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Mitigation Strategies Analysis for mikel/mail

Mitigation Strategy: Validate Email Inputs

  • Description:

    1. Identify all email input points: Locate every place in your application where users can provide email-related data (e.g., registration forms, contact forms, password reset requests, email composition features).
    2. Implement server-side validation: Use regular expressions or dedicated email validation libraries within your application's backend code to check if the provided input conforms to a valid email address format.
      • Example (Ruby using regex): input_email =~ /\A[\w+\-.]+@[a-z\d\-]+(\.[a-z\d\-]+)*\.[a-z]+\z/i
    3. Reject invalid inputs: If the email input fails validation, reject it immediately and provide clear error messages to the user, guiding them to correct the input.

  • List of Threats Mitigated:

    • Email Header Injection - Severity: High
    • Spam/Abuse via Form Submission - Severity: Medium
    • Data Integrity Issues (Invalid Email Addresses) - Severity: Low

  • Impact:

    • Email Header Injection: Significantly reduces the risk by preventing attackers from injecting malicious headers through manipulated email input fields.
    • Spam/Abuse via Form Submission: Reduces the likelihood of automated scripts submitting invalid or malicious email addresses for spamming or other abusive purposes.
    • Data Integrity Issues (Invalid Email Addresses): Prevents storage of invalid email addresses, ensuring reliable communication and data quality.

  • Currently Implemented:

    • Basic email format validation using regular expressions is implemented in user registration and contact forms.

  • Missing Implementation:

    • More robust validation using dedicated email validation libraries for edge cases and internationalized email addresses.
    • Validation is not consistently applied across all email input points in the application (e.g., password reset form might lack strict validation).

Mitigation Strategy: Sanitize Email Inputs for Header Inclusion

  • Description:

    1. Identify user inputs used in headers: Pinpoint all instances where user-provided data is incorporated into email headers (e.g., Subject, custom headers).
    2. Use mail gem's encoding methods: Utilize the mail gem's built-in encoding functionalities (like Mail::Encodings.b_value_encode or Mail::Encodings.q_value_encode) when constructing headers with user input. These methods properly encode special characters to prevent header injection.
    3. Limit header usage from user input: Minimize the use of user input directly in headers. If possible, use predefined headers or construct headers programmatically based on validated and sanitized data.

  • List of Threats Mitigated:

    • Email Header Injection - Severity: High

  • Impact:

    • Email Header Injection: Drastically reduces the risk by ensuring that user-provided data is properly encoded and cannot be interpreted as email header commands, preventing attackers from manipulating email behavior.

  • Currently Implemented:

    • mail gem is used for email sending, but explicit encoding of user-provided subject lines is not consistently applied.

  • Missing Implementation:

    • Implementation of Mail::Encodings or similar encoding methods for all user-provided data used in email headers, especially the Subject line in contact forms and password reset emails.
    • Review and refactor code to minimize direct inclusion of user input in headers where possible.

Mitigation Strategy: Sanitize Attachment Filenames

  • Description:

    1. Intercept attachment uploads: When users upload files as attachments, intercept the filename before it's processed or stored.
    2. Implement filename sanitization: Apply a sanitization process to the filename:
      • Remove or replace dangerous characters: Remove or replace characters like /, \, .., :, ;, <, >, &, |, control characters, and spaces with safe alternatives (e.g., underscores, dashes).
      • Limit filename length: Enforce a maximum filename length to prevent buffer overflow vulnerabilities in systems processing filenames.
      • Consider using UUIDs: Generate a UUID (Universally Unique Identifier) as the internal filename for storage and processing. Store the original sanitized filename separately for display purposes.

  • List of Threats Mitigated:

    • File Path Traversal - Severity: High
    • Remote Code Execution (in some scenarios) - Severity: High (depending on application logic and file processing)
    • Cross-Site Scripting (XSS) via Filename (in specific contexts) - Severity: Medium

  • Impact:

    • File Path Traversal: Significantly reduces the risk by preventing attackers from manipulating filenames to access or overwrite files outside of the intended attachment storage directory.
    • Remote Code Execution: Reduces the risk in scenarios where filename processing might be vulnerable to exploits based on specially crafted filenames.
    • Cross-Site Scripting (XSS) via Filename: Reduces the risk in specific contexts where filenames are directly displayed in web pages without proper encoding, potentially leading to XSS if malicious filenames are crafted.

  • Currently Implemented:

    • Basic file type validation is implemented for attachments (e.g., allowing only images and documents).

  • Missing Implementation:

    • Robust filename sanitization is not implemented. Filenames are stored as uploaded, potentially containing harmful characters.
    • UUIDs are not used for internal storage of attachments; original filenames are used directly.

Mitigation Strategy: HTML Sanitization for Email Body Display

  • Description:

    1. Identify email body display points: Locate where email bodies (especially HTML emails) parsed by the mail gem are displayed in your application (e.g., email inbox view, notification displays).
    2. Integrate an HTML sanitization library: Choose a robust HTML sanitization library for your programming language (e.g., rails-html-sanitizer or sanitize in Ruby, bleach in Python, DOMPurify in JavaScript for client-side).
    3. Sanitize HTML email bodies before display: Before rendering HTML email content in a browser, pass it through the HTML sanitization library. Configure the library to remove or neutralize potentially malicious HTML tags, attributes, and JavaScript code (e.g., <script>, <iframe>, onclick, javascript: URLs).

  • List of Threats Mitigated:

    • Cross-Site Scripting (XSS) - Severity: High
    • Phishing and Content Spoofing - Severity: Medium

  • Impact:

    • Cross-Site Scripting (XSS): Significantly reduces the risk by preventing attackers from injecting malicious JavaScript or HTML into emails that could be executed in users' browsers when viewing the email.
    • Phishing and Content Spoofing: Reduces the risk of attackers using HTML emails to create convincing phishing attempts or spoof legitimate content within the email display.

  • Currently Implemented:

    • Plain text emails are displayed as is. HTML emails are displayed without sanitization.

  • Missing Implementation:

    • Integration of an HTML sanitization library to sanitize HTML email bodies before displaying them to users.

Mitigation Strategy: Attachment Scanning for Malware

  • Description:

    1. Choose a malware scanning solution: Select an antivirus or malware scanning service or library that can be integrated into your application's workflow. Options include cloud-based scanning APIs or on-premise solutions.
    2. Integrate scanning into attachment processing: Modify your application to automatically scan all incoming and outgoing email attachments using the chosen malware scanning solution before they are stored, processed, or delivered.
    3. Define actions for malware detection: Determine how to handle attachments identified as malicious:
      • Quarantine: Move the email and attachment to a quarantine area for administrator review.
      • Reject: Reject the email entirely and notify the sender (if applicable and safe to do so).
      • Remove attachment: Remove the malicious attachment and deliver the email without it, notifying the recipient about the removed attachment.

  • List of Threats Mitigated:

    • Malware Distribution via Email Attachments - Severity: High
    • Compromise of User Systems - Severity: High
    • Data Breach via Malware - Severity: High

  • Impact:

    • Malware Distribution via Email Attachments: Significantly reduces the risk of your application being used to distribute malware through email attachments.
    • Compromise of User Systems: Protects users of your application from being infected by malware delivered via email attachments.
    • Data Breach via Malware: Reduces the risk of malware infections leading to data breaches or system compromise within your application's environment.

  • Currently Implemented:

    • No malware scanning is currently implemented for email attachments.

  • Missing Implementation:

    • Integration of a malware scanning solution into the email attachment processing workflow for both incoming and outgoing emails.
    • Definition of policies and procedures for handling emails with malicious attachments.

Mitigation Strategy: Secure SMTP Configuration

  • Description:

    1. Enable TLS/STARTTLS: Configure the mail gem to use TLS/STARTTLS for SMTP connections. This encrypts the communication channel between your application and the mail server.
      • In mail gem configuration: delivery_method :smtp, address: 'smtp.example.com', port: 587, enable_starttls_auto: true
    2. Verify SSL/TLS certificate: Enable SSL/TLS certificate verification to ensure you are connecting to the legitimate mail server and prevent man-in-the-middle attacks.
      • In mail gem configuration: delivery_method :smtp, ..., ssl: { verify_mode: OpenSSL::SSL::VERIFY_PEER }
    3. Securely store SMTP credentials: Do not hardcode SMTP credentials directly in your application code. Use environment variables, secure configuration management systems (like HashiCorp Vault), or encrypted configuration files to store credentials securely.

  • List of Threats Mitigated:

    • Man-in-the-Middle (MITM) Attacks - Severity: High
    • Credential Exposure - Severity: High
    • Data Interception (Email Content and Credentials) - Severity: High

  • Impact:

    • Man-in-the-Middle (MITM) Attacks: Significantly reduces the risk by encrypting communication and verifying the mail server's identity, making it much harder for attackers to intercept or tamper with email traffic.
    • Credential Exposure: Reduces the risk of SMTP credentials being exposed in source code or configuration files by promoting secure storage practices.
    • Data Interception (Email Content and Credentials): Protects sensitive email content and SMTP credentials from being intercepted during transmission.

  • Currently Implemented:

    • SMTP is used for sending emails, and STARTTLS is enabled.

  • Missing Implementation:

    • SSL/TLS certificate verification is not explicitly enabled.
    • SMTP credentials are stored in environment variables, but could be further secured using a dedicated secret management system.