CWE-665: Improper Initialization

What is CWE-665?

The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used.

This can have security implications when the associated resource is expected to have certain properties or values, such as a variable that determines whether a user has been authenticated or not.

CWE-665 is a class-level weakness in MITRE’s Common Weakness Enumeration, with a MITRE likelihood of exploit of Medium. Applicable platforms: Not Language-Specific.

Source: MITRE CWE (CWE-665 definition, reproduced verbatim). Counts and linkage below are Threadlinqs data.

Consequences

Confidentiality — Read Memory, Read Application Data. When reusing a resource such as memory or a program variable, the original contents of that resource may not be cleared before it is sent to an untrusted party.
Access Control — Bypass Protection Mechanism. If security-critical decisions rely on a variable having a "0" or equivalent value, and the programming language performs this initialization on behalf of the programmer, then a bypass of security may occur.
Availability — DoS: Crash, Exit, or Restart. The uninitialized data may contain values that cause program flow to change in ways that the programmer did not intend. For example, if an uninitialized variable is used as an array index in C, then its previous contents may produce an index that is outside the range of the array, possibly causing a crash or an exit in other environments.

Source: MITRE CWE, common consequences.

How CWE-665 is exploited in the wild

Threadlinqs maps 3 CVEs to CWE-665, published between 2020-12-08 and 2026-07-16. 2 are listed in CISA’s Known Exploited Vulnerabilities catalog, the authoritative record of exploitation in the wild. By CVSS v3 severity the set splits into 1 high, 2 medium. The highest EPSS score in the set is 92.7% (CVE-2022-0847), the modelled probability of exploitation in the next 30 days. 15 tracked threats reference CWE-665 directly or through a CVE it covers; the most recent is “AI-Agent-Driven Intrusion Campaign: Captured Attacker Logs Show Claude opus-4.5 and Codex gpt-5.2-codex Used to Breach 14+ Companies (Livewire CVE-2025-54068, CitrixBleed 2 CVE-2025-5777, Squid, Ghostscript, PwnKit, Dirty Pipe)” (2026-10-30). Affected products concentrate in Apple (1), h2o (1).

Vulnerabilities (CVEs)

All 3 CVEs mapped to CWE-665, CISA KEV first, then by CVSS score.

CVE-2022-0847 — CISA KEV · CVSS 7.8 high · EPSS 92.7% · published 2022-03-07
CVE-2020-27950 — CISA KEV · CVSS 5.5 medium · EPSS 16.5% · published 2020-12-08
CVE-2026-44434 — CVSS 5.3 medium · published 2026-07-16

Affected vendors

Apple — 1 CVE
h2o — 1 CVE

Threat activity

15 tracked threats cite CWE-665:

Mitigations

Requirements / Language Selection: Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, in Java, if the programmer does not explicitly initialize a variable, then the code could produce a compile-time error (if the variable is local) or automatically initialize the variable to the default value for the variable's type. In Perl, if explicit initialization is not performed, then a default value of undef is assigned, which is interpreted as 0, false, or an equivalent value depending on the context in which the variable is accessed.
Architecture and Design: Identify all variables and data stores that receive information from external sources, and apply input validation to make sure that they are only initialized to expected values.
Implementation: Explicitly initialize all your variables and other data stores, either during declaration or just before the first usage.
Implementation: Pay close attention to complex conditionals that affect initialization, since some conditions might not perform the initialization.
Implementation: Avoid race conditions (CWE-362) during initialization routines.
Build and Compilation: Run or compile your product with settings that generate warnings about uninitialized variables or data.

Source: MITRE CWE, potential mitigations.

Detection methods (MITRE CWE)

Automated Dynamic Analysis: This weakness can be detected using 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. Initialization problems may be detected with a stress-test by calling the software simultaneously from a large number of threads or processes, and look for evidence…
Manual Dynamic Analysis: Identify error conditions that are not likely to occur during normal usage and trigger them. For example, run the program under low memory conditions, run with insufficient privileges or permissions, interrupt a transaction before it is completed, or disable connectivity to basic network services such as DNS. Monitor the software for any unexpected behavior. If you trigger an unhandled exception or similar error that was discovered and handled by the application's environment, it may still…
Automated Static Analysis: Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Source: MITRE CWE, detection methods. Threadlinqs detection rules for the threats above are Blue tier and higher.

Related weaknesses

CWE-664