CWE-296: Improper Following of a Certificate's Chain of Trust

Definición

What is CWE-296?

This vulnerability occurs when software fails to properly validate the entire certificate chain back to a trusted root authority. This mistake can cause the system to incorrectly trust a certificate and the resource it represents, creating a security gap.

A certificate's trustworthiness isn't inherent; it's derived from a verifiable chain linking it back to a root certificate you already trust. If your code only checks the first link—or skips any intermediate certificates—you haven't actually verified the chain. This is like trusting an ID card because it looks official, without checking if the issuing authority is legitimate and properly authorized the person who issued it. The chain can break in several common ways. These include accepting a self-signed certificate (unless it's the designated root), failing to validate every intermediate certificate's constraints and signatures, or relying on a root certificate that has been compromised. Each skipped check creates an opportunity for an attacker to present a fraudulent certificate that your software will incorrectly accept as valid.

Impacto en el mundo real

Real-world CVEs caused by CWE-296

CVE-2016-2402

Server allows bypass of certificate pinning by sending a chain of trust that includes a trusted CA that is not pinned.
CVE-2008-4989

Verification function trusts certificate chains in which the last certificate is self-signed.
CVE-2012-5821

Chain: Web browser uses a TLS-related function incorrectly, preventing it from verifying that a server's certificate is signed by a trusted certification authority (CA).
CVE-2009-3046

Web browser does not check if any intermediate certificates are revoked.
CVE-2009-0265

chain: DNS server does not correctly check return value from the OpenSSL EVP_VerifyFinal function allows bypass of validation of the certificate chain.
CVE-2009-0124

chain: incorrect check of return value from the OpenSSL EVP_VerifyFinal function allows bypass of validation of the certificate chain.
CVE-2002-0970

File-transfer software does not validate Basic Constraints of an intermediate CA-signed certificate.
CVE-2002-0862

Cryptographic API, as used in web browsers, mail clients, and other software, does not properly validate Basic Constraints.

Cómo lo explotan los atacantes

Ruta del atacante paso a paso

1
Identifica una ruta de código que maneje entrada no confiable sin validación.
2
Crea un payload que ejercite el comportamiento inseguro — inyección, traversal, overflow o abuso de lógica.
3
Envía el payload a través de una solicitud normal y observa la reacción de la aplicación.
4
Itera hasta que la respuesta filtre datos, ejecute código del atacante o escale privilegios.

Ejemplo de código vulnerable

Vulnerable C

This code checks the certificate of a connected peer.

Vulnerable C

if ((cert = SSL_get_peer_certificate(ssl)) && host)
  	foo=SSL_get_verify_result(ssl);
  if ((X509_V_OK==foo) || X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN==foo))
```
// certificate looks good, host can be trusted*

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-296

Architecture and Design Ensure that proper certificate checking is included in the system design.
Implementation Understand, and properly implement all checks necessary to ensure the integrity of certificate trust integrity.
Implementation If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the full chain of trust.

Señales de detección

How to detect CWE-296

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.)

CWE-296

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Preguntas frecuentes

Frequently asked questions

¿Qué es CWE-296?

This vulnerability occurs when software fails to properly validate the entire certificate chain back to a trusted root authority. This mistake can cause the system to incorrectly trust a certificate and the resource it represents, creating a security gap.

¿Qué gravedad tiene CWE-296?

MITRE califica la probabilidad de explotación como Baja — la explotación es poco frecuente, pero la debilidad debe corregirse cuando se descubra.

¿Qué lenguajes o plataformas se ven afectados por CWE-296?

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

¿Cómo puedo prevenir CWE-296?

Ensure that proper certificate checking is included in the system design. Understand, and properly implement all checks necessary to ensure the integrity of certificate trust integrity.

¿Cómo detecta y corrige Plexicus CWE-296?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-296 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-296?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/296.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-296

CWE-295 Padre

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Reservar Pentest

Improper Following of a Certificate's Chain of Trust

What is CWE-296?

Real-world CVEs caused by CWE-296

Ruta del atacante paso a paso

Vulnerable C

Secure pseudo

How to prevent CWE-296

How to detect CWE-296

Don't catalog this weakness. Prove it's reachable.

Frequently asked questions

Weaknesses related to CWE-296

Improper Certificate Validation

Improper Validation of Certificate with Host Mismatch

Improper Validation of Certificate Expiration

Improper Check for Certificate Revocation

Missing Validation of OpenSSL Certificate

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`