servers were compromised using the same SQL injection attack string. This single string worked against many different programs. The SQL injection was then used to modify the web sites to serve malicious code.
The following code dynamically constructs and executes a SQL query that searches for items matching a specified name. The query restricts the items displayed to those where owner matches the user name of the currently-authenticated user.
...The query that this code intends to execute follows:
SELECT * FROM items WHERE owner = <userName> AND itemname = <itemName>;However, because the query is constructed dynamically by concatenating a constant base query string and a user input string, the query only behaves correctly if itemName does not contain a single-quote character. If an attacker with the user name wiley enters the string:
name' OR 'a'='afor itemName, then the query becomes the following:
SELECT * FROM items WHERE owner = 'wiley' AND itemname = 'name' OR 'a'='a';The addition of the:
OR 'a'='acondition causes the WHERE clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query:
SELECT * FROM items;This simplification of the query allows the attacker to bypass the requirement that the query only return items owned by the authenticated user; the query now returns all entries stored in the items table, regardless of their specified owner.
This code intends to print a message summary given the message ID.
mysql_query("SELECT MessageID, Subject FROM messages WHERE MessageID = '$id'");The programmer may have skipped any input validation on $id under the assumption that attackers cannot modify the cookie. However, this is easy to do with custom client code or even in the web browser.
While $id is wrapped in single quotes in the call to mysql_query(), an attacker could simply change the incoming mid cookie to:
1432' or '1' = '1This would produce the resulting query:
SELECT MessageID, Subject FROM messages WHERE MessageID = '1432' or '1' = '1'Not only will this retrieve message number 1432, it will retrieve all other messages.
In this case, the programmer could apply a simple modification to the code to eliminate the SQL injection:
mysql_query("SELECT MessageID, Subject FROM messages WHERE MessageID = '$id'");However, if this code is intended to support multiple users with different message boxes, the code might also need an access control check (CWE-285) to ensure that the application user has the permission to see that message.
This example attempts to take a last name provided by a user and enter it into a database.
$query = "INSERT INTO last_names VALUES('$userKey', '$name')";# ensure only letters, hyphens and apostrophe are allowedWhile the programmer applies a whitelist to the user input, it has shortcomings. First of all, the user is still allowed to provide hyphens which are used as comment structures in SQL. If a user specifies -- then the remainder of the statement will be treated as a comment, which may bypass security logic. Furthermore, the whitelist permits the apostrophe which is also a data / command separator in SQL. If a user supplies a name with an apostrophe, they may be able to alter the structure of the whole statement and even change control flow of the program, possibly accessing or modifying confidential information. In this situation, both the hyphen and apostrophe are legitimate characters for a last name and permitting them is required. Instead, a programmer may want to use a prepared statement or apply an encoding routine to the input to prevent any data / directive misinterpretations.
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