Improper Encoding or Escaping of Output
Resource: http://cwe.mitre.org/top25/#CWE-116
Computers have a odd habit of carrying out what you say, not what you imply. Inadequate output encoding is the often-ignored sibling to poor input validation, but it is at the root of most injection-primarily based attacks, which are all the rage these days. An attacker can modify the commands that you intend to mail to other components, possibly leading to a total compromise of your application – not to point out exposing the other components to exploits that the attacker would not be in a position to start immediately. This turns “do what I indicate” into “do what the attacker states.” When your system generates outputs to other parts in the sort of structured messages these kinds of as queries or requests, it wants to separate management details and metadata from the real info. This is straightforward to forget, since a lot of paradigms carry info and commands bundled together in the same stream, with only a couple of special characters enforcing the boundaries. An illustration is World wide web 2. and other frameworks that work by blurring these lines. This more exposes them to assault.
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Prevention and Mitigations
Architecture and Design Use languages, libraries, or frameworks that make it less difficult to produce effectively encoded output.
Examples include the ESAPI Encoding manage.
Alternately, use created-in functions, but contemplate employing wrappers in case people functions are found out to have a vulnerability.
Architecture and Layout If accessible, use structured mechanisms that instantly enforce the separation between knowledge and code. These mechanisms may possibly be in a position to supply the related quoting, encoding, and validation automatically, alternatively of relying on the developer to offer this capability at each and every stage exactly where output is produced.
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For instance, saved processes can enforce database query framework and reduce the likelihood of SQL injection.
Architecture and Design Understand the context in which your knowledge will be utilised and the encoding that will be expected. This is specifically crucial when transmitting knowledge among various components, or when creating outputs that can contain several encodings at the very same time, this kind of as net pages or multi-component mail messages. Examine all expected communication protocols and info representations to figure out the necessary encoding techniques.
Architecture and Style In some cases, input validation may be an critical technique when output encoding is not a total remedy. For instance, you may be delivering the exact same output that will be processed by numerous customers that use various encodings or representations. In other cases, you might be required to enable consumer-provided input to have control details, this kind of as limited HTML tags that assistance formatting in a wiki or bulletin board. When this type of requirement ought to be satisfied, use an incredibly rigorous whitelist to limit which manage sequences can be used. Verify that the resulting syntactic construction is what you expect. Use your typical encoding techniques for the remainder of the input.
Architecture and Design and style Use input validation as a defense-in-depth measure to decrease the chance of output encoding errors (see CWE-twenty).
Needs Fully specify which encodings are required by elements that will be communicating with each other.
Implementation When exchanging knowledge among elements, make certain that equally elements are making use of the exact same character encoding. Ensure that the correct encoding is used at every single interface. Explicitly set the encoding you are utilizing every time the protocol allows you to do so.
Testing Use automated static evaluation instruments that target this kind of weakness. Numerous present day techniques use data movement evaluation to decrease the number of fake positives. This is not a excellent answer, since 100% accuracy and coverage are not possible.
Testing Use dynamic instruments and methods that interact with the software package making use of big test suites with a lot of diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software’s operation may possibly sluggish down, but it need to not turn into unstable, crash, or make incorrect results.
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Relevant CWEs
CWE-74 Injection
CWE-78 OS command injection
CWE-79 Cross-web site Scripting (XSS)
CWE-88 Argument Injection
CWE-89 SQL injection
CWE-93 CRLF Injection
Relevant Attack Designs
CAPEC-IDs: [view all]
eighteen, 63, 73, 81, 85, 86, 104
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CWE-89: Incorrect Sanitization of Unique Factors utilised in an SQL Command (‘SQL Injection’)
Summary
Weakness Prevalence Higher Penalties Data loss
Protection bypass
Remediation Cost Lower Ease of Detection Easy
Attack Frequency Typically Attacker Awareness Higher
Discussion
These days, it seems as if computer software is all about the information: obtaining it into the database, pulling it from the database, massaging it into info, and sending it elsewhere for exciting and profit. If attackers can impact the SQL that you use to talk with your database, then they can do nasty points exactly where they get all the enjoyable and revenue. If you use SQL queries in protection controls this sort of as authentication, attackers could alter the logic of those queries to bypass security. They could modify the queries to steal, corrupt, or or else adjust your underlying knowledge. They’re going to even steal information 1 byte at a time if they have to, and they have the patience and know-how to do so.
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Prevention and Mitigations
Architecture and Design and style Use languages, libraries, or frameworks that make it easier to produce appropriately encoded output.
For instance, take into account utilizing persistence layers such as Hibernate or Enterprise Java Beans, which can provide substantial defense against SQL injection if utilized properly.
Architecture and Design If offered, use structured mechanisms that routinely enforce the separation among info and code. These mechanisms may possibly be ready to present the pertinent quoting, encoding, and validation routinely, instead of relying on the developer to offer this ability at each point in which output is produced.
Procedure SQL queries utilizing ready statements, parameterized queries, or stored processes. These attributes should accept parameters or variables and assistance strong typing. Do not dynamically construct and execute query strings inside these features employing “exec” or equivalent features, because you might re-introduce the possibility of SQL injection.
Architecture and Design Adhere to the principle of minimum privilege when producing consumer accounts to a SQL database. The database consumers should only have the minimal privileges required to use their account. If the specifications of the system indicate that a person can examine and modify their own knowledge, then limit their privileges so they can not examine/create others’ info. Use the strictest permissions doable on all database objects, such as execute-only for stored procedures.
Architecture and Design For any security checks that are done on the client facet, ensure that these checks are duplicated on the server facet, in order to steer clear of CWE-602. Attackers can bypass the customer-aspect checks by modifying values following the checks have been done, or by changing the customer to take away the customer-side checks entirely. Then, these modified values would be submitted to the server.
Implementation If you will need to use dynamically-created query strings in spite of the risk, use proper encoding and escaping of inputs. Rather of constructing your individual implementation, this kind of functions could be offered in the database or programming language. For illustration, the Oracle DBMS_ASSERT deal can check out or enforce that parameters have specified properties that make them a lot less susceptible to SQL injection. For MySQL, the mysql_genuine_escape_string() API operate is accessible in equally C and PHP.
Implementation Presume all input is malicious. Use an “accept identified excellent” input validation method (i.e., use a whitelist). Reject any input that does not strictly conform to specs, or rework it into something that does. Use a blacklist to reject any unpredicted inputs and detect prospective attacks.
Use a regular input validation mechanism to validate all input for length, sort, syntax, and business policies before accepting the input for even more processing. As an case in point of enterprise rule logic, “boat” may be syntactically valid because it only consists of alphanumeric characters, but it is not legitimate if you are expecting hues such as “red” or “blue.”
When constructing SQL query strings, use stringent whitelists that restrict the character set based on the anticipated appeal of the parameter in the request. This will indirectly restrict the scope of an assault, but this technique is significantly less crucial than appropriate output encoding and escaping.
Be aware that proper output encoding, escaping, and quoting is the most powerful remedy for stopping SQL injection, despite the fact that input validation could offer some defense-in-depth. This is due to the fact it successfully limits what will look in output. Input validation will not always prevent SQL injection, specifically if you are required to help free-type text fields that could include arbitrary characters. For case in point, the title “O’Reilly” would most likely pass the validation stage, given that it is a common final name in the English language. Nevertheless, it can’t be right inserted into the database because it contains the “‘” apostrophe character, which would require to be escaped or in any other case dealt with. In this case, stripping the apostrophe might lessen the threat of SQL injection, but it would make incorrect conduct due to the fact the incorrect identify would be recorded.
When possible, it could be most secure to disallow meta-characters totally, as an alternative of escaping them. This will present some defense in depth. Right after the knowledge is entered into the database, later on processes might neglect to escape meta-characters prior to use, and you may possibly not have manage over people processes.
Testing Use automated static analysis tools that target this sort of weakness. Many contemporary techniques use data flow analysis to decrease the range of fake positives. This is not a perfect remedy, since one hundred% accuracy and coverage are not feasible.
Testing Use dynamic tools and methods that interact with the software program making use of big check suites with many diverse inputs, these kinds of as fuzz testing (fuzzing), robustness testing, and fault injection. The software’s operation may possibly sluggish down, but it really should not turn into unstable, crash, or create incorrect final results.
Operation Use an software firewall that can detect attacks versus this weakness. This may well not catch all attacks, and it may well call for some effort for customization. Even so, it can be beneficial in circumstances in which the code cannot be fixed (because it is managed by a third celebration), as an emergency prevention measure while a lot more extensive software program assurance actions are used, or to supply defense in depth.
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