Improper Input ValidationID: 20 | Date: (C)2012-05-14 (M)2022-10-10 | Type: weakness | Status: USABLE | Abstraction Type: Class |
Description The product does not validate or incorrectly validates input
that can affect the control flow or data flow of a
program. Extended DescriptionWhen software does not validate input properly, an attacker is able to
craft the input in a form that is not expected by the rest of the
application. This will lead to parts of the system receiving unintended
input, which may result in altered control flow, arbitrary control of a
resource, or arbitrary code execution. Likelihood of Exploit: High Applicable PlatformsLanguage Class: Language-independent Time Of Introduction - Architecture and Design
- Implementation
Related Attack Patterns Common Consequences Scope | Technical Impact | Notes |
---|
Availability | DoS: crash / exit /
restartDoS: resource consumption
(CPU)DoS: resource consumption
(memory) | An attacker could provide unexpected values and cause a program crash
or excessive consumption of resources, such as memory and CPU. | Confidentiality | Read memoryRead files or
directories | An attacker could read confidential data if they are able to control
resource references. | IntegrityConfidentialityAvailability | Modify memoryExecute unauthorized code or
commands | An attacker could use malicious input to modify data or possibly alter
control flow in unexpected ways, including arbitrary command
execution. |
Detection Methods Name | Description | Effectiveness | Notes |
---|
Automated Static Analysis | Some instances of improper input validation can be detected using
automated static analysis.A static analysis tool might allow the user to specify which
application-specific methods or functions perform input validation; the
tool might also have built-in knowledge of validation frameworks such as
Struts. The tool may then suppress or de-prioritize any associated
warnings. This allows the analyst to focus on areas of the software in
which input validation does not appear to be present.Except in the cases described in the previous paragraph, automated
static analysis might not be able to recognize when proper input
validation is being performed, leading to false positives - i.e.,
warnings that do not have any security consequences or require any code
changes. | | | Manual Static Analysis | When custom input validation is required, such as when enforcing
business rules, manual analysis is necessary to ensure that the
validation is properly implemented. | | | Fuzzing | Fuzzing techniques can be useful for detecting input validation
errors. When unexpected inputs are provided to the software, the
software should not crash or otherwise become unstable, and it should
generate application-controlled error messages. If exceptions or
interpreter-generated error messages occur, this indicates that the
input was not detected and handled within the application logic
itself. | | |
Potential Mitigations Phase | Strategy | Description | Effectiveness | Notes |
---|
Architecture and Design | Input ValidationLibraries or Frameworks | Use an input validation framework such as Struts or the OWASP ESAPI
Validation API. If you use Struts, be mindful of weaknesses covered by
the CWE-101 category. | | | Architecture and DesignImplementation | Identify and Reduce Attack Surface | Understand all the potential areas where untrusted inputs can enter
your software: parameters or arguments, cookies, anything read from the
network, environment variables, reverse DNS lookups, query results,
request headers, URL components, e-mail, files, filenames, databases,
and any external systems that provide data to the application. Remember
that such inputs may be obtained indirectly through API calls. | | | Implementation | Input Validation | Assume all input is malicious. Use an "accept known good" input
validation strategy, i.e., use a whitelist of acceptable inputs that
strictly conform to specifications. Reject any input that does not
strictly conform to specifications, or transform it into something that
does.When performing input validation, consider all potentially relevant
properties, including length, type of input, the full range of
acceptable values, missing or extra inputs, syntax, consistency across
related fields, and conformance to business rules. As an example of
business rule logic, "boat" may be syntactically valid because it only
contains alphanumeric characters, but it is not valid if the input is
only expected to contain colors such as "red" or "blue."Do not rely exclusively on looking for malicious or malformed inputs
(i.e., do not rely on a blacklist). A blacklist is likely to miss at
least one undesirable input, especially if the code's environment
changes. This can give attackers enough room to bypass the intended
validation. However, blacklists can be useful for detecting potential
attacks or determining which inputs are so malformed that they should be
rejected outright. | | | 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.Even though client-side checks provide minimal benefits with respect
to server-side security, they are still useful. First, they can support
intrusion detection. If the server receives input that should have been
rejected by the client, then it may be an indication of an attack.
Second, client-side error-checking can provide helpful feedback to the
user about the expectations for valid input. Third, there may be a
reduction in server-side processing time for accidental input errors,
although this is typically a small savings. | | | Implementation | | When your application combines data from multiple sources, perform the
validation after the sources have been combined. The individual data
elements may pass the validation step but violate the intended
restrictions after they have been combined. | | | Implementation | | Be especially careful to validate all input when invoking code that
crosses language boundaries, such as from an interpreted language to
native code. This could create an unexpected interaction between the
language boundaries. Ensure that you are not violating any of the
expectations of the language with which you are interfacing. For
example, even though Java may not be susceptible to buffer overflows,
providing a large argument in a call to native code might trigger an
overflow. | | | Implementation | | Directly convert your input type into the expected data type, such as
using a conversion function that translates a string into a number.
After converting to the expected data type, ensure that the input's
values fall within the expected range of allowable values and that
multi-field consistencies are maintained. | | | Implementation | | Inputs should be decoded and canonicalized to the application's
current internal representation before being validated (CWE-180,
CWE-181). Make sure that your application does not inadvertently decode
the same input twice (CWE-174). Such errors could be used to bypass
whitelist schemes by introducing dangerous inputs after they have been
checked. Use libraries such as the OWASP ESAPI Canonicalization
control.Consider performing repeated canonicalization until your input does
not change any more. This will avoid double-decoding and similar
scenarios, but it might inadvertently modify inputs that are allowed to
contain properly-encoded dangerous content. | | | 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. | | |
RelationshipsCWE-116 and CWE-20 have a close association because, depending on the
nature of the structured message, proper input validation can indirectly
prevent special characters from changing the meaning of a structured
message. For example, by validating that a numeric ID field should only
contain the 0-9 characters, the programmer effectively prevents injection
attacks.However, input validation is not always sufficient, especially when less
stringent data types must be supported, such as free-form text. Consider a
SQL injection scenario in which a last name is inserted into a query. 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 neutralized. 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. Related CWE | Type | View | Chain |
---|
CWE-20 ChildOf CWE-896 | Category | CWE-888 | |
Demonstrative Examples (Details) - The following example shows a PHP application in which the
programmer attempts to display a user's birthday and homepage.
- The following example takes a user-supplied value to allocate an
array of objects and then operates on the array. (Demonstrative Example Id DX-34)
- This example asks the user for a height and width of an m X n game
board with a maximum dimension of 100 squares.
- This example demonstrates a shopping interaction in which the user
is free to specify the quantity of items to be purchased and a total is
calculated.
- This function attempts to extract a pair of numbers from a
user-supplied string.
Observed Examples - CVE-2008-5305 : Eval injection in Perl program using an ID that should only contain hyphens and numbers.
- CVE-2008-2223 : SQL injection through an ID that was supposed to be numeric.
- CVE-2008-3477 : lack of input validation in spreadsheet program leads to buffer overflows, integer overflows, array index errors, and memory corruption.
- CVE-2008-3843 : insufficient validation enables XSS
- CVE-2008-3174 : driver in security product allows code execution due to insufficient validation
- CVE-2007-3409 : infinite loop from DNS packet with a label that points to itself
- CVE-2006-6870 : infinite loop from DNS packet with a label that points to itself
- CVE-2008-1303 : missing parameter leads to crash
- CVE-2007-5893 : HTTP request with missing protocol version number leads to crash
- CVE-2006-6658 : request with missing parameters leads to information exposure
- CVE-2008-4114 : system crash with offset value that is inconsistent with packet size
- CVE-2006-3790 : size field that is inconsistent with packet size leads to buffer over-read
- CVE-2008-2309 : product uses a blacklist to identify potentially dangerous content, allowing attacker to bypass a warning
- CVE-2008-3494 : security bypass via an extra header
- CVE-2006-5462 : use of extra data in a signature allows certificate signature forging
- CVE-2008-3571 : empty packet triggers reboot
- CVE-2006-5525 : incomplete blacklist allows SQL injection
- CVE-2008-1284 : NUL byte in theme name cause directory traversal impact to be worse
- CVE-2008-0600 : kernel does not validate an incoming pointer before dereferencing it
- CVE-2008-1738 : anti-virus product has insufficient input validation of hooked SSDT functions, allowing code execution
- CVE-2008-1737 : anti-virus product allows DoS via zero-length field
- CVE-2008-3464 : driver does not validate input from userland to the kernel
- CVE-2008-2252 : kernel does not validate parameters sent in from userland, allowing code execution
- CVE-2008-2374 : lack of validation of string length fields allows memory consumption or buffer over-read
- CVE-2008-1440 : lack of validation of length field leads to infinite loop
- CVE-2008-1625 : lack of validation of input to an IOCTL allows code execution
- CVE-2008-3177 : zero-length attachment causes crash
- CVE-2007-2442 : zero-length input causes free of uninitialized pointer
- CVE-2008-5563 : crash via a malformed frame structure
- CVE-2008-5285 : infinite loop from a long SMTP request
- CVE-2008-3812 : router crashes with a malformed packet
- CVE-2008-3680 : packet with invalid version number leads to NULL pointer dereference
- CVE-2008-3660 : crash via multiple "." characters in file extension
For more examples, refer to CVE relations in the bottom box. White Box Definitions None Black Box Definitions None Taxynomy Mappings Taxynomy | Id | Name | Fit |
---|
7 Pernicious Kingdoms | | Input validation and representation | | OWASP Top Ten 2004 | A1 | Unvalidated Input | CWE_More_Specific | CERT C Secure Coding | ERR07-C | Prefer functions that support error checking over equivalent
functions that don't | | CERT C Secure Coding | INT06-C | Use strtol() or a related function to convert a string token
to an integer | | CERT C Secure Coding | MEM10-C | Define and use a pointer validation
function | | CERT C Secure Coding | MSC08-C | Library functions should validate their
parameters | | WASC | 20 | Improper Input Handling | | CERT C++ Secure Coding | INT06-CPP | Use strtol() or a related function to convert a string token
to an integer | | CERT C++ Secure Coding | MEM10-CPP | Define and use a pointer validation
function | | CERT C++ Secure Coding | MSC08-CPP | Functions should validate their parameters | |
References: - Jim Manico .Input Validation with ESAPI - Very Important. 2008-08-15.
- OWASP .OWASP Enterprise Security API (ESAPI) Project.
- Joel Scambray Mike Shema Caleb Sima .Hacking Exposed Web Applications, Second
Edition. McGraw-Hill. Section:'Input Validation Attacks'. 2006-06-05.
- Jeremiah Grossman .Input validation or output filtering, which is
better?. 2007-01-30.
- Kevin Beaver .The importance of input validation. 2006-09-06.
- M. Howard D. LeBlanc .Writing Secure Code 2nd Edition. Microsoft. Section:'Chapter 10, "All Input Is Evil!" Page 341'. Published on 2002.
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