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Weakness (CWE)

CWE-444: Inconsistent Interpretation of HTTP Requests

Base Incomplete

The product acts as an intermediary HTTP agent
(such as a proxy or firewall) in the data flow between two
entities such as a client and server, but it does not
interpret malformed HTTP requests or responses in ways that
are consistent with how the messages will be processed by
those entities that are at the ultimate destination.

More detail

HTTP requests or responses ("messages") can be
malformed or unexpected in ways that cause web servers or
clients to interpret the messages in different ways than
intermediary HTTP agents such as load balancers, reverse
proxies, web caching proxies, application firewalls,
etc. For example, an adversary may be able to add duplicate
or different header fields that a client or server might
interpret as one set of messages, whereas the intermediary
might interpret the same sequence of bytes as a different
set of messages. For example, discrepancies can arise in
how to handle duplicate headers like two Transfer-encoding
(TE) or two Content-length (CL), or the malicious HTTP
message will have different headers for TE and
CL.

The inconsistent parsing and interpretation of messages
can allow the adversary to "smuggle" a message to the
client/server without the intermediary being aware of it.

This weakness is usually the result of the usage
of outdated or incompatible HTTP protocol versions in the
HTTP agents.

How to prevent it (4 mitigations)

  1. Implementation

    Use a web server that employs a strict HTTP parsing procedure, such as Apache [REF-433].

  2. Implementation

    Use only SSL communication.

  3. Implementation

    Terminate the client session after each request.

  4. System Configuration

    Turn all pages to non-cacheable.

Source: MITRE CWE-444

All Critical High Medium Low Exploited only Public exploit

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