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-757 Base Incompleto
Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')
This vulnerability occurs when a protocol or system allows negotiating a security algorithm (like encryption) but chooses a weaker option than the strongest one both parties support, creating an…
Definición
What is CWE-757?
This vulnerability occurs when a protocol or system allows negotiating a security algorithm (like encryption) but chooses a weaker option than the strongest one both parties support, creating an unnecessary security gap.
This flaw, often called an algorithm downgrade attack, happens because the negotiation process doesn't prioritize the most secure mutual option. Attackers can exploit this by interfering with the handshake to force the use of a broken or outdated algorithm, making subsequent attacks like decryption or spoofing significantly easier.
From a developer's perspective, the danger is that the system operates without alerting users to the reduced protection. For example, if an attacker forces a connection to use basic encryption instead of strong AES-256, they can later decrypt traffic with minimal effort, bypassing the intended security entirely. The core fix is to implement negotiation logic that always selects the strongest mutually-available algorithm and rejects weak fallbacks.
Impacto en el mundo real
Real-world CVEs caused by CWE-757
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Attacker can select an older version of the software to exploit its vulnerabilities.
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Improper prioritization of encryption ciphers during negotiation leads to use of a weaker cipher.
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chain: SSL/TLS implementation disables a verification step (CWE-325) that enables a downgrade attack to a weaker protocol.
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Telnet protocol implementation allows downgrade to weaker authentication and encryption using an Adversary-in-the-Middle AITM attack.
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SSH server implementation allows override of configuration setting to use weaker authentication schemes. This may be a composite with CWE-642.
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 pseudo
MITRE no ha publicado un ejemplo de código para esta CWE. El patrón siguiente es ilustrativo — consulta Recursos para referencias canónicas.
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
// Untrusted input flows directly into the sensitive sink.
return executeUnsafe(input);
} Ejemplo de código seguro
Secure 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-757
- Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
- Implementation Validate input at trust boundaries; use allowlists, not denylists.
- Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
- Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
- Operation Monitor logs for the runtime signals listed in the next section.
Señales de detección
How to detect CWE-757
Plexicus detecta automáticamente CWE-757 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.
Preguntas frecuentes ¿Qué es CWE-757?
¿Qué gravedad tiene CWE-757?
¿Qué lenguajes o plataformas se ven afectados por CWE-757?
¿Cómo puedo prevenir CWE-757?
¿Cómo detecta y corrige Plexicus CWE-757?
¿Dónde puedo aprender más sobre CWE-757?
Frequently asked questions
¿Qué es CWE-757?
This vulnerability occurs when a protocol or system allows negotiating a security algorithm (like encryption) but chooses a weaker option than the strongest one both parties support, creating an unnecessary security gap.
¿Qué gravedad tiene CWE-757?
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-757?
MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.
¿Cómo puedo prevenir CWE-757?
Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.
¿Cómo detecta y corrige Plexicus CWE-757?
El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-757 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-757?
MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/757.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.
Debilidades relacionadas
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