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Weakness · High

CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

What it is

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.

4 exploited in the wildMITRE CWE 4.19.1

Severity (our rating)
High
Likelihood of exploit
Not rated by MITRE
Introduced during
Implementation
Exploited in the wild
4 known exploited CVEs

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 This weakness is usually the result of the usage of outdated or incompatible HTTP protocol versions in the HTTP agents.

What an attacker can do

  • Unexpected State (Integrity, Non-Repudiation, Access Control)
  • Hide Activities (Integrity, Non-Repudiation, Access Control)
  • Bypass Protection Mechanism (Integrity, Non-Repudiation, Access Control)

How to prevent it

Implementation

  • Use a web server that employs a strict HTTP parsing procedure, such as Apache.
  • Use only SSL communication.
  • Terminate the client session after each request.

System Configuration

  • Turn all pages to non-cacheable.

While the code is being fixed, a WAF in blocking mode stops HTTP request smuggling patterns at the edge.

How to find it

  • Automated Static Analysis. 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-444 on MITRE's CWE site

Exploited in the wild: 4 CVEs

Vulnerabilities caused by CWE-444 that attackers have used, from CISA's Known Exploited Vulnerabilities catalog, newest first.

All known exploited vulnerabilities

The Dome

Block it at the edge while you fix it

The Dome's WAF runs the OWASP Core Rule Set in blocking mode and stops HTTP request smuggling patterns before they reach your application.

See the Dome

T Academy

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Source: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.