CWE-757 Base Incomplete

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…

Definition

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 Attackers can exploit this by interfering with the handshake to force the use of a broken or outdated algorithm, making subsequent attacks like decryption or spoofing significantly easier.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.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-757

  • CVE-2006-4302

    Attacker can select an older version of the software to exploit its vulnerabilities.

  • CVE-2006-4407

    Improper prioritization of encryption ciphers during negotiation leads to use of a weaker cipher.

  • CVE-2005-2969

    chain: SSL/TLS implementation disables a verification step (CWE-325) that enables a downgrade attack to a weaker protocol.

  • CVE-2001-1444

    Telnet protocol implementation allows downgrade to weaker authentication and encryption using an Adversary-in-the-Middle AITM attack.

  • CVE-2002-1646

    SSH server implementation allows override of configuration setting to use weaker authentication schemes. This may be a composite with CWE-642.

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    Identifiziere einen Codepfad, der nicht vertrauenswürdige Eingaben ohne Validierung verarbeitet.

  2. 2

    Erzeuge eine Payload, die das unsichere Verhalten auslöst — Injection, Traversal, Overflow oder Logik-Missbrauch.

  3. 3

    Liefere die Payload über einen normalen Request aus und beobachte die Reaktion der Anwendung.

  4. 4

    Iteriere, bis die Antwort Daten preisgibt, Angreifer-Code ausführt oder Berechtigungen eskaliert.

Verwundbares Codebeispiel

Vulnerable pseudo

MITRE hat kein Codebeispiel für diese CWE veröffentlicht. Das untenstehende Muster ist illustrativ — kanonische Referenzen findest du unter Ressourcen.

Verwundbar pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
Sicheres Codebeispiel

Secure pseudo

Sicher 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.
Präventions-Checkliste

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.
Erkennungssignale

How to detect CWE-757

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.)

Plexicus Auto-Fix

Plexicus erkennt CWE-757 automatisch und öffnet in unter 60 Sekunden einen Fix-PR.

Codex Remedium scannt jeden Commit, identifiziert genau diese Schwachstelle und liefert einen reviewer-ready Pull Request mit dem Patch. Keine Tickets. Keine Hand-offs.

Demo anfordern Plexicus kostenlos testen
Häufig gestellte Fragen

Frequently asked questions

Was ist 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.

Wie gravierend ist CWE-757?

MITRE hat für diese Schwachstelle keine Exploit-Wahrscheinlichkeit veröffentlicht. Behandle sie als mittlere Auswirkung, bis dein Threat Model anderes belegt.

Welche Sprachen oder Plattformen sind von CWE-757 betroffen?

MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.

Wie kann ich CWE-757 verhindern?

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.

Wie erkennt und behebt Plexicus CWE-757?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-757 bei jedem Commit. Bei einem Treffer öffnet unser Codex-Remedium-Agent einen Fix-PR mit korrigiertem Code, Tests und einer einzeiligen Zusammenfassung für den Reviewer.

Wo erfahre ich mehr über CWE-757?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/757.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-757

CWE-693 Parent

Protection Mechanism Failure

This weakness occurs when software either lacks a necessary security control, implements one that is too weak, or fails to activate an…

CWE-1039 Sibling

Inadequate Detection or Handling of Adversarial Input Perturbations in Automated Recognition Mechanism

This vulnerability occurs when a system uses automated AI or machine learning to classify complex inputs like images, audio, or text, but…

CWE-1248 Sibling

Semiconductor Defects in Hardware Logic with Security-Sensitive Implications

A security-critical hardware component contains physical flaws in its semiconductor material, which can cause it to malfunction and…

CWE-1253 Sibling

Incorrect Selection of Fuse Values

This vulnerability occurs when a hardware security fuse is incorrectly programmed to represent a 'secure' state as logic 0 (unblown). An…

CWE-1269 Sibling

Product Released in Non-Release Configuration

This vulnerability occurs when a product ships to customers while still configured with its pre-production or manufacturing settings,…

CWE-1278 Sibling

Missing Protection Against Hardware Reverse Engineering Using Integrated Circuit (IC) Imaging Techniques

This vulnerability occurs when hardware lacks safeguards against physical inspection, allowing attackers to extract sensitive data by…

CWE-1291 Sibling

Public Key Re-Use for Signing both Debug and Production Code

This vulnerability occurs when the same cryptographic key is used to sign both development/debug software builds and final production…

CWE-1318 Sibling

Missing Support for Security Features in On-chip Fabrics or Buses

This vulnerability occurs when the communication channels (fabrics or buses) within a chip lack built-in or enabled security features,…

CWE-1319 Sibling

Improper Protection against Electromagnetic Fault Injection (EM-FI)

This vulnerability occurs when a hardware device lacks sufficient shielding against electromagnetic interference, allowing attackers to…

Ressourcen

Further reading

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