Improper Encoding or Escaping of Output

Resource: http://cwe.mitre.org/top25/#CWE-116

Computers have a strange habit of doing what you say, not what you mean. Insufficient output encoding is the often-ignored sibling to poor input validation, but it is at the root of most injection-based attacks, which are all the rage these days. An attacker can modify the commands that you intend to send to other components, possibly leading to a complete compromise of your application - not to mention exposing the other components to exploits that the attacker would not be able to launch directly. This turns "do what I mean" into "do what the attacker says." When your program generates outputs to other components in the form of structured messages such as queries or requests, it needs to separate control information and metadata from the actual data. This is easy to forget, because many paradigms carry data and commands bundled together in the same stream, with only a few special characters enforcing the boundaries. An example is Web 2.0 and other frameworks that work by blurring these lines. This further exposes them to attack.

...View Full Technical Details
Prevention and Mitigations
Architecture and Design Use languages, libraries, or frameworks that make it easier to generate properly encoded output.
Examples include the ESAPI Encoding control.
Alternately, use built-in functions, but consider using wrappers in case those functions are discovered to have a vulnerability.
Architecture and Design If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.

Your Ad Here

For example, stored procedures can enforce database query structure and reduce the likelihood of SQL injection.
Architecture and Design Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies.
Architecture and Design In some cases, input validation may be an important strategy when output encoding is not a complete solution. For example, you may be providing the same output that will be processed by multiple consumers that use different encodings or representations. In other cases, you may be required to allow user-supplied input to contain control information, such as limited HTML tags that support formatting in a wiki or bulletin board. When this type of requirement must be met, use an extremely strict whitelist to limit which control sequences can be used. Verify that the resulting syntactic structure is what you expect. Use your normal encoding methods for the remainder of the input.
Architecture and Design Use input validation as a defense-in-depth measure to reduce the likelihood of output encoding errors (see CWE-20).
Requirements Fully specify which encodings are required by components that will be communicating with each other.
Implementation When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.
Testing Use automated static analysis tools that target this type of weakness. Many modern techniques use data flow analysis to minimize the number of false positives. This is not a perfect solution, since 100% accuracy and coverage are not feasible.
Testing Use dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Your Ad Here

Related CWEs
CWE-74 Injection
CWE-78 OS command injection
CWE-79 Cross-site Scripting (XSS)
CWE-88 Argument Injection
CWE-89 SQL injection
CWE-93 CRLF Injection
Related Attack Patterns

CAPEC-IDs: [view all]
18, 63, 73, 81, 85, 86, 104
Back to top
CWE-89: Improper Sanitization of Special Elements used in an SQL Command ('SQL Injection')
Summary
Weakness Prevalence High Consequences Data loss
Security bypass
Remediation Cost Low Ease of Detection Easy
Attack Frequency Often Attacker Awareness High
Discussion

These days, it seems as if software is all about the data: getting it into the database, pulling it from the database, massaging it into information, and sending it elsewhere for fun and profit. If attackers can influence the SQL that you use to communicate with your database, then they can do nasty things where they get all the fun and profit. If you use SQL queries in security controls such as authentication, attackers could alter the logic of those queries to bypass security. They could modify the queries to steal, corrupt, or otherwise change your underlying data. They'll even steal data one byte at a time if they have to, and they have the patience and know-how to do so.

Your Ad Here

...View Full Technical Details
Prevention and Mitigations
Architecture and Design Use languages, libraries, or frameworks that make it easier to generate properly encoded output.
For example, consider using persistence layers such as Hibernate or Enterprise Java Beans, which can provide significant protection against SQL injection if used properly.
Architecture and Design If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.
Process SQL queries using prepared statements, parameterized queries, or stored procedures. These features should accept parameters or variables and support strong typing. Do not dynamically construct and execute query strings within these features using "exec" or similar functionality, since you may re-introduce the possibility of SQL injection.
Architecture and Design Follow the principle of least privilege when creating user accounts to a SQL database. The database users should only have the minimum privileges necessary to use their account. If the requirements of the system indicate that a user can read and modify their own data, then limit their privileges so they cannot read/write others' data. Use the strictest permissions possible on all database objects, such as execute-only for stored procedures.
Architecture and Design For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Implementation If you need to use dynamically-generated query strings in spite of the risk, use proper encoding and escaping of inputs. Instead of building your own implementation, such features may be available in the database or programming language. For example, the Oracle DBMS_ASSERT package can check or enforce that parameters have certain properties that make them less vulnerable to SQL injection. For MySQL, the mysql_real_escape_string() API function is available in both C and PHP.
Implementation Assume all input is malicious. Use an "accept known good" input validation strategy (i.e., use a whitelist). Reject any input that does not strictly conform to specifications, or transform it into something that does. Use a blacklist to reject any unexpected inputs and detect potential attacks.
Use a standard input validation mechanism to validate all input for length, type, syntax, and business rules before accepting the input for further processing. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if you are expecting colors such as "red" or "blue."
When constructing SQL query strings, use stringent whitelists that limit the character set based on the expected value of the parameter in the request. This will indirectly limit the scope of an attack, but this technique is less important than proper output encoding and escaping.
Note that proper output encoding, escaping, and quoting is the most effective solution for preventing SQL injection, although input validation may provide some defense-in-depth. This is because it effectively limits what will appear in output. Input validation will not always prevent SQL injection, especially if you are required to support free-form text fields that could contain arbitrary characters. For example, the name "O'Reilly" would likely pass the validation step, since it is a common last name in the English language. However, it cannot be directly inserted into the database because it contains the "'" apostrophe character, which would need to be escaped or otherwise handled. In this case, stripping the apostrophe might reduce the risk of SQL injection, but it would produce incorrect behavior because the wrong name would be recorded.
When feasible, it may be safest to disallow meta-characters entirely, instead of escaping them. This will provide some defense in depth. After the data is entered into the database, later processes may neglect to escape meta-characters before use, and you may not have control over those processes.
Testing Use automated static analysis tools that target this type of weakness. Many modern techniques use data flow analysis to minimize the number of false positives. This is not a perfect solution, since 100% accuracy and coverage are not feasible.
Testing Use dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.
Operation Use an application firewall that can detect attacks against this weakness. This might not catch all attacks, and it might require some effort for customization. However, it can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.

Your Ad Here