CWE-20: Improper Input Validation

CWE-20: Improper Input Validation is a Common Weakness Enumeration (CWE) entry maintained by MITRE. 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.

Yes. CWE-20 ranked #9 in the CWE Top 25 for 2024, associated with 2,318 CVEs that year. The CWE Top 25 highlights the most common and impactful software weaknesses based on real-world vulnerability data.

If exploited, CWE-20 (Improper Input Validation) it can compromise Availability, Confidentiality and Integrity, leading to outcomes such as DoS: Crash, Exit, or Restart, DoS: Resource Consumption (CPU), DoS: Resource Consumption (Memory), Read Memory, Read Files or Directories and Modify Memory.

Recommended mitigations for CWE-20 include: 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] 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. 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.

CWE-20 can be detected using Dynamic Analysis with Automated Results Interpretation, Dynamic Analysis with Manual Results Interpretation, Manual Static Analysis - Source Code, Automated Static Analysis - Source Code and Architecture or Design Review. Combining automated tooling with manual review typically yields the best coverage.

CWE-20 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

MITRE documents real CVEs mapped to CWE-20, including CVE-2024-37032, CVE-2022-45918, CVE-2021-30860, CVE-2021-30663 and CVE-2021-22205. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.

A CWE (Common Weakness Enumeration) like CWE-20 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.