CWE-277: Insecure Inherited Permissions

What is Insecure Inherited Permissions?

• Overview: Insecure Inherited Permissions is a vulnerability where a software product sets permissions that are too broad or insecure, and these permissions are inherited by newly created objects or files, potentially leading to unauthorized access.

• Exploitation Methods:

• Attackers can exploit this vulnerability by accessing newly created objects that have inherited weak permissions, allowing them to read, modify, or delete sensitive data.
• Common attack patterns include escalating privileges by exploiting files or processes with overly permissive access controls, and accessing confidential information due to insufficient restrictions.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to sensitive data, unauthorized modification or deletion of data, and potential system compromise.
• Potential cascading effects include privilege escalation, further unauthorized access, and the ability to execute malicious code.
• Business impact can include data breaches, loss of customer trust, legal liabilities, and financial losses due to compromised systems.

• Prevention Guidelines:

• Specific code-level fixes include explicitly defining secure permissions for objects and files at creation, rather than relying on inherited defaults.
• Security best practices involve regularly auditing and reviewing permission settings, adhering to the principle of least privilege, and ensuring that inherited permissions are appropriate for the security context.
• Recommended tools and frameworks include using access control mechanisms provided by the operating system or language runtime, and employing security-focused libraries that enforce permission checks.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

const fs = require('fs');

function createFile(filename) {
    // Create a new file with default permissions
    fs.writeFileSync(filename, 'Sensitive data');
}

// This function creates a file using the system's default umask,
// which can result in overly permissive file permissions.
createFile('sensitiveData.txt');

Explanation:

In the vulnerable code example above, the fs.writeFileSync method is used to create a file without specifying file permissions. By default, Node.js will use the system's umask setting to determine the file permissions, which might lead to the file being created with permissions that are too permissive. This can allow unauthorized users to read or modify the file, leading to a potential security breach.

How to fix Insecure Inherited Permissions?

To fix this issue, you should explicitly set the file permissions when creating the file. This ensures that the file has restrictive permissions, such as read/write for the owner only, regardless of the system's umask settings.

Fixed Code Example

const fs = require('fs');

function createFileSecure(filename) {
    // Create a new file with restrictive permissions
    // 0o600 - sets the file permission to be readable and writable only by the owner
    fs.writeFileSync(filename, 'Sensitive data', { mode: 0o600 });
}

// This function now creates the file with restrictive permissions
createFileSecure('sensitiveData.txt');

Explanation:

In the fixed code example, the fs.writeFileSync function includes a mode option set to 0o600. This explicitly sets the file permissions to be readable and writable only by the file owner. By doing this, you ensure that sensitive data stored in the file is protected from unauthorized access, regardless of the system's default umask settings. This practice helps prevent data leakage and unauthorized modification.