CWE-441: Unintended Proxy or Intermediary ('Confused Deputy')
Weakness ID: 441
Vulnerability Mapping:ALLOWEDThis CWE ID could be used to map to real-world vulnerabilities in limited situations requiring careful review
(with careful review of mapping notes)
Abstraction:
ClassClass - 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.
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Description
The product receives a request, message, or directive from an upstream component, but the product does not sufficiently preserve the original source of the request before forwarding the request to an external actor that is outside of the product's control sphere. This causes the product to appear to be the source of the request, leading it to act as a proxy or other intermediary between the upstream component and the external actor.
Extended Description
If an attacker cannot directly contact a target, but the product has access to the target, then the attacker can send a request to the product and have it be forwarded to the target. The request would appear to be coming from the product's system, not the attacker's system. As a result, the attacker can bypass access controls (such as firewalls) or hide the source of malicious requests, since the requests would not be coming directly from the attacker.
Since proxy functionality and message-forwarding often serve a legitimate purpose, this issue only becomes a vulnerability when:
The product runs with different privileges or on a different system, or otherwise has different levels of access than the upstream component;
The attacker is prevented from making the request directly to the target; and
The attacker can create a request that the proxy does not explicitly intend to be forwarded on the behalf of the requester. Such a request might point to an unexpected hostname, port number, hardware IP, or service. Or, the request might be sent to an allowed service, but the request could contain disallowed directives, commands, or resources.
Alternate Terms
Confused Deputy:
This weakness is sometimes referred to as the "Confused deputy" problem, in which an attacker misused the authority of one victim (the "confused deputy") when targeting another victim.
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
Non-Repudiation Access Control
Technical Impact: Gain Privileges or Assume Identity; Hide Activities; Execute Unauthorized Code or Commands
Potential Mitigations
Phase: Architecture and Design
Enforce the use of strong mutual authentication mechanism between the two parties.
Phase: Architecture and Design
Whenever a product is an intermediary or proxy for
transactions between two other components, the proxy core
should not drop the identity of the initiator of the
transaction. The immutability of the identity of the
initiator must be maintained and should be forwarded all the
way to the target.
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.
Base - 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.
Base - 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.
Base - 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.
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 "Architectural Concepts" (CWE-1008)
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 "Hardware Design" (CWE-1194)
Nature
Type
ID
Name
MemberOf
Category - a CWE entry that contains a set of other entries that share a common characteristic.
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
REALIZATION: This weakness is caused during implementation of an architectural security tactic.
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
Class: Not Language-Specific
(Undetermined Prevalence)
Operating Systems
Class: Not OS-Specific
(Undetermined Prevalence)
Architectures
Class: Not Architecture-Specific
(Undetermined Prevalence)
Technologies
Class: Not Technology-Specific
(Undetermined Prevalence)
Demonstrative Examples
Example 1
A SoC contains a microcontroller (running ring-3
(least trusted ring) code), a Memory Mapped Input Output
(MMIO) mapped IP core (containing design-house secrets),
and a Direct Memory Access (DMA) controller, among several
other compute elements and peripherals. The SoC implements
access control to protect the registers in the IP core
(which registers store the design-house secrets) from
malicious, ring-3 (least trusted ring) code executing on
the microcontroller. The DMA controller, however, is not
blocked off from accessing the IP core for functional
reasons.
(bad code)
Example Language: Other
The code in ring-3 (least trusted ring) of the
microcontroller attempts to directly read the protected
registers in IP core through MMIO transactions. However,
this attempt is blocked due to the implemented access
control. Now, the microcontroller configures the DMA core
to transfer data from the protected registers to a memory
region that it has access to. The DMA core, which is
acting as an intermediary in this transaction, does not
preserve the identity of the microcontroller and, instead,
initiates a new transaction with its own identity. Since
the DMA core has access, the transaction (and hence, the
attack) is successful.
The weakness here is that the intermediary or the
proxy agent did not ensure the immutability of the
identity of the microcontroller initiating the
transaction.
(good code)
Example Language: Other
The DMA
core forwards this transaction with the identity of the
code executing on the microcontroller, which is the
original initiator of the end-to-end transaction. Now the
transaction is blocked, as a result of forwarding the
identity of the true initiator which lacks the permission
to access the confidential MMIO mapped IP core.
FTP bounce attack. The design of the protocol allows an attacker to modify the PORT command to cause the FTP server to connect to other machines besides the attacker's.
URL-downloading library automatically follows redirects to file:// and scp:// URLs
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.
(this CWE ID could be used to map to real-world vulnerabilities in limited situations requiring careful review)
Reason:
Abstraction
Rationale:
This CWE entry is a Class and might have Base-level children that would be more appropriate
Comments:
Examine children of this entry to see if there is a better fit
Notes
Relationship
This weakness has a chaining relationship with CWE-668 (Exposure of Resource to Wrong Sphere) because the proxy effectively provides the attacker with access to the target's resources that the attacker cannot directly obtain.
Theoretical
It could be argued that the "confused deputy" is a fundamental aspect of most vulnerabilities that require an active attacker. Even for common implementation issues such as buffer overflows, SQL injection, OS command injection, and path traversal, the vulnerable program already has the authorization to run code or access files. The vulnerability arises when the attacker causes the program to run unexpected code or access unexpected files.
Maintenance
This could possibly be considered as an emergent resource.
Per Intel Corporation suggestion, added language to be inclusive to hardware: updated Demonstrative_Examples, Description, Extended_Description, Applicable_Platforms, Potential_Mitigation, Common_Consequences, References
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.
