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 Incomplet
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…
Définition
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 Attackers can exploit this by interfering with the handshake to force the use of a broken or outdated algorithm, making subsequent attacks like decryption or spoofing significantly easier.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.
Impact réel
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.
Comment les attaquants l'exploitent
Parcours de l'attaquant étape par étape
- 1
Identifier un chemin de code qui traite des entrées non fiables sans validation.
- 2
Élaborer une charge utile qui exploite le comportement non sécurisé — injection, traversal, débordement ou abus de logique.
- 3
Délivrer la charge utile via une requête normale et observer la réaction de l'application.
- 4
Itérer jusqu'à ce que la réponse divulgue des données, exécute le code de l'attaquant ou élève les privilèges.
Exemple de code vulnérable
Vulnerable pseudo
MITRE n'a pas publié d'exemple de code pour ce CWE. Le motif ci-dessous est illustratif — voir Ressources pour les références canoniques.
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
// Untrusted input flows directly into the sensitive sink.
return executeUnsafe(input);
} Exemple de code sécurisé
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.
Liste de contrôle de prévention
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.
Signaux de détection
How to detect CWE-757
Plexicus détecte automatiquement CWE-757 et ouvre une PR de correction en moins de 60 secondes.
Codex Remedium analyse chaque commit, identifie cette faiblesse précise et livre une pull request prête à être relue avec le correctif. Pas de tickets. Pas de transferts.
Questions fréquentes Qu'est-ce que CWE-757 ?
Quelle est la gravité de CWE-757 ?
Quels langages ou plateformes sont affectés par CWE-757 ?
Comment puis-je prévenir CWE-757 ?
Comment Plexicus détecte et corrige CWE-757 ?
Où puis-je en savoir plus sur CWE-757 ?
Frequently asked questions
Qu'est-ce que 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.
Quelle est la gravité de CWE-757 ?
MITRE n'a pas publié de note de probabilité d'exploitation pour cette faiblesse. Traitez-la comme un impact moyen jusqu'à ce que votre modèle de menace prouve le contraire.
Quels langages ou plateformes sont affectés par CWE-757 ?
MITRE n'a pas spécifié les plateformes affectées pour ce CWE — il peut s'appliquer à la plupart des stacks applicatives.
Comment puis-je prévenir 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.
Comment Plexicus détecte et corrige CWE-757 ?
Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-757 à chaque commit. Lorsqu'une correspondance est trouvée, notre agent Codex Remedium ouvre une PR de correction avec le code corrigé, les tests et un résumé d'une ligne pour le relecteur.
Où puis-je en savoir plus sur CWE-757 ?
MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/757.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.
Faiblesses associées
Weaknesses related to CWE-757
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