CWE-117 Base Borrador Medium likelihood

Improper Output Neutralization for Logs

This vulnerability occurs when an application creates log entries using unvalidated external data, allowing attackers to inject malicious characters or commands that can corrupt log files, trigger…

Definición

What is CWE-117?

This vulnerability occurs when an application creates log entries using unvalidated external data, allowing attackers to inject malicious characters or commands that can corrupt log files, trigger parsing errors, or enable log injection attacks.
Log injection happens when user-supplied data containing special characters like newlines (\n), carriage returns (\r), or log-specific control sequences is written directly into log files without proper sanitization. Attackers can exploit this to forge fake log entries, break log file formatting, or obfuscate their malicious activities by injecting deceptive lines that mislead forensic analysis. To prevent this, developers should treat log entries as structured data rather than free-form text. Always sanitize or encode external inputs before writing them to logs, using appropriate logging frameworks that automatically handle escaping. Consider using parameterized logging functions that separate data from the log message template, which neutralizes dangerous characters while maintaining log integrity and readability.
Vulnerability Diagram CWE-117
Log Injection Username bob\nADMIN: login OK app.log 12:00 INFO login user=bob ADMIN: login OK ← forged 12:01 INFO list page SOC analyst misled by fake events Newlines in input forge log entries and hide attacker traces.
Impacto en el mundo real

Real-world CVEs caused by CWE-117

  • CVE-2006-4624

    Chain: inject fake log entries with fake timestamps using CRLF injection

Cómo lo explotan los atacantes

Ruta del atacante paso a paso

  1. 1

    The following web application code attempts to read an integer value from a request object. If the parseInt call fails, then the input is logged with an error message indicating what happened.

  2. 2

    If a user submits the string "twenty-one" for val, the following entry is logged:

  3. 3

    - INFO: Failed to parse val=twenty-one

  4. 4

    However, if an attacker submits the string "twenty-one%0a%0aINFO:+User+logged+out%3dbadguy", the following entry is logged:

  5. 5

    - INFO: Failed to parse val=twenty-one - INFO: User logged out=badguy

Ejemplo de código vulnerable

Vulnerable Java

The following web application code attempts to read an integer value from a request object. If the parseInt call fails, then the input is logged with an error message indicating what happened.

Vulnerable Java 
String val = request.getParameter("val");
  try {
  		int value = Integer.parseInt(val);
  }
  catch (NumberFormatException) {
  	log.info("Failed to parse val = " + val);
  }
  ...
Ejemplo de código seguro

Secure pseudo

Seguro pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Lista de prevención

How to prevent CWE-117

  • Implementation Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
  • Implementation Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component.
  • Implementation Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Señales de detección

How to detect CWE-117

Automated Static Analysis High

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.)

Auto-corrección de Plexicus

Plexicus detecta automáticamente CWE-117 y abre un PR de corrección en menos de 60 segundos.

Codex Remedium escanea cada commit, identifica esta debilidad concreta y entrega un pull request listo para revisión con el parche. Sin tickets. Sin traspasos.

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Preguntas frecuentes

Frequently asked questions

¿Qué es CWE-117?

This vulnerability occurs when an application creates log entries using unvalidated external data, allowing attackers to inject malicious characters or commands that can corrupt log files, trigger parsing errors, or enable log injection attacks.

¿Qué gravedad tiene CWE-117?

MITRE califica la probabilidad de explotación como Media — la explotación es realista pero suele requerir condiciones específicas.

¿Qué lenguajes o plataformas se ven afectados por CWE-117?

MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.

¿Cómo puedo prevenir CWE-117?

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and…

¿Cómo detecta y corrige Plexicus CWE-117?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-117 en cada commit. Cuando hay coincidencia, nuestro agente Codex Remedium abre un PR de corrección con el código corregido, las pruebas y un resumen de una línea para el revisor.

¿Dónde puedo aprender más sobre CWE-117?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/117.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-117

CWE-116 Padre

Improper Encoding or Escaping of Output

This vulnerability occurs when an application builds a structured message—like a query, command, or request—for another component but…

CWE-644 Hermano

Improper Neutralization of HTTP Headers for Scripting Syntax

This vulnerability occurs when an application fails to properly sanitize or escape user-controlled data placed within HTTP response…

CWE-838 Hermano

Inappropriate Encoding for Output Context

This vulnerability occurs when a system uses one type of encoding for its output, but the component receiving that data expects a…

Recursos

Further reading

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