CAPEC Details
Name HTTP Response Smuggling
Likelyhood of attack Typical severity
Low Medium
Summary An attacker injects content into a server response that is interpreted differently by intermediaries than it is by the target browser. To do this, it takes advantage of inconsistent or incorrect interpretations of the HTTP protocol by various applications. For example, it might use different block terminating characters (CR or LF alone), adding duplicate header fields that browsers interpret as belonging to separate responses, or other techniques. Consequences of this attack can include response-splitting, cross-site scripting, apparent defacement of targeted sites, cache poisoning, or similar actions.
Prerequisites The targeted server must allow the attacker to insert content that will appear in the server's response.
Solutions Design: Employ strict adherence to interpretations of HTTP messages wherever possible. Implementation: Encode header information provided by user input so that user-supplied content is not interpreted by intermediaries.
Related Weaknesses
CWE ID Description
CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
CWE-436 Interpretation Conflict
Related CAPECS
CAPEC ID Description
CAPEC-33 HTTP Request Smuggling results from the discrepancies in parsing HTTP requests between HTTP entities such as web caching proxies or application firewalls. Entities such as web servers, web caching proxies, application firewalls or simple proxies often parse HTTP requests in slightly different ways. Under specific situations where there are two or more such entities in the path of the HTTP request, a specially crafted request is seen by two attacked entities as two different sets of requests. This allows certain requests to be smuggled through to a second entity without the first one realizing it.
CAPEC-220 An adversary takes advantage of weaknesses in the protocol by which a client and server are communicating to perform unexpected actions. Communication protocols are necessary to transfer messages between client and server applications. Moreover, different protocols may be used for different types of interactions. For example, an authentication protocol might be used to establish the identities of the server and client while a separate messaging protocol might be used to exchange data. If there is a weakness in a protocol used by the client and server, an attacker might take advantage of this to perform various types of attacks. For example, if the attacker is able to manipulate an authentication protocol, the attacker may be able spoof other clients or servers. If the attacker is able to manipulate a messaging protocol, the may be able to read sensitive information or modify message contents. This attack is often made easier by the fact that many clients and servers support multiple protocols to perform similar roles. For example, a server might support several different authentication protocols in order to support a wide range of clients, including legacy clients. Some of the older protocols may have vulnerabilities that allow an attacker to manipulate client-server interactions.
Taxonomy: WASC
Entry ID Entry Name
27 HTTP Response Smuggling