We need to understand that client side controls like client based input validation, hidden fields and interface controls provide little if any security benefit.
Secure Coding Practices Checklist
Input Validation:
Conduct all data validation on a trusted system (e.g., The server)
Identify all data sources and validate all data from untrusted sources (e.g., Databases, file streams, etc.)
There should be a centralized input validation
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 including all parameters, URLs and HTTP header
content (e.g. Cookie names and values). Be sure to include automated post backs 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
o Check for null bytes ()
o Check for new line characters (%0d, %0a, \r, \n)
o 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 encode 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 commandsNovember 2010
Version 2.0 6
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 oneway salted hashes of passwords are stored and that the table/file that stores the passwords and keys is
write-able 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 that are typical of the threats in the deployed
environment. (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 is
commonly used, but 16 is better or consider the use of multi-w ord 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 controls 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 useNovember 2010
Version 2.0 7
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 "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
Session Management:
Use the server or framework’s session management controls. The application should only recognize
these session identifiers as valid
Session identifier creation must always be done on a trusted system (e.g., The server)
Session management controls should use well vetted algorithms that ensure sufficiently random
session identifiers
Set the domain and path for cookies containing authenticated session identifiers to an appropriately
restricted value for the site
Logout functionality should fully terminate the associated session or connection
Logout functionality should be available from all pages protected by authorization
Establish a session inactivity timeout that is as short as possible, based on balancing risk and business
functional requirements. In most cases it should be no more than several hours
Disallow persistent logins and enforce periodic session terminations, even when the session is active.
Especially for applications supporting rich network connections or connecting to critical systems.
Termination times should support business requirements and the user should receive sufficient
notification to mitigate negative impacts
If a session was established before login, close that session and establish a new session after a
successful login
Generate a new session identifier on any re-authentication
Do not allow concurrent logins with the same user ID
Do not expose session identifiers in URLs, error messages or logs. Session identifiers should only be
located in the HTTP cookie header. For example, do not pass session identifiers as GET parameters
Protect server side session data from unauthorized access, by other users of the server, by
implementing appropriate access controls on the server
Generate a new session identifier and deactivate the old one periodically. (This can mitigate certain
session hijacking scenarios where the original identif ier was compromised)
Generate a new session identifier if the connection security changes from HTTP to HTTPS, as can
occur during authentication. Within an application, it is recommended to consistently utilize HTTPS
rather than switching between HTTP to HTTPS.November 2010
Version 2.0 8
Supplement standard session management for sensitive server-side operations, like account
management, by utilizing per-session strong random tokens or parameters. This method can be used
to prevent Cross Site Request Forgery attacks
Supplement standard session management for highly sensitive or critical operations by utilizing perrequest, as opposed to per-session, strong random tokens or parameters
Set the "secure" attribute for cookies transmitted over an TLS connection
Set cookies with the HttpOnly attribute, unless you specifically require client-side scripts within your
application to read or set a cookie's value
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 role, employment status, business process, etc.)
Service accounts or accounts supporting connections to or from external systems should have the least
privilege possibleNovember 2010
Version 2.0 9
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 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 integrityNovember 2010
Version 2.0 10
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 a 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 noncryptographically 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 specific system users
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 nonHTTP 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 in 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 manor
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 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
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 include 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 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 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
