secure_coding_guidelines
Last updated: 2024-09-17 21:09:16.913402 File source: link on GitLab
Author: @umair-nunet from Issue https://gitlab.com/nunet/nunet-infra/-/issues/97#note_1000806200
Purpose
The purpose of this document is to help developers bring a security mindset to writing code. The idea is that when a developer writes code and is ready to deploy it they do a quick security check to make sure they have done their due diligence in securing their creation. This should be a good guideline when securing application code. Only pay attention to the sections that pertain to code. For example, if you wrote something only has to do with databases, only look at the database portion. There is no need to read about file management unless your code does file management. The list was provided by the Open Web Application Security Project (OWASP) and their best-securing code practices.
Table of Contents
Input Validation
Conduct all data validation on a trusted system (e.g., The server)
Identify all data sources and classify them into trusted and untrusted. Validate all data from untrusted [sources (e.g., Databases, file streams, etc.)]
There should be a centralized input validation routine for the application
Specify proper character sets, such as UTF-8, for all sources of input
Encode data to a common character set before validating (Canonicalize)
All validation failures should result in input rejection
Determine if the system supports UTF-8 extended character sets and if so, validate after UTF-8 decoding is completed
Validate all client-provided data before processing, including all parameters, URLs, and HTTP header content (e.g. Cookie names and values). Be sure to include automated postbacks from JavaScript, Flash, or other embedded code
Verify that header values in both requests and responses contain only ASCII characters
Validate data from redirects (An attacker may submit malicious content directly to the target of the redirect, thus circumventing application logic and any validation performed before the redirect)
Validate for expected data types
Validate data range
Validate data length
Validate all input against a "white" list of allowed characters, whenever possible
If any potentially hazardous characters must be allowed as input, be sure that you implement additional controls like output encoding, secure task specific APIs, and accounting for the utilization of that data throughout the application. Examples of common hazardous characters include: < > " ' % ( ) & + \ ' "
If your standard validation routine cannot address the following inputs, then they should be checked discretely
Check for null bytes (%00)
Check for new line characters (%0d, %0a, \r, \n)
Check for “dot-dot-slash" (../ or ..) path alterations characters. In cases where UTF-8 extended character set encoding is supported, address alternate representation like: %c0%ae%c0%ae/ (Utilize canonicalization to address double encoding or other forms of obfuscation attacks)
Output Encoding
Conduct all encoding on a trusted system (e.g., The server)
Utilize a standard, tested routine for each type of outbound encoding
Contextually output encodes all data returned to the client that originated outside the application's trust boundary. HTML entity encoding is one example but does not work in all cases
Encode all characters unless they are known to be safe for the intended interpreter
Contextually sanitize all output of un-trusted data to queries for SQL, XML, and LDAP
Sanitize all output of un-trusted data to operating system commands
Authentication and Password Management
Require authentication for all pages and resources, except those specifically intended to be public
All authentication controls must be enforced on a trusted system (e.g., The server)
Establish and utilize standard, tested, authentication services whenever possible
Use a centralized implementation for all authentication controls, including libraries that call external authentication services
Segregate authentication logic from the resource being requested and use redirection to and from the centralized authentication control
All authentication controls should fail securely
All administrative and account management functions must be at least as secure as the primary authentication mechanism
If your application manages a credential store, it should ensure that only cryptographically strong one-way salted hashes of passwords are stored and that the table/file that stores the passwords and keys is writeable only by the application. (Do not use the MD5 algorithm if it can be avoided)
Password hashing must be implemented on a trusted system (e.g., The server).
Validate the authentication data only on completion of all data input, especially for sequential authentication implementations
Authentication failure responses should not indicate which part of the authentication data was incorrect. For example, instead of "Invalid username" or "Invalid password", just use "Invalid username and/or password" for both. Error responses must be truly identical in both display and source code
Utilize authentication for connections to external systems that involve sensitive information or functions
Authentication credentials for accessing services external to the application should be encrypted and stored in a protected location on a trusted system (e.g., The server). The source code is NOT a secure location
Use only HTTP POST requests to transmit authentication credentials
Only send non-temporary passwords over an encrypted connection or as encrypted data, such as in an encrypted email. Temporary passwords associated with email resets may be an exception
Enforce password complexity requirements established by policy or regulation. Authentication credentials should be sufficient to withstand attacks typical of the deployed environment's threats. (e.g., requiring the use of alphabetic as well as numeric and/or special characters)
Enforce password length requirements established by policy or regulation. Eight characters are commonly used, but 16 is better or consider the use of multi-word pass phrases
Password entry should be obscured on the user's screen. (e.g., on web forms use the input type "password")
Enforce account disabling after an established number of invalid login attempts (e.g., five attempts is common). The account must be disabled for a period of time sufficient to discourage brute force guessing of credentials, but not so long as to allow for a denial-of-service attack to be performed
Password reset and changing operations require the same level of control as account creation and authentication.
Password reset questions should support sufficiently random answers. (e.g., "favorite book" is a bad question because “The Bible” is a very common answer)
If using email-based resets, only send email to a pre-registered address with a temporary link/password
Temporary passwords and links should have a short expiration time
Enforce the changing of temporary passwords on the next use
Notify users when a password reset occurs
Prevent password re-use
Passwords should be at least one-day-old before they can be changed, to prevent attacks on password re-use
Enforce password changes based on requirements established in policy or regulation. Critical systems may require more frequent changes. The time between resets must be administratively controlled
Disable the "remember me" functionality for password fields
The last use (successful or unsuccessful) of a user account should be reported to the user at their next successful login
Implement monitoring to identify attacks against multiple user accounts, utilizing the same password.
This attack pattern is used to bypass standard lockouts when user IDs can be harvested or guessed
Change all vendor-supplied default passwords and user IDs or disable the associated accounts
Re-authenticate users prior to performing critical operations
Use Multi-Factor Authentication for highly sensitive or high-value transactional accounts
If using third-party code for authentication, inspect the code carefully to ensure it is not affected by any malicious code
Access Control
Use only trusted system objects, e.g. server-side session objects, for making access authorization decisions
Use a single site-wide component to check access authorization. This includes libraries that call external authorization services
Access controls should fail securely
Deny all access if the application cannot access its security configuration information
Enforce authorization controls on every request, including those made by server-side scripts, "includes" and requests from rich client-side technologies like AJAX and Flash
Segregate privileged logic from other application code
Restrict access to files or other resources, including those outside the application's direct control, to only authorized users
Restrict access to protected URLs to only authorized users
Restrict access to protected functions to only authorized users
Restrict direct object references to only authorized users
Restrict access to services to only authorized users
Restrict access to application data to only authorized users
Restrict access to user and data attributes and policy information used by access controls
Restrict access security-relevant configuration information to only authorized users
Server-side implementation and presentation layer representations of access control rules must match
If state data must be stored on the client, use encryption and integrity checking on the server-side to catch state tampering.
Enforce application logic flows to comply with business rules
Limit the number of transactions a single user or device can perform in a given period of time. The transactions/time should be above the actual business requirement, but low enough to deter automated attacks
Use the "referer" header as a supplemental check only, it should never be the sole authorization check, as it is can be spoofed
If long authenticated sessions are allowed, periodically re-validate a user’s authorization to ensure that their privileges have not changed and if they have, log the user out and force them to re-authenticate
Implement account auditing and enforce the disabling of unused accounts (e.g., After no more than 30 days from the expiration of an account’s password.)
The application must support disabling of accounts and terminating sessions when authorization ceases (e.g., Changes to the role, employment status, business process, etc.) Service accounts or accounts supporting connections to or from external systems should have the least privilege possible
Create an Access Control Policy to document an application's business rules, data types and access authorization criteria and/or processes so that access can be properly provisioned and controlled. This includes identifying access requirements for both the data and system resources
Cryptographic Practices
All cryptographic functions used to protect secrets from the application user must be implemented on a trusted system (e.g., The server)
Protect master secrets from unauthorized access
Cryptographic modules should fail securely
All random numbers, random file names, random GUIDs, and random strings should be generated using the cryptographic module’s approved random number generator when these random values are intended to be un-guessable
Cryptographic modules used by the application should be compliant to FIPS 140-2 or an equivalent standard. (See http://csrc.nist.gov/groups/STM/cmvp/validation.html)
Establish and utilize a policy and process for how cryptographic keys will be managed
Error Handling and Logging
Do not disclose sensitive information in error responses, including system details, session identifiers, or account information
Use error handlers that do not display debugging or stack trace information
Implement generic error messages and use custom error pages
The application should handle application errors and not rely on the server configuration
Properly free allocated memory when error conditions occur
Error handling logic associated with security controls should deny access by default
All logging controls should be implemented on a trusted system (e.g., The server)
Logging controls should support both the success and failure of specified security events
Ensure logs contain important log event data
Ensure log entries that include un-trusted data will not execute as code in the intended log viewing interface or software
Restrict access to logs to only authorized individuals
Utilize a master routine for all logging operations
Do not store sensitive information in logs, including unnecessary system details, session identifiers or passwords
Ensure that a mechanism exists to conduct log analysis
Log all input validation failures
Log all authentication attempts, especially failures
Log all access control failures
Log all apparent tampering events, including unexpected changes to state data
Log attempts to connect with invalid or expired session tokens
Log all system exceptions
Log all administrative functions, including changes to the security configuration settings
Log all backend TLS connection failures
Log cryptographic module failures
Use a cryptographic hash function to validate log entry integrity
Data Protection
Implement least privilege, restrict users to only the functionality, data, and system information that is required to perform their tasks
Protect all cached or temporary copies of sensitive data stored on the server from unauthorized access and purge those temporary working files as soon as they are no longer required.
Encrypt highly sensitive stored information, like authentication verification data, even on the server-side. Always use well-vetted algorithms, see "Cryptographic Practices" for additional guidance
Protect server-side source code from being downloaded by a user
Do not store passwords, connection strings or other sensitive information in clear text or in any non-cryptographically secure manner on the client-side. This includes embedding in insecure formats like MS ViewState, Adobe flash, or compiled code
Remove comments in user-accessible production code that may reveal backend system or other sensitive information
Remove unnecessary application and system documentation as this can reveal useful information to attackers
Do not include sensitive information in HTTP GET request parameters
Disable auto-complete features on forms expected to contain sensitive information, including authentication
Disable client-side caching on pages containing sensitive information. Cache-Control: no-store, may be used in conjunction with the HTTP header control "Pragma: no-cache", which is less effective, but is HTTP/1.0 backward compatible
The application should support the removal of sensitive data when that data is no longer required. (e.g. personal information or certain financial data) -Implement appropriate access controls for sensitive data stored on the server. This includes cached data, temporary files, and data that should be accessible only by the specific system user
Communication Security
Implement encryption for the transmission of all sensitive information. This should include TLS for protecting the connection and may be supplemented by discrete encryption of sensitive files or non HTTP based connections
TLS certificates should be valid and have the correct domain name, not be expired, and be installed with intermediate certificates when required
Failed TLS connections should not fall back to an insecure connection
Utilize TLS connections for all content requiring authenticated access and for all other sensitive information
Utilize TLS for connections to external systems that involve sensitive information or functions
Utilize a single standard TLS implementation that is configured appropriately
Specify character encodings for all connections
Filter parameters containing sensitive information from the HTTP referer, when linking to external sites
System Configuration
Ensure servers, frameworks, and system components are running the latest approved version
Ensure servers, frameworks, and system components have all patches issued for the version in use
Turn off directory listings
Restrict the web server, process, and service accounts to the least privileges possible
When exceptions occur, fail securely
Remove all unnecessary functionality and files
Remove test code or any functionality not intended for production, prior to deployment
Prevent disclosure of your directory structure in the robots.txt file by placing directories not intended for public indexing into an isolated parent directory. Then "Disallow" that entire parent directory in the robots.txt file rather than Disallowing each individual directory
Define which HTTP methods, Get or Post, the application will support and whether it will be handled differently on different pages in the application
Disable unnecessary HTTP methods, such as WebDAV extensions. If an extended HTTP method that supports file handling is required, utilize a well-vetted authentication mechanism
If the web server handles both HTTP 1.0 and 1.1, ensure that both are configured in a similar manner or insure that you understand any difference that may exist (e.g. handling of extended HTTP methods)
Remove unnecessary information from HTTP response headers related to the OS, web-server version, and application frameworks
The security configuration store for the application should be able to be output in the human-readable form to support auditing
Implement an asset management system and register system components and software in it
Isolate development environments from the production network and provide access only to authorized development and test groups. Development environments are often configured less securely than production environments and attackers may use this difference to discover shared weaknesses or as an avenue for exploitation
Implement a software change control system to manage and record changes to the code both in development and production
Clear your system of any unnecessary components and ensure all working software is updated with current versions and patches.
If you work in multiple environments, make sure you’re managing your development and production environments securely.
Outdated software is a major source of vulnerabilities and security breaches.
Software updates include patches that fix vulnerabilities, making regular updates one of the most vital, secure coding practices.
A patch management system may help your business to keep on top of updates.
Database Security
Use strongly typed parameterized queries
Utilize input validation and output encoding and be sure to address meta characters. If these fail, do not run the database command
Ensure that variables are strongly typed
The application should use the lowest possible level of privilege when accessing the database
Use secure credentials for database access
Connection strings should not be hard coded within the application. Connection strings should be stored in a separate configuration file on a trusted system and they should be encrypted.
Use stored procedures to abstract data access and allow for the removal of permissions to the base tables in the database
Close the connection as soon as possible
Remove or change all default database administrative passwords. Utilize strong passwords/phrases or implement multi-factor authentication
Turn off all unnecessary database functionality (e.g., unnecessary stored procedures or services, utility packages, install only the minimum set of features and options required (surface area reduction))
Remove unnecessary default vendor content (e.g., sample schemas)
Disable any default accounts that are not required to support business requirements
The application should connect to the database with different credentials for every trust distinction (e.g., user, read-only user, guest, administrators)
File Management
Do not pass user supplied data directly to any dynamic including function
Require authentication before allowing a file to be uploaded
Limit the type of files that can be uploaded to only those types that are needed for business purposes
Validate uploaded files are the expected type by checking file headers. Checking for file type by extension alone is not sufficient
Do not save files in the same web context as the application. Files should either go to the content server or in the database.
Prevent or restrict the uploading of any file that may be interpreted by the web server.
Turn off execution privileges on file upload directories
Implement safe uploading in UNIX by mounting the targeted file directory as a logical drive using the associated path or the chrooted environment
When referencing existing files, use a white list of allowed file names and types. Validate the value of the parameter being passed and if it does not match one of the expected values, either reject it or use a hard-coded default file value for the content instead
Do not pass user-supplied data into a dynamic redirect. If this must be allowed, then the redirect should accept only validated, relative path URLs
Do not pass directory or file paths, use index values mapped to a pre-defined list of paths
Never send the absolute file path to the client
Ensure application files and resources are read-only
Scan user uploaded files for viruses and malware
Memory Management
Utilize input and output control for un-trusted data
Double-check that the buffer is as large as specified
When using functions that accept a number of bytes to copy, such as strncpy(), be aware that if the destination buffer size is equal to the source buffer size, it may not NULL-terminate the string
Check buffer boundaries if calling the function in a loop and make sure there is no danger of writing past the allocated space
Truncate all input strings to a reasonable length before passing them to the copy and concatenation functions
Specifically close resources, don’t rely on garbage collection. (e.g., connection objects, file handles, etc.)
Use non-executable stacks when available
Avoid the use of known vulnerable functions (e.g., printf, strcat, strcpy, etc.)
Properly free allocated memory upon the completion of functions and at all exit points
General Coding Practices
Use tested and approved managed code rather than creating new unmanaged code for common tasks
Utilize task-specific built-in APIs to conduct operating system tasks. Do not allow the application to issue commands directly to the Operating System, especially through the use of application-initiated command shells
Use checksums or hashes to verify the integrity of interpreted code, libraries, executables, and configuration files
Utilize locking to prevent multiple simultaneous requests or use a synchronization mechanism to prevent race conditions
Protect shared variables and resources from inappropriate concurrent access
Explicitly initialize all your variables and other data stores, either during declaration or just before the first usage
In cases where the application must run with elevated privileges, raise privileges as late as possible, and drop them as soon as possible
Avoid calculation errors by understanding your programming language's underlying representation and how it interacts with numeric calculation. Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, "not-a-number" calculations, and how your language handles numbers that are too large or too small for its underlying representation
Do not pass user-supplied data to any dynamic execution function
Restrict users from generating new code or altering existing code
Review all secondary applications, third-party code, and libraries to determine the business necessity and validate safe functionality, as these can introduce new vulnerabilities
Implement safe updating. If the application will utilize automatic updates, then use cryptographic signatures for your code and ensure your download clients verify those signatures. Use encrypted channels to transfer the code from the host server
References
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