CWE-404: Improper Resource Shutdown or Release

What is Improper Resource Shutdown or Release?

• Overview: Improper Resource Shutdown or Release (CWE-404) occurs when software fails to release or incorrectly releases a resource, such as memory, files, or network connections, leading to resource leaks or unintended states.

• Exploitation Methods:

• Attackers can exploit this vulnerability by causing a denial of service through resource exhaustion.
• Common attack patterns include triggering resource leaks by repeatedly requesting resource allocation without proper release.

• Security Impact:

• Direct consequences include memory leaks, file descriptor leaks, or other resource leaks, leading to degraded performance or application crashes.
• Potential cascading effects include making the system vulnerable to further attacks due to reduced availability of resources.
• Business impact can include loss of service availability, increased costs due to resource wastage, and potential reputational damage.

• Prevention Guidelines:

• Specific code-level fixes include ensuring proper use of try-finally blocks, destructors, or equivalent structures to guarantee resource release.
• Security best practices involve thorough code reviews and testing to identify and correct paths that do not properly release resources.
• Recommended tools and frameworks include static analysis tools to detect resource management issues and using resource management libraries that automate resource release.

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Technical Details

Likelihood of Exploit: Medium

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

Here is the revised content with improvements addressing the mentioned issues:

const fs = require('fs');

function readFile(filePath) {
    fs.open(filePath, 'r', (err, fd) => {
        if (err) {
            console.error(`An error occurred: \${err}`);
            return;
        }
        const buffer = Buffer.alloc(1024);
        fs.read(fd, buffer, 0, buffer.length, null, (err, bytesRead, buffer) => {
            if (err) {
                console.error(`An error occurred: \${err}`);
                return;
            }
            console.log(buffer.toString('utf8', 0, bytesRead));
            // Vulnerability: The file descriptor is not closed, leading to a potential resource leak
        });
    });
}

In this JavaScript example, the vulnerability arises because the file descriptor (fd) is not closed after reading the file. This can lead to file descriptor exhaustion, especially in applications that open many files or run for an extended period.

How to fix Improper Resource Shutdown or Release?

The fix involves ensuring that the file descriptor is properly closed after its use. This is done by explicitly calling fs.close() after the file operations are completed. It is crucial to handle the close operation within the callback to ensure it runs regardless of whether the reading was successful or an error occurred.

Fixed Code Example

const fs = require('fs');

function readFile(filePath) {
    fs.open(filePath, 'r', (err, fd) => {
        if (err) {
            console.error(`An error occurred: \${err}`);
            return;
        }
        const buffer = Buffer.alloc(1024);
        fs.read(fd, buffer, 0, buffer.length, null, (err, bytesRead, buffer) => {
            if (err) {
                console.error(`An error occurred: \${err}`);
                fs.close(fd, (closeErr) => {
                    if (closeErr) console.error(`Failed to close file: \${closeErr}`);
                });  // Ensure file descriptor is closed on error
                return;
            }
            console.log(buffer.toString('utf8', 0, bytesRead));
            fs.close(fd, (closeErr) => {
                if (closeErr) console.error(`Failed to close file: \${closeErr}`);
            });  // Ensure file descriptor is closed after operation
        });
    });
}

In this fixed example, the fs.close() function is used to ensure the file descriptor is properly closed after the file reading operations, preventing resource leaks. Proper error handling is also included to make sure the application can gracefully handle errors during the file closing process. This approach ensures that resources are properly released, even if an error occurs during reading.