What is CWE-116: Improper Encoding or Escaping of Output?+
CWE-116: Improper Encoding or Escaping of Output is a Common Weakness Enumeration (CWE) entry maintained by MITRE. 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. 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.
What are the security consequences of Improper Encoding or Escaping of Output?+
If exploited, CWE-116 (Improper Encoding or Escaping of Output) it can compromise Integrity, Confidentiality, Availability and Access Control, leading to outcomes such as Modify Application Data, Execute Unauthorized Code or Commands and Bypass Protection Mechanism.
How do you prevent or mitigate Improper Encoding or Escaping of Output?+
Recommended mitigations for CWE-116 include: 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 messages. Study all expected communication protocols and data representations to determine the required encoding strategies. 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 user-supplied input to contain control information, such as limited HTML tags that support formatting in a wiki or bulletin board. When this type of requirement must be met, use an extremely strict allowlist to limit which control sequences can be used. Verify that the resulting syntactic structure is what you expect. Use your normal encoding methods for the remainder of the input. Use input validation as a defense-in-depth measure to reduce the likelihood of output encoding errors (see CWE-20).
Which programming languages are affected by Improper Encoding or Escaping of Output?+
CWE-116 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.
What are real-world examples of Improper Encoding or Escaping of Output?+
MITRE documents real CVEs mapped to CWE-116, including CVE-2021-41232, CVE-2008-4636, CVE-2008-0769, CVE-2008-0005 and CVE-2008-5573. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.
What is the difference between a CWE and a CVE?+
A CWE (Common Weakness Enumeration) like CWE-116 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.