CWE-470: Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')
Weakness ID: 470
Vulnerability Mapping:
ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities Abstraction: BaseBase - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
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Description
The product uses external input with reflection to select which classes or code to use, but it does not sufficiently prevent the input from selecting improper classes or code.
Extended Description
If the product uses external inputs to determine which class to instantiate or which method to invoke, then an attacker could supply values to select unexpected classes or methods. If this occurs, then the attacker could create control flow paths that were not intended by the developer. These paths could bypass authentication or access control checks, or otherwise cause the product to behave in an unexpected manner. This situation becomes a doomsday scenario if the attacker can upload files into a location that appears on the product's classpath (CWE-427) or add new entries to the product's classpath (CWE-426). Under either of these conditions, the attacker can use reflection to introduce new, malicious behavior into the product.
Alternate Terms
Reflection Injection
Common Consequences
This table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Scope
Impact
Likelihood
Integrity Confidentiality Availability Other
Technical Impact: Execute Unauthorized Code or Commands; Alter Execution Logic
The attacker might be able to execute code that is not directly accessible to the attacker. Alternately, the attacker could call unexpected code in the wrong place or the wrong time, possibly modifying critical system state.
Availability Other
Technical Impact: DoS: Crash, Exit, or Restart; Other
The attacker might be able to use reflection to call the wrong code, possibly with unexpected arguments that violate the API (CWE-227). This could cause the product to exit or hang.
Confidentiality
Technical Impact: Read Application Data
By causing the wrong code to be invoked, the attacker might be able to trigger a runtime error that leaks sensitive information in the error message, such as CWE-536.
Potential Mitigations
Phase: Architecture and Design
Refactor your code to avoid using reflection.
Phase: Architecture and Design
Do not use user-controlled inputs to select and load classes or code.
Phase: Implementation
Apply strict input validation by using allowlists or indirect selection to ensure that the user is only selecting allowable classes or code.
Relationships
This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
Relevant to the view "Research Concepts" (CWE-1000)
Nature
Type
ID
Name
ChildOf
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
Relevant to the view "Software Development" (CWE-699)
Nature
Type
ID
Name
MemberOf
Category - a CWE entry that contains a set of other entries that share a common characteristic.
This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
Nature
Type
ID
Name
ChildOf
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
Relevant to the view "Seven Pernicious Kingdoms" (CWE-700)
Nature
Type
ID
Name
ChildOf
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
Phase
Note
Architecture and Design
Implementation
Applicable Platforms
This listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.
Languages
Java (Undetermined Prevalence)
PHP (Undetermined Prevalence)
Class: Interpreted (Sometimes Prevalent)
Demonstrative Examples
Example 1
A common reason that programmers use the reflection API is to implement their own command dispatcher. The following example shows a command dispatcher that does not use reflection:
(good code)
Example Language: Java
String ctl = request.getParameter("ctl"); Worker ao = null; if (ctl.equals("Add")) {
ao = new AddCommand();
} else if (ctl.equals("Modify")) {
ao = new ModifyCommand();
} else {
throw new UnknownActionError();
} ao.doAction(request);
A programmer might refactor this code to use reflection as follows:
(bad code)
Example Language: Java
String ctl = request.getParameter("ctl"); Class cmdClass = Class.forName(ctl + "Command"); Worker ao = (Worker) cmdClass.newInstance(); ao.doAction(request);
The refactoring initially appears to offer a number of advantages. There are fewer lines of code, the if/else blocks have been entirely eliminated, and it is now possible to add new command types without modifying the command dispatcher. However, the refactoring allows an attacker to instantiate any object that implements the Worker interface. If the command dispatcher is still responsible for access control, then whenever programmers create a new class that implements the Worker interface, they must remember to modify the dispatcher's access control code. If they do not modify the access control code, then some Worker classes will not have any access control.
One way to address this access control problem is to make the Worker object responsible for performing the access control check. An example of the re-refactored code follows:
(bad code)
Example Language: Java
String ctl = request.getParameter("ctl"); Class cmdClass = Class.forName(ctl + "Command"); Worker ao = (Worker) cmdClass.newInstance(); ao.checkAccessControl(request); ao.doAction(request);
Although this is an improvement, it encourages a decentralized approach to access control, which makes it easier for programmers to make access control mistakes. This code also highlights another security problem with using reflection to build a command dispatcher. An attacker can invoke the default constructor for any kind of object. In fact, the attacker is not even constrained to objects that implement the Worker interface; the default constructor for any object in the system can be invoked. If the object does not implement the Worker interface, a ClassCastException will be thrown before the assignment to ao, but if the constructor performs operations that work in the attacker's favor, the damage will already have been done. Although this scenario is relatively benign in simple products, in larger products where complexity grows exponentially it is not unreasonable that an attacker could find a constructor to leverage as part of an attack.
Database system allows attackers to bypass sandbox restrictions by using the Reflection API.
Detection Methods
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.)
Effectiveness: High
Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
Nature
Type
ID
Name
MemberOf
Category - a CWE entry that contains a set of other entries that share a common characteristic.
View - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).
(this CWE ID could be used to map to real-world vulnerabilities)
Reason: Acceptable-Use
Rationale:
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comments:
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
Taxonomy Mappings
Mapped Taxonomy Name
Node ID
Fit
Mapped Node Name
7 Pernicious Kingdoms
Unsafe Reflection
The CERT Oracle Secure Coding Standard for Java (2011)
SEC06-J
Do not use reflection to increase accessibility of classes, methods, or fields
Description
This table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
