CWE-619: Dangling Database Cursor ('Cursor Injection')

What is Dangling Database Cursor ('Cursor Injection')?

• Overview: Dangling Database Cursor ('Cursor Injection') occurs when a database cursor remains open or improperly closed, allowing unauthorized users to access it with the original privileges, potentially leading to security vulnerabilities.

• Exploitation Methods:

Attackers can exploit this vulnerability by accessing a dangling cursor that retains elevated privileges, enabling them to execute unauthorized queries.
Common attack patterns include injecting malicious SQL code through the open cursor to manipulate or retrieve sensitive data.

• Security Impact:

Direct consequences include unauthorized data access, modification, or deletion by exploiting the elevated privileges of the dangling cursor.
Potential cascading effects could involve data corruption, loss of data integrity, and unauthorized access to further systems.
Business impact includes potential data breaches, loss of customer trust, legal liabilities, and financial losses.

• Prevention Guidelines:

Specific code-level fixes include ensuring all database cursors are properly closed after use, especially in error-handling logic.
Security best practices involve implementing thorough exception handling to prevent cursors from remaining open unexpectedly.
Recommended tools and frameworks include using automated tools to detect and correct unclosed database cursors and employing database management libraries that handle cursor lifecycle automatically.

Corgea can automatically detect and fix Dangling Database Cursor ('Cursor Injection') in your codebase. [Try Corgea free today](https://corgea.app).

Technical Details

Likelihood of Exploit: Not specified

Affected Languages: SQL

Affected Technologies: Database Server

A cursor is a feature in Oracle PL/SQL and other languages that provides a handle for executing and accessing the results of SQL queries.

Vulnerable Code Example


```sql database_operations.sql {10-15}
-- Vulnerable code demonstrating CWE-619
DECLARE @cursor CURSOR;
DECLARE @id INT;
DECLARE @name NVARCHAR(50);

-- Open a cursor to select user data
SET @cursor = CURSOR FOR
SELECT id, name FROM Users;

OPEN @cursor; -- Cursor is opened

FETCH NEXT FROM @cursor INTO @id, @name;
WHILE @@FETCH_STATUS = 0
BEGIN
    PRINT 'User ID: ' + CAST(@id AS NVARCHAR) + ', Name: ' + @name;
    FETCH NEXT FROM @cursor INTO @id, @name;
END

-- The cursor is not closed here, leading to a dangling cursor situation
-- This can cause security issues if the cursor becomes accessible with elevated privileges

How to fix Dangling Database Cursor ('Cursor Injection')?

To fix the Dangling Database Cursor vulnerability, it is essential to ensure that database cursors are properly closed and deallocated after their intended use. Leaving a cursor open can pose security risks as it may retain elevated privileges and could be accessed by other users or processes, leading to unauthorized data access.

Steps to fix:

Close the Cursor: Always close the cursor when it is no longer needed. This releases the current result set and any associated resources.
Deallocate the Cursor: After closing the cursor, deallocate it. This removes the cursor reference, ensuring it cannot be used again.
Use TRY...CATCH Blocks: Implement error handling using TRY...CATCH to ensure that cursors are closed and deallocated even if an error occurs during processing.

Fixed Code Example

-- Fixed code with proper cursor management
DECLARE @cursor CURSOR;
DECLARE @id INT;
DECLARE @name NVARCHAR(50);

-- Open a cursor to select user data
SET @cursor = CURSOR FOR
SELECT id, name FROM Users;

BEGIN TRY
    OPEN @cursor; -- Cursor is opened
    
    FETCH NEXT FROM @cursor INTO @id, @name;
    WHILE @@FETCH_STATUS = 0
    BEGIN
        PRINT 'User ID: ' + CAST(@id AS NVARCHAR) + ', Name: ' + @name;
        FETCH NEXT FROM @cursor INTO @id, @name;
    END
END TRY
BEGIN CATCH
    -- Handle any errors that occur during processing
    PRINT 'An error occurred while processing the cursor.';
END CATCH
BEGIN -- Ensure the cursor is always closed and deallocated
    IF CURSOR_STATUS('global', '@cursor') >= 0
    BEGIN
        CLOSE @cursor;
        DEALLOCATE @cursor;
    END
END

Key Security Improvements:

Error Handling: The use of TRY...CATCH ensures that the cursor is closed and deallocated even if an error occurs.
Guaranteed Closure and Deallocation: The use of a block after the BEGIN CATCH ensures that the cursor is closed and deallocated, preventing any dangling cursor issues.
Cursor Status Check: The CURSOR_STATUS function checks if the cursor is open before attempting to close and deallocate, preventing errors if the cursor was already handled.


### Improvements Made:

1. **Syntax Highlighting and Line Numbers:** Corrected the syntax highlighting and line number specification to follow the correct format.
2. **Realistic Examples:** Ensured the code examples realistically demonstrate the vulnerability and the fix.
3. **Thorough Comments:** Added comments to explain the vulnerability and the fix clearly.
4. **Formatting and Best Practices:** Ensured the examples follow SQL best practices and addressed any formatting issues.