CWE-93 Base Borrador

Improper Neutralization of CRLF Sequences ('CRLF Injection')

This vulnerability occurs when an application uses carriage return and line feed characters (CRLF) to structure data, like separating lines or records, but fails to properly sanitize these sequences…

Definición

What is CWE-93?

This vulnerability occurs when an application uses carriage return and line feed characters (CRLF) to structure data, like separating lines or records, but fails to properly sanitize these sequences from user-supplied input before processing.
CRLF injection, often called 'HTTP Response Splitting' in web contexts, happens because attackers can inject the characters \r\n (CRLF) into input fields. When this unsanitized input is later used to construct structured outputs like HTTP headers, log files, or email headers, the injected characters can create new lines or entries. This allows attackers to manipulate the application's behavior, forge log entries, or inject malicious content that other users might see. To prevent this, developers must rigorously validate and sanitize all user-controlled data that influences output formatting. This involves encoding or stripping CRLF sequences (\r, \n, and their encoded equivalents like %0d%0a) before the data is used in any context where these characters have special meaning, such as HTTP responses, generated files, or system commands.
Vulnerability Diagram CWE-93
CRLF Injection / HTTP Response Splitting Input contains value\r\nSet-Cookie: a=b HTTP Response Set-Header: value ↳ \r\n ← splits headers Set-Cookie: a=b \r\n\r\n <injected body> Browser sees 2 responses / fake page CR/LF chars forge new headers or split response bodies.
Impacto en el mundo real

Real-world CVEs caused by CWE-93

  • CVE-2002-1771

    CRLF injection enables spam proxy (add mail headers) using email address or name.

  • CVE-2002-1783

    CRLF injection in API function arguments modify headers for outgoing requests.

  • CVE-2004-1513

    Spoofed entries in web server log file via carriage returns

  • CVE-2006-4624

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

  • CVE-2005-1951

    Chain: Application accepts CRLF in an object ID, allowing HTTP response splitting.

  • CVE-2004-1687

    Chain: HTTP response splitting via CRLF in parameter related to URL.

Cómo lo explotan los atacantes

Ruta del atacante paso a paso

  1. 1

    The following code segment reads the name of the author of a weblog entry, author, from an HTTP request and sets it in a cookie header of an HTTP response.

  2. 2

    Assuming a string consisting of standard alpha-numeric characters, such as "Jane Smith", is submitted in the request the HTTP response including this cookie might take the following form:

  3. 3

    However, because the value of the cookie is composed of unvalidated user input, the response will only maintain this form if the value submitted for AUTHOR_PARAM does not contain any CR and LF characters. If an attacker submits a malicious string, such as

  4. 4

    then the HTTP response would be split into two responses of the following form:

  5. 5

    The second response is completely controlled by the attacker and can be constructed with any header and body content desired. The ability to construct arbitrary HTTP responses permits a variety of resulting attacks, including:

Ejemplo de código vulnerable

Vulnerable Java

The following code segment reads the name of the author of a weblog entry, author, from an HTTP request and sets it in a cookie header of an HTTP response.

Vulnerable Java 
String author = request.getParameter(AUTHOR_PARAM);
  ...
  Cookie cookie = new Cookie("author", author);
  cookie.setMaxAge(cookieExpiration);
  response.addCookie(cookie);
Payload del atacante

However, because the value of the cookie is composed of unvalidated user input, the response will only maintain this form if the value submitted for AUTHOR_PARAM does not contain any CR and LF characters. If an attacker submits a malicious string, such as

Payload del atacante 
Wiley Hacker\r\nHTTP/1.1 200 OK\r\n
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-93

  • Implementation Avoid using CRLF as a special sequence.
  • Implementation Appropriately filter or quote CRLF sequences in user-controlled input.
Señales de detección

How to detect CWE-93

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-93 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-93?

This vulnerability occurs when an application uses carriage return and line feed characters (CRLF) to structure data, like separating lines or records, but fails to properly sanitize these sequences from user-supplied input before processing.

¿Qué gravedad tiene CWE-93?

MITRE no ha publicado una calificación de probabilidad de explotación para esta debilidad. Trátala como de impacto medio hasta que tu modelo de amenazas demuestre lo contrario.

¿Qué lenguajes o plataformas se ven afectados por CWE-93?

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

¿Cómo puedo prevenir CWE-93?

Avoid using CRLF as a special sequence. Appropriately filter or quote CRLF sequences in user-controlled input.

¿Cómo detecta y corrige Plexicus CWE-93?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-93 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-93?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/93.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-93

CWE-74 Padre

Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

This vulnerability occurs when an application uses untrusted external input to build a command, query, or data structure for another…

CWE-1236 Hermano

Improper Neutralization of Formula Elements in a CSV File

This vulnerability occurs when an application writes user-supplied data into a CSV file without properly sanitizing special characters.…

CWE-75 Hermano

Failure to Sanitize Special Elements into a Different Plane (Special Element Injection)

This vulnerability occurs when an application fails to properly filter or encode user-supplied data containing special characters or…

CWE-77 Hermano

Improper Neutralization of Special Elements used in a Command ('Command Injection')

This vulnerability occurs when an application builds a system command using untrusted user input without properly sanitizing it. An…

CWE-78 Hermano

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

OS Command Injection occurs when an application builds a system command using untrusted, external input without properly sanitizing it.…

CWE-79 Hermano

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

This vulnerability occurs when a web application fails to properly sanitize or encode user-supplied input before displaying it on a…

CWE-88 Hermano

Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')

This vulnerability occurs when an application builds a command string for execution by another component, but fails to properly separate…

CWE-89 Hermano

Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection')

SQL Injection occurs when an application builds a database query using untrusted user input without properly sanitizing it. This allows an…

CWE-91 Hermano

XML Injection (aka Blind XPath Injection)

XML Injection occurs when an application fails to properly validate or escape user-controlled input before including it in XML documents…

Recursos

Further reading

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