CWE WEAKNESSES  /  CWE-441

CWE-441

Unintended Proxy or Intermediary ('Confused Deputy')

What it is

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

Impact

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 must be maintained and should be forwarded all the way to the target.

Real-world CVE 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 att
• 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

Related weaknesses

Source: MITRE CWE. View on cwe.mitre.org →