OWASP Secure Coding Practices Checklist

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This is a copy of the SCP checklist. For the project, see OWASP Secure Coding Practices - Quick Reference Guide.

Input Validation

1. Conduct all data validation on a trusted system (e.g., The server)

2. Identify all data sources and classify them into trusted and untrusted. Validate all data from untrusted sources (e.g., Databases, file streams, etc.)

3. There should be a centralized input validation routine for the application

4. Specify proper character sets, such as UTF-8, for all sources of input

5. Encode data to a common character set before validating (Canonicalize)

6. All validation failures should result in input rejection

7. Determine if the system supports UTF-8 extended character sets and if so, validate after UTF-8 decoding is completed

8. 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 post backs from JavaScript, Flash or other embedded code

9. Verify that header values in both requests and responses contain only ASCII characters

10. 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)

11. Validate for expected data types

12. Validate data range

13. Validate data length

14. Validate all input against a "white" list of allowed characters, whenever possible

15. 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: < > " ' % ( ) & + \ \' \"

16. 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

17. Conduct all encoding on a trusted system (e.g., The server)

18. Utilize a standard, tested routine for each type of outbound encoding

19. 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

20. Encode all characters unless they are known to be safe for the intended interpreter

21. Contextually sanitize all output of un-trusted data to queries for SQL, XML, and LDAP

22. Sanitize all output of un-trusted data to operating system commands

Authentication and Password Management

23. Require authentication for all pages and resources, except those specifically intended to be public

24. All authentication controls must be enforced on a trusted system (e.g., The server)

25. Establish and utilize standard, tested, authentication services whenever possible

26. Use a centralized implementation for all authentication controls, including libraries that call external authentication services

27. Segregate authentication logic from the resource being requested and use redirection to and from the centralized authentication control

28. All authentication controls should fail securely

29. All administrative and account management functions must be at least as secure as the primary authentication mechanism

30. 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 write-able only by the application. (Do not use the MD5 algorithm if it can be avoided)

31. Password hashing must be implemented on a trusted system (e.g., The server).

32. Validate the authentication data only on completion of all data input, especially for sequential authentication implementations

33. 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

34. Utilize authentication for connections to external systems that involve sensitive information or functions

35. 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

36. Use only HTTP POST requests to transmit authentication credentials

37. 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

38. 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)

39. Enforce password length requirements established by policy or regulation. Eight characters is commonly used, but 16 is better or consider the use of multi-word pass phrases

40. Password entry should be obscured on the user's screen. (e.g., on web forms use the input type "password")

41. 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

42. Password reset and changing operations require the same level of controls as account creation and authentication.

43. Password reset questions should support sufficiently random answers. (e.g., "favorite book" is a bad question because “The Bible” is a very common answer)

44. If using email based resets, only send email to a pre-registered address with a temporary link/password

45. Temporary passwords and links should have a short expiration time

46. Enforce the changing of temporary passwords on the next use

47. Notify users when a password reset occurs

48. Prevent password re-use

49. Passwords should be at least one day old before they can be changed, to prevent attacks on password re-use

50. 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

51. Disable "remember me" functionality for password fields

52. The last use (successful or unsuccessful) of a user account should be reported to the user at their next successful login

53. 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

54. Change all vendor-supplied default passwords and user IDs or disable the associated accounts

55. Re-authenticate users prior to performing critical operations

56. Use Multi-Factor Authentication for highly sensitive or high value transactional accounts

57. If using third party code for authentication, inspect the code carefully to ensure it is not affected by any malicious code

Session Management

58. Use the server or framework’s session management controls. The application should only recognize these session identifiers as valid

59. Session identifier creation must always be done on a trusted system (e.g., The server)

60. Session management controls should use well vetted algorithms that ensure sufficiently random session identifiers

61. Set the domain and path for cookies containing authenticated session identifiers to an appropriately restricted value for the site

62. Logout functionality should fully terminate the associated session or connection

63. Logout functionality should be available from all pages protected by authorization

64. 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

65. 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

66. If a session was established before login, close that session and establish a new session after a successful login

67. Generate a new session identifier on any re-authentication

68. Do not allow concurrent logins with the same user ID

69. 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

70. Protect server side session data from unauthorized access, by other users of the server, by implementing appropriate access controls on the server

71. Generate a new session identifier and deactivate the old one periodically. (This can mitigate certain session hijacking scenarios where the original identifier was compromised)

72. 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.

73. 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

74. Supplement standard session management for highly sensitive or critical operations by utilizing per-request, as opposed to per-session, strong random tokens or parameters

75. Set the "secure" attribute for cookies transmitted over an TLS connection

76. 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

77. Use only trusted system objects, e.g. server side session objects, for making access authorization decisions

78. Use a single site-wide component to check access authorization. This includes libraries that call external authorization services

79. Access controls should fail securely

80. Deny all access if the application cannot access its security configuration information

81. 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

82. Segregate privileged logic from other application code

83. Restrict access to files or other resources, including those outside the application's direct control, to only authorized users

84. Restrict access to protected URLs to only authorized users

85. Restrict access to protected functions to only authorized users

86. Restrict direct object references to only authorized users

87. Restrict access to services to only authorized users

88. Restrict access to application data to only authorized users

89. Restrict access to user and data attributes and policy information used by access controls

90. Restrict access security-relevant configuration information to only authorized users

91. Server side implementation and presentation layer representations of access control rules must match

92. If state data must be stored on the client, use encryption and integrity checking on the server side to catch state tampering.

93. Enforce application logic flows to comply with business rules

94. 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

95. Use the "referer" header as a supplemental check only, it should never be the sole authorization check, as it is can be spoofed

96. 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

97. 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.)

98. The application must support disabling of accounts and terminating sessions when authorization ceases (e.g., Changes to role, employment status, business process, etc.)

99. Service accounts or accounts supporting connections to or from external systems should have the least privilege possible

100. 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

101. All cryptographic functions used to protect secrets from the application user must be implemented on a trusted system (e.g., The server)

102. Protect master secrets from unauthorized access

103. Cryptographic modules should fail securely

104. 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

105. 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)

106. Establish and utilize a policy and process for how cryptographic keys will be managed

Error Handling and Logging

107. Do not disclose sensitive information in error responses, including system details, session identifiers or account information

108. Use error handlers that do not display debugging or stack trace information

109. Implement generic error messages and use custom error pages

110. The application should handle application errors and not rely on the server configuration

111. Properly free allocated memory when error conditions occur

112. Error handling logic associated with security controls should deny access by default

113. All logging controls should be implemented on a trusted system (e.g., The server)

114. Logging controls should support both success and failure of specified security events

115. Ensure logs contain important log event data

116. Ensure log entries that include un-trusted data will not execute as code in the intended log viewing interface or software

117. Restrict access to logs to only authorized individuals

118. Utilize a master routine for all logging operations

119. Do not store sensitive information in logs, including unnecessary system details, session identifiers or passwords

120. Ensure that a mechanism exists to conduct log analysis

121. Log all input validation failures

122. Log all authentication attempts, especially failures

123. Log all access control failures

124. Log all apparent tampering events, including unexpected changes to state data

125. Log attempts to connect with invalid or expired session tokens

126. Log all system exceptions

127. Log all administrative functions, including changes to the security configuration settings

128. Log all backend TLS connection failures

129. Log cryptographic module failures

130. Use a cryptographic hash function to validate log entry integrity Data Protection:

131. Implement least privilege, restrict users to only the functionality, data and system information that is required to perform their tasks

132. 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.

133. 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

134. Protect server-side source-code from being downloaded by a user

135. 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

136. Remove comments in user accessible production code that may reveal backend system or other sensitive information

137. Remove unnecessary application and system documentation as this can reveal useful information to attackers

138. Do not include sensitive information in HTTP GET request parameters

139. Disable auto complete features on forms expected to contain sensitive information, including authentication

140. 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

141. The application should support the removal of sensitive data when that data is no longer required. (e.g. personal information or certain financial data)

142. 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

143. 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

144. TLS certificates should be valid and have the correct domain name, not be expired, and be installed with intermediate certificates when required

145. Failed TLS connections should not fall back to an insecure connection

146. Utilize TLS connections for all content requiring authenticated access and for all other sensitive information

147. Utilize TLS for connections to external systems that involve sensitive information or functions

148. Utilize a single standard TLS implementation that is configured appropriately

149. Specify character encodings for all connections

150. Filter parameters containing sensitive information from the HTTP referer, when linking to external sites

System Configuration

151. Ensure servers, frameworks and system components are running the latest approved version

152. Ensure servers, frameworks and system components have all patches issued for the version in use

153. Turn off directory listings

154. Restrict the web server, process and service accounts to the least privileges possible

155. When exceptions occur, fail securely

156. Remove all unnecessary functionality and files

157. Remove test code or any functionality not intended for production, prior to deployment

158. 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

159. Define which HTTP methods, Get or Post, the application will support and whether it will be handled differently in different pages in the application

160. 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

161. 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)

162. Remove unnecessary information from HTTP response headers related to the OS, web-server version and application frameworks

163. The security configuration store for the application should be able to be output in human readable form to support auditing

164. Implement an asset management system and register system components and software in it

165. 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

166. Implement a software change control system to manage and record changes to the code both in development and production

Database Security

167. Use strongly typed parameterized queries

168. Utilize input validation and output encoding and be sure to address meta characters. If these fail, do not run the database command

169. Ensure that variables are strongly typed

170. The application should use the lowest possible level of privilege when accessing the database

171. Use secure credentials for database access

172. 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.

173. Use stored procedures to abstract data access and allow for the removal of permissions to the base tables in the database

174. Close the connection as soon as possible

175. Remove or change all default database administrative passwords. Utilize strong passwords/phrases or implement multi-factor authentication

176. 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))

177. Remove unnecessary default vendor content (e.g., sample schemas)

178. Disable any default accounts that are not required to support business requirements

179. The application should connect to the database with different credentials for every trust distinction (e.g., user, read-only user, guest, administrators)

File Management

180. Do not pass user supplied data directly to any dynamic include function

181. Require authentication before allowing a file to be uploaded

182. Limit the type of files that can be uploaded to only those types that are needed for business purposes

183. Validate uploaded files are the expected type by checking file headers. Checking for file type by extension alone is not sufficient

184. Do not save files in the same web context as the application. Files should either go to the content server or in the database.

185. Prevent or restrict the uploading of any file that may be interpreted by the web server.

186. Turn off execution privileges on file upload directories

187. Implement safe uploading in UNIX by mounting the targeted file directory as a logical drive using the associated path or the chrooted environment

188. 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

189. 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

190. Do not pass directory or file paths, use index values mapped to pre-defined list of paths

191. Never send the absolute file path to the client

192. Ensure application files and resources are read-only

193. Scan user uploaded files for viruses and malware

Memory Management

194. Utilize input and output control for un-trusted data

195. Double check that the buffer is as large as specified

196. 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

197. Check buffer boundaries if calling the function in a loop and make sure there is no danger of writing past the allocated space

198. Truncate all input strings to a reasonable length before passing them to the copy and concatenation functions

199. Specifically close resources, don’t rely on garbage collection. (e.g., connection objects, file handles, etc.)

200. Use non-executable stacks when available

201. Avoid the use of known vulnerable functions (e.g., printf, strcat, strcpy etc.)

202. Properly free allocated memory upon the completion of functions and at all exit points

General Coding Practices

203. Use tested and approved managed code rather than creating new unmanaged code for common tasks

204. 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

205. Use checksums or hashes to verify the integrity of interpreted code, libraries, executables, and configuration files

206. Utilize locking to prevent multiple simultaneous requests or use a synchronization mechanism to prevent race conditions

207. Protect shared variables and resources from inappropriate concurrent access

208. Explicitly initialize all your variables and other data stores, either during declaration or just before the first usage

209. In cases where the application must run with elevated privileges, raise privileges as late as possible, and drop them as soon as possible

210. 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

211. Do not pass user supplied data to any dynamic execution function

212. Restrict users from generating new code or altering existing code

213. Review all secondary applications, third party code and libraries to determine business necessity and validate safe functionality, as these can introduce new vulnerabilities

214. 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