Official definition

The product uses a fixed or controlled search path to find resources, but one or more locations in that path can be under the control of unintended actors.

Although this weakness can occur with any type of resource, it is frequently introduced when a product uses a directory search path to find executables or code libraries, but the path contains a directory that can be modified by an attacker, such as "/tmp" or the current working directory.

In Windows-based systems, when the LoadLibrary or LoadLibraryEx function is called with a DLL name that does not contain a fully qualified path, the function follows a search order that includes two path elements that might be uncontrolled:

the directory from which the program has been loaded
the current working directory

In some cases, the attack can be conducted remotely, such as when SMB or WebDAV network shares are used.

One or more locations in that path could include the Windows drive root or its subdirectories. This often exists in Linux-based code assuming the controlled nature of the root directory (/) or its subdirectories (/etc, etc), or a code that recursively accesses the parent directory. In Windows, the drive root and some of its subdirectories have weak permissions by default, which makes them uncontrolled.

In some Unix-based systems, a PATH might be created that contains an empty element, e.g. by splicing an empty variable into the PATH. This empty element can be interpreted as equivalent to the current working directory, which might be an untrusted search element.

In software package management frameworks (e.g., npm, RubyGems, or PyPi), the framework may identify dependencies on third-party libraries or other packages, then consult a repository that contains the desired package. The framework may search a public repository before a private repository. This could be exploited by attackers by placing a malicious package in the public repository that has the same name as a package from the private repository. The search path might not be directly under control of the developer relying on the framework, but this search order effectively contains an untrusted element.

Characteristics

Alternate terms

DLL preloading — This term is one of several that are used to describe exploitation of untrusted search path elements in Windows systems, which received wide attention in August 2010. From a weakness perspective, the term is imprecise because it can apply to both CWE-426 and CWE-427.
Binary planting — This term is one of several that are used to describe exploitation of untrusted search path elements in Windows systems, which received wide attention in August 2010. From a weakness perspective, the term is imprecise because it can apply to both CWE-426 and CWE-427.
Insecure library loading — This term is one of several that are used to describe exploitation of untrusted search path elements in Windows systems, which received wide attention in August 2010. From a weakness perspective, the term is imprecise because it can apply to both CWE-426 and CWE-427.
Dependency confusion — As of February 2021, this term is used to describe CWE-427 in the context of managing installation of software package dependencies, in which attackers release packages on public sites where the names are the same as package names used by private repositories, and the search for the dependent package tries the public site first, downloading untrusted code. It may also be referred to as a "substitution attack."

Modes of introduction

Implementation

Common consequences

Impact	Scope	Explanation
Execute Unauthorized Code or Commands	Confidentiality, Integrity, Availability	—

Risk mitigations

Attack Surface Reduction · Architecture and Design, ImplementationHard-code the search path to a set of known-safe values (such as system directories), or only allow them to be specified by the administrator in a configuration file. Do not allow these settings to be modified by an external party. Be careful to avoid related weaknesses such as CWE-426 and CWE-428.
Attack Surface Reduction · ImplementationWhen invoking other programs, specify those programs using fully-qualified pathnames. While this is an effective approach, code that uses fully-qualified pathnames might not be portable to other systems that do not use the same pathnames. The portability can be improved by locating the full-qualified paths in a centralized, easily-modifiable location within the source code, and having the code refer to these paths.
Attack Surface Reduction · ImplementationRemove or restrict all environment settings before invoking other programs. This includes the PATH environment variable, LD_LIBRARY_PATH, and other settings that identify the location of code libraries, and any application-specific search paths.
ImplementationCheck your search path before use and remove any elements that are likely to be unsafe, such as the current working directory or a temporary files directory. Since this is a denylist approach, it might not be a complete solution.
ImplementationUse other functions that require explicit paths. Making use of any of the other readily available functions that require explicit paths is a safe way to avoid this problem. For example, system() in C does not require a full path since the shell can take care of finding the program using the PATH environment variable, while execl() and execv() require a full path.

Detection methods

Method	Approach	Effectiveness
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.)	High

Representative vulnerabilities

Below are representative vulnerabilities related to this CWE, prioritized by severity.

Sources (16)

Dynamic-Link Library Security Insecure Library Loading Could Allow Remote Code Execution

CWE-427: Uncontrolled Search Path Element

What is CWE-427?

Data statistics

Vulnerabilities mapped to CWE-427

Vulnerabilities in CISA KEV for CWE-427