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.)
CWE-441 Class Draft
Unintended Proxy or Intermediary ('Confused Deputy')
A confused deputy vulnerability occurs when a system receives a request from a client and forwards it to an external destination without properly identifying the original source. This makes the…
Definition
What is CWE-441?
A confused deputy vulnerability occurs when a system receives a request from a client and forwards it to an external destination without properly identifying the original source. This makes the system appear to be the originator of the request, effectively turning it into an unintended proxy for the client.
Attackers exploit this flaw when they cannot reach a target system directly. By sending a malicious request to your vulnerable application, they can have it relayed to the protected target. Since the request now originates from your system's IP address and context, it can bypass network firewalls, IP-based allowlists, and hide the attacker's true location, enabling unauthorized access or actions.
This becomes a critical security issue only under specific conditions: your application must have higher privileges or different network access than the initial requester; the attacker must be blocked from contacting the target directly; and the attacker must be able to craft a request that your application forwards unintentionally. This often involves specifying an unexpected host, port, internal IP, or a restricted command within an otherwise permitted service request.
Real-world impact
Real-world CVEs caused by CWE-441
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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.
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RPC portmapper could redirect service requests from an attacker to another entity, which thinks the requests came from the portmapper.
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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.
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Web server allows attackers to request a URL from another server, including other ports, which allows proxied scanning.
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CGI script accepts and retrieves incoming URLs.
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Bounce attack allows access to TFTP from trusted side.
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Web-based mail program allows internal network scanning using a modified POP3 port number.
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URL-downloading library automatically follows redirects to file:// and scp:// URLs
How attackers exploit it
Step-by-step attacker path
- 1
Identify a code path that handles untrusted input without validation.
- 2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
- 3
Deliver the payload through a normal request and observe the application's reaction.
- 4
Iterate until the response leaks data, executes attacker code, or escalates privileges.
Vulnerable code example
Vulnerable Other
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. Secure code example
Secure Other
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. What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-441
- 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.
Detection signals
How to detect CWE-441
Plexicus auto-detects CWE-441 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-441?
How serious is CWE-441?
What languages or platforms are affected by CWE-441?
How can I prevent CWE-441?
How does Plexicus detect and fix CWE-441?
Where can I learn more about CWE-441?
Frequently asked questions
What is CWE-441?
A confused deputy vulnerability occurs when a system receives a request from a client and forwards it to an external destination without properly identifying the original source. This makes the system appear to be the originator of the request, effectively turning it into an unintended proxy for the client.
How serious is CWE-441?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-441?
MITRE lists the following affected platforms: Not OS-Specific, Not Architecture-Specific, Not Technology-Specific.
How can I prevent CWE-441?
Enforce the use of strong mutual authentication mechanism between the two parties. 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.
How does Plexicus detect and fix CWE-441?
Plexicus's SAST engine matches the data-flow signature for CWE-441 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-441?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/441.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-441
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CWE-15 Sibling
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CWE-384 Sibling
Session Fixation
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CWE-470 Sibling
Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')
This vulnerability occurs when an application uses unvalidated external input, like a URL parameter or form field, to dynamically decide…
CWE-601 Sibling
URL Redirection to Untrusted Site ('Open Redirect')
An open redirect vulnerability occurs when a web application uses unvalidated user input to determine the destination of a redirect,…
CWE-611 Sibling
Improper Restriction of XML External Entity Reference
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CWE-73 Sibling
External Control of File Name or Path
This vulnerability occurs when an application uses unvalidated user input to construct file or directory paths for filesystem operations.
CWE-918 Sibling
Server-Side Request Forgery (SSRF)
Server-Side Request Forgery (SSRF) occurs when a web application fetches a remote resource based on user-controlled input, but fails to…
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