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.

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.

Primary

Resultant

Confused Deputy
This weakness is sometimes referred to as the "Confused deputy" problem, in which an attacker misuses the authority of one victim (the "confused deputy") to use that victim's legitimate (restricted) capabilities to target another victim.

Architecture and Design
REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Non-Repudiation
Access Control
Gain Privileges or Assume Identity
Hide Activities
Execute Unauthorized Code or Commands

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

Architecture and Design
Enforce the use of strong mutual authentication mechanism between the two parties.

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.

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.

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.

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.

CVE-1999-0017
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.
https://www.cve.org/CVERecord?id=CVE-1999-0017

CVE-1999-0168
RPC portmapper could redirect service requests from an attacker to another entity, which thinks the requests came from the portmapper.
https://www.cve.org/CVERecord?id=CVE-1999-0168

CVE-2005-0315
FTP server does not ensure that the IP address in a PORT command is the same as the FTP user's session, allowing port scanning by proxy.
https://www.cve.org/CVERecord?id=CVE-2005-0315

CVE-2002-1484
Web server allows attackers to request a URL from another server, including other ports, which allows proxied scanning.
https://www.cve.org/CVERecord?id=CVE-2002-1484

CVE-2004-2061
CGI script accepts and retrieves incoming URLs.
https://www.cve.org/CVERecord?id=CVE-2004-2061

CVE-2001-1484
Bounce attack allows access to TFTP from trusted side.
https://www.cve.org/CVERecord?id=CVE-2001-1484

CVE-2010-1637
Web-based mail program allows internal network scanning using a modified POP3 port number.
https://www.cve.org/CVERecord?id=CVE-2010-1637

CVE-2009-0037
URL-downloading library automatically follows redirects to file:// and scp:// URLs
https://www.cve.org/CVERecord?id=CVE-2009-0037

Unintended proxy/intermediary

Proxied Trusted Channel

32
Routing Detour

Allowed-with-Review
This CWE entry is a Class and might have Base-level children that would be more appropriate
Examine children of this entry to see if there is a better fit

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.
This could possibly be considered as an emergent resource.
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.

PLOVER
2006-07-19
Draft 3
2006-07-19

Eric Dalci
Cigital
2008-07-01
updated Potential_Mitigations, Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Relationships, Observed_Example, Other_Notes, Taxonomy_Mappings

CWE Content Team
MITRE
2008-11-24
updated Maintenance_Notes, Relationships, Taxonomy_Mappings, Time_of_Introduction

CWE Content Team
MITRE
2010-02-16
updated Taxonomy_Mappings

CWE Content Team
MITRE
2010-04-05
updated Related_Attack_Patterns

CWE Content Team
MITRE
2010-06-21
updated Other_Notes

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2011-06-27
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated Related_Attack_Patterns, Relationships

CWE Content Team
MITRE
2012-10-30
updated Potential_Mitigations

CWE Content Team
MITRE
2013-02-21
updated Alternate_Terms, Applicable_Platforms, Description, Maintenance_Notes, Name, Observed_Examples, References, Relationship_Notes, Relationships, Theoretical_Notes, Type

CWE Content Team
MITRE
2014-07-30
updated Relationships

CWE Content Team
MITRE
2015-12-07
updated Relationships

CWE Content Team
MITRE
2017-01-19
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Modes_of_Introduction, Relationships

CWE Content Team
MITRE
2019-06-20
updated Relationships

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2020-08-14
Per Intel Corporation suggestion, added language to be inclusive to hardware: updated Demonstrative_Examples, Description, Extended_Description, Applicable_Platforms, Potential_Mitigation, Common_Consequences, References

CWE Content Team
MITRE
2020-08-20
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Description, Potential_Mitigations, References, Relationships

CWE Content Team
MITRE
2021-10-28
updated Relationships

CWE Content Team
MITRE
2022-10-13
updated Related_Attack_Patterns

CWE Content Team
MITRE
2023-04-27
updated Detection_Factors, Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Alternate_Terms, Relationships, Weakness_Ordinalities

Arun Kanuparthi, Hareesh Khattri, Parbati K. Manna
Intel Corporation
2020-08-14
Provided demonstrative example

Unintended Proxy/Intermediary