Unintended Proxy or Intermediary ('Confused Deputy')

Opis

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.

Inne nazwy

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.

Skutki

• Non-Repudiation, Access Control

  Gain Privileges or Assume Identity; Hide Activities; Execute Unauthorized Code or Commands

Zapobieganie

• 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.

Przykłady podatności

• 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.
• CVE-2001-1484 Bounce attack allows access to TFTP from trusted side.
• CVE-2010-1637 Web-based mail program allows internal network scanning using a modified POP3 port number.
• CVE-2009-0037 URL-downloading library automatically follows redirects to file:// and scp:// URLs

Słabość nadrzędna

• CWE-610 Externally Controlled Reference to a Resource in Another Sphere

Może prowadzić do

• CWE-668 Exposure of Resource to Wrong Sphere

Słabości podrzędne

• CWE-918 Server-Side Request Forgery (SSRF)
• CWE-1021 Improper Restriction of Rendered UI Layers or Frames

Kiedy powstaje

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

Dotyczy

Not Language-Specific, Not OS-Specific, Not Architecture-Specific, Not Technology-Specific

Uwagi

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.

Źródła

1. The Confused Deputy (or why capabilities might have been invented) — Norm Hardy, 1988
2. Validation Vulnerabilities — moparisthebest, 2015