CWE-116: Improper Encoding or Escaping of Output

Description:
The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

Extended Description:
Improper encoding or escaping can allow attackers to change the commands that are sent to another component, inserting malicious commands instead. 
             Most products follow a certain protocol that uses structured messages for communication between components, such as queries or commands. These structured messages can contain raw data interspersed with metadata or control information. For example, "GET /index.html HTTP/1.1" is a structured message containing a command ("GET") with a single argument ("/index.html") and metadata about which protocol version is being used ("HTTP/1.1"). 
             If an application uses attacker-supplied inputs to construct a structured message without properly encoding or escaping, then the attacker could insert special characters that will cause the data to be interpreted as control information or metadata. Consequently, the component that receives the output will perform the wrong operations, or otherwise interpret the data incorrectly.

Affected languages: Not Language-Specific
Affected technologies: Not Technology-Specific, AI/ML, Database Server, Web Server
Parent weaknesses: CWE-707

Consequences:
  - Integrity: Modify Application Data
  - Integrity: Execute Unauthorized Code or Commands
  - Confidentiality: Bypass Protection Mechanism

Detection methods:
  - Automated Static Analysis: This weakness can often be detected using automated static analysis tools. Many modern tools use data flow analysis or constraint-based techniques to minimize the number of false positives.
  - Automated Dynamic Analysis: This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, a

Mitigations:
  - [Architecture and Design] Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. 
                   For example, consider using the ESAPI Encoding control [REF-45] or a similar tool, library, or framework. These will help the programmer en
  - [Architecture and Design] If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is
  - [Architecture and Design] Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messa
  - [Architecture and Design] In some cases, input validation may be an important strategy when output encoding is not a complete solution. For example, you may be providing the same output that will be processed by multiple consumers that use different encodings or representations. In other cases, you may be required to allow u

Demonstrative examples:
This code displays an email address that was submitted as part of a form.
The value read from the form parameter is reflected back to the client browser without having been encoded prior to output, allowing various XSS attacks (CWE-79).
<% String email = request.getParameter("email"); %> ... Email Address: <%= email %>

Consider a chat application in which a front-end web application communicates with a back-end server. The back-end is legacy code that does not perform authentication or authorization, so the front-end must implement it. The chat protocol supports two commands, SAY and BAN, although only administrators can use the BAN command. Each argument must be separated by a single space. The raw inputs are URL-encoded. The messaging protocol allows multiple commands to be specified on the same line if they are separated by a "|" character.
First let's look at the back end command processor code
$inputString = readLineFromFileHandle($serverFH); 
                      
                      # generate an array of strings separated by the "|" character. 
                      @commands = split(/\|/, $in

Real-world examples:
  - CVE-2021-41232: Chain: authentication routine in Go-based agile development product does not escape user name (CWE-116), allowing LDAP injection (CWE-90)
  - CVE-2008-4636: OS command injection in backup software using shell metacharacters in a filename; correct behavior would require that this filename could not be changed.
  - CVE-2008-0769: Web application does not set the charset when sending a page to a browser, allowing for XSS exploitation when a browser chooses an unexpected encoding.
  - CVE-2008-0005: Program does not set the charset when sending a page to a browser, allowing for XSS exploitation when a browser chooses an unexpected encoding.
  - CVE-2008-5573: SQL injection via password parameter; a strong password might contain "&"