CWE-20: Improper Input Validation

Opis

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

Input validation is a frequently-used technique for checking potentially dangerous inputs in order to ensure that the inputs are safe for processing within the code, or when communicating with other components.

Input can consist of:

- raw data - strings, numbers, parameters, file contents, etc.

- metadata - information about the raw data, such as headers or size

Data can be simple or structured. Structured data can be composed of many nested layers, composed of combinations of metadata and raw data, with other simple or structured data.

Many properties of raw data or metadata may need to be validated upon entry into the code, such as:

- specified quantities such as size, length, frequency, price, rate, number of operations, time, etc.

- implied or derived quantities, such as the actual size of a file instead of a specified size

- indexes, offsets, or positions into more complex data structures

- symbolic keys or other elements into hash tables, associative arrays, etc.

- well-formedness, i.e. syntactic correctness - compliance with expected syntax

- lexical token correctness - compliance with rules for what is treated as a token

- specified or derived type - the actual type of the input (or what the input appears to be)

- consistency - between individual data elements, between raw data and metadata, between references, etc.

- conformance to domain-specific rules, e.g. business logic

- equivalence - ensuring that equivalent inputs are treated the same

- authenticity, ownership, or other attestations about the input, e.g. a cryptographic signature to prove the source of the data

Implied or derived properties of data must often be calculated or inferred by the code itself. Errors in deriving properties may be considered a contributing factor to improper input validation.

Skutki

Availability
DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)
An attacker could provide unexpected values and cause a program crash or arbitrary control of resource allocation, leading to excessive consumption of resources such as memory and CPU.
Confidentiality
Read Memory; Read Files or Directories
An attacker could read confidential data if they are able to control resource references.
Integrity, Confidentiality, Availability
Modify Memory; Execute 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.

Zapobieganie

Architecture and Design · Attack Surface Reduction
Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build "recognizers" for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses. [REF-1109] [REF-1110] [REF-1111]
Architecture and Design · Libraries or Frameworks
Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
Architecture and Design, Implementation · Attack Surface Reduction
Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: 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 list 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. This 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, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Skuteczność: High
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 allowlist 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.

Przykłady podatności

CVE-2024-37032 Large language model (LLM) management tool does not validate the format of a digest value (CWE-1287) from a private, untrusted model registry, enabling relative path traversal (CWE-23), a.k.a. Probllama
CVE-2022-45918 Chain: a learning management tool debugger uses external input to locate previous session logs (CWE-73) and does not properly validate the given path (CWE-20), allowing for filesystem path traversal using "../" sequences (CWE-24)
CVE-2021-30860 Chain: improper input validation (CWE-20) leads to integer overflow (CWE-190) in mobile OS, as exploited in the wild per CISA KEV.
CVE-2021-30663 Chain: improper input validation (CWE-20) leads to integer overflow (CWE-190) in mobile OS, as exploited in the wild per CISA KEV.
CVE-2021-22205 Chain: backslash followed by a newline can bypass a validation step (CWE-20), leading to eval injection (CWE-95), as exploited in the wild per CISA KEV.
CVE-2021-21220 Chain: insufficient input validation (CWE-20) in browser allows heap corruption (CWE-787), as exploited in the wild per CISA KEV.
CVE-2020-9054 Chain: improper input validation (CWE-20) in username parameter, leading to OS command injection (CWE-78), as exploited in the wild per CISA KEV.
CVE-2020-3452 Chain: security product has improper input validation (CWE-20) leading to directory traversal (CWE-22), as exploited in the wild per CISA KEV.
CVE-2020-3161 Improper input validation of HTTP requests in IP phone, as exploited in the wild per CISA KEV.
CVE-2020-3580 Chain: improper input validation (CWE-20) in firewall product leads to XSS (CWE-79), as exploited in the wild per CISA KEV.
CVE-2021-37147 Chain: caching proxy server has improper input validation (CWE-20) of headers, allowing HTTP response smuggling (CWE-444) using an "LF line ending"
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 denylist to identify potentially dangerous content, allowing attacker to bypass a warning
CVE-2008-3494 security bypass via an extra header
CVE-2008-3571 empty packet triggers reboot
CVE-2006-5525 incomplete denylist allows SQL injection
CVE-2008-1284 NUL byte in theme name causes 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

Słabość nadrzędna

CWE-707 Improper Neutralization

Pokrewna

CWE-345 Insufficient Verification of Data Authenticity

Może prowadzić do

Słabości podrzędne

Kiedy powstaje

Architecture and Design
Implementation — REALIZATION: This weakness is caused during implementation of an architectural security tactic. If a programmer believes that an attacker cannot modify certain inputs, then the programmer might not perform any input validation at all. For example, in web applications, many programmers believe that cookies and hidden form fields can not be modified from a web browser (CWE-472), although they can be altered using a proxy or a custom program. In a client-server architecture, the programmer might assume that client-side security checks cannot be bypassed, even when a custom client could be written that skips those checks (CWE-602).

Dotyczy

Not Language-Specific, AI/ML

Uwagi

CWE-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.

Multiple techniques exist to transform potentially dangerous input into something safe, which is different than "validation," which is a technique to check if an input is already safe. CWE users need to be cautious during root cause analysis to ensure that an issue is truly an input-validation problem.

As of 2020, this entry is used more often than preferred, and it is a source of frequent confusion. It is being actively modified for CWE 4.1 and subsequent versions.

Concepts such as validation, data transformation, and neutralization are being refined, so relationships between CWE-20 and other entries such as CWE-707 may change in future versions, along with an update to the Vulnerability Theory document.

Input validation - whether missing or incorrect - is such an essential and widespread part of secure development that it is implicit in many different weaknesses. Traditionally, problems such as buffer overflows and XSS have been classified as input validation problems by many security professionals. However, input validation is not necessarily the only protection mechanism available for avoiding such problems, and in some cases it is not even sufficient. The CWE team has begun capturing these subtleties in chains within the Research Concepts view (CWE-1000), but more work is needed.

The "input validation" term is extremely common, but it is used in many different ways. In some cases its usage can obscure the real underlying weakness or otherwise hide chaining and composite relationships.

Some people use "input validation" as a general term that covers many different neutralization techniques for ensuring that input is appropriate, such as filtering, i.e., attempting to remove dangerous inputs (related to CWE-790); encoding/escaping, i.e., attempting to ensure that the input is not misinterpreted when it is included in output to another component (related to CWE-116); or canonicalization, which often indirectly removes otherwise-dangerous inputs. Others use the term in a narrower context to simply mean "checking if an input conforms to expectations without changing it." CWE uses this narrow interpretation.

Note that "input validation" has very different meanings to different people, or within different classification schemes. Caution must be used when referencing this CWE entry or mapping to it. For example, some weaknesses might involve inadvertently giving control to an attacker over an input when they should not be able to provide an input at all, but sometimes this is referred to as input validation.

Finally, it is important to emphasize that the distinctions between input validation and output escaping are often blurred. Developers must be careful to understand the difference, including how input validation is not always sufficient to prevent vulnerabilities, especially when less stringent data types must be supported, such as free-form text. Consider a SQL injection scenario in which a person's 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, this valid name cannot be directly inserted into the database because it contains the "'" apostrophe character, which would need to be escaped or otherwise transformed. In this case, removing the apostrophe might reduce the risk of SQL injection, but it would produce incorrect behavior because the wrong name would be recorded.

Źródła

Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors — Katrina Tsipenyuk, Brian Chess, Gary McGraw, NIST, 2005
Input Validation with ESAPI - Very Important — Jim Manico, 2008
OWASP Enterprise Security API (ESAPI) Project — OWASP
Hacking Exposed Web Applications, Second Edition — Joel Scambray, Mike Shema, Caleb Sima, Input Validation Attacks, McGraw-Hill, 2006
Input validation or output filtering, which is better? — Jeremiah Grossman, 2007
The importance of input validation — Kevin Beaver, 2006
Writing Secure Code — Michael Howard, David LeBlanc, Chapter 10, "All Input Is Evil!" Page 341, Microsoft Press, 2002
LANGSEC: Language-theoretic Security
LangSec: Recognition, Validation, and Compositional Correctness for Real World Security
Curing the Vulnerable Parser: Design Patterns for Secure Input Handling — Sergey Bratus, Lars Hermerschmidt, Sven M. Hallberg, Michael E. Locasto, Falcon D. Momot, Meredith L. Patterson, Anna Shubina, USENIX ;login:, 2017
Supplemental Details - 2022 CWE Top 25 — MITRE, Details of Problematic Mappings, 2022
State-of-the-Art Resources (SOAR) for Software Vulnerability Detection, Test, and Evaluation — Gregory Larsen, E. Kenneth Hong Fong, David A. Wheeler, Rama S. Moorthy, 2014