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Weakness · ClassCWE-116

CWE-116: Improper Encoding or Escaping of Output

Likelihood of exploit: HighKEV-linkedClass

As of 2026-10-05, CWE-116 (Improper Encoding or Escaping of Output) underlies 5 CVEs tracked by Threadlinqs, 1 of them in the CISA Known Exploited Vulnerabilities catalog, and is cited by 20 tracked threats. MITRE rates its likelihood of exploit as High.

CVEs
5Mapped to CWE-116
CISA KEV
1Exploited in the wild
Critical
0CVSS v3 critical CVEs
Threats
20Tracked campaigns citing it
Likelihood
HighMITRE likelihood of exploit

Last updated:

What is CWE-116?

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.

CWE-116 is a class-level weakness in MITRE’s Common Weakness Enumeration, with a MITRE likelihood of exploit of High. Applicable platforms: Language: Not Language-Specific; Technology: Not Technology-Specific; Technology: AI/ML; Technology: Database Server; Technology: Web Server.

Source: MITRE CWE (CWE-116 definition, reproduced verbatim). Counts and linkage below are Threadlinqs data.

Consequences

  • Integrity — Modify Application Data. The communications between components can be modified in unexpected ways. Unexpected commands can be executed, bypassing other security mechanisms. Incoming data can be misinterpreted.
  • Integrity, Confidentiality, Availability, Access Control — Execute Unauthorized Code or Commands. The communications between components can be modified in unexpected ways. Unexpected commands can be executed, bypassing other security mechanisms. Incoming data can be misinterpreted.
  • Confidentiality — Bypass Protection Mechanism. The communications between components can be modified in unexpected ways. Unexpected commands can be executed, bypassing other security mechanisms. Incoming data can be misinterpreted.

Source: MITRE CWE, common consequences.

How CWE-116 is exploited in the wild

Threadlinqs maps 5 CVEs to CWE-116, published between 2026-06-04 and 2026-09-07. 1 is listed in CISA’s Known Exploited Vulnerabilities catalog, the authoritative record of exploitation in the wild. By CVSS v3 severity the set splits into 3 high, 1 medium. The highest EPSS score in the set is 9.9% (CVE-2026-20245), the modelled probability of exploitation in the next 30 days. 20 tracked threats reference CWE-116 directly or through a CVE it covers; the most recent is “Click2Shell WordPress Exploit Chain Lets Attackers Gain RCE With a Single Malicious Link” (2026-09-19). Affected products concentrate in Cisco (1), ash-project (1), ericcornelissen (1), among 5 vendors in total.

Vulnerabilities (CVEs)

All 5 CVEs mapped to CWE-116, CISA KEV first, then by CVSS score.

Affected vendors

  • Cisco — 1 CVE
  • ash-project — 1 CVE
  • ericcornelissen — 1 CVE
  • fast-uri — 1 CVE
  • pgadmin.org — 1 CVE

Threat activity

20 tracked threats cite CWE-116:

Mitigations

  • Architecture and Design / Libraries or Frameworks: 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 encode outputs in a manner less prone to error. Alternately, use built-in functions, but consider using wrappers in case those functions are discovered to have a vulnerability.
  • Architecture and Design / Parameterization: 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 generated. For example, stored procedures can enforce database query structure and reduce the likelihood of SQL injection.
  • Architecture and Design, Implementation: 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.
  • 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 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.
  • Architecture and Design: Use input validation as a defense-in-depth measure to reduce the likelihood of output encoding errors (see CWE-20).
  • Requirements: Fully specify which encodings are required by components that will be communicating with each other.
  • Implementation: When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.

Source: MITRE CWE, potential mitigations.

Detection methods (MITRE CWE)

  • Automated Static Analysis (effectiveness: Moderate): 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, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Source: MITRE CWE, detection methods. Threadlinqs detection rules for the threats above are Blue tier and higher.