CWE-441: Unintended Proxy or Intermediary ('Confused Deputy')

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 beha

Affected languages: Not Language-Specific
Affected technologies: Not Technology-Specific
Parent weaknesses: CWE-610

Consequences:
  - Non-Repudiation: Gain Privileges or Assume Identity

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 havin

Mitigations:
  - [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

Demonstrative examples:
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 weakness here is t

Real-world examples:
  - 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.
  - CVE-1999-0168: RPC portmapper could redirect service requests from an attacker to another entity, which thinks the requests came from the portmapper.
  - 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.
  - CVE-2002-1484: Web server allows attackers to request a URL from another server, including other ports, which allows proxied scanning.
  - CVE-2004-2061: CGI script accepts and retrieves incoming URLs.