CWE-420 Base Draft

Unprotected Alternate Channel

This vulnerability occurs when an application secures its main communication path but leaves a backup or alternative channel with weaker or no protection.

Definition

What is CWE-420?

This vulnerability occurs when an application secures its main communication path but leaves a backup or alternative channel with weaker or no protection.
Think of an application that uses strong encryption for its primary web login but sends password reset codes via unencrypted SMS. An attacker can ignore the fortified main door and easily intercept data through this neglected side channel. This creates a false sense of security, as the overall system is only as strong as its weakest point. Developers often focus all their security efforts on the obvious primary path, forgetting that attackers actively seek out these alternate, less-guarded routes. To prevent this, you must perform a thorough threat model that maps all data flows, not just the primary ones. Apply consistent security controls—like encryption, authentication, and integrity checks—across every channel that handles sensitive data or critical commands. Regularly test both primary and alternate paths during security assessments to ensure your defenses are uniform and comprehensive.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-420

  • CVE-2020-8004

    When the internal flash is protected by blocking access on the Data Bus (DBUS), it can still be indirectly accessed through the Instruction Bus (IBUS).

  • CVE-2002-0567

    DB server assumes that local clients have performed authentication, allowing attacker to directly connect to a process to load libraries and execute commands; a socket interface also exists (another alternate channel), so attack can be remote.

  • CVE-2002-1578

    Product does not restrict access to underlying database, so attacker can bypass restrictions by directly querying the database.

  • CVE-2003-1035

    User can avoid lockouts by using an API instead of the GUI to conduct brute force password guessing.

  • CVE-2002-1863

    FTP service can not be disabled even when other access controls would require it.

  • CVE-2002-0066

    Windows named pipe created without authentication/access control, allowing configuration modification.

  • CVE-2004-1461

    Router management interface spawns a separate TCP connection after authentication, allowing hijacking by attacker coming from the same IP address.

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 Verilog

Verwundbar Verilog 
assign addr_auth = (address == 32'hF00) ? 1: 0;
Sicheres Codebeispiel

Secure Verilog

The bugged line of code is repeated in the Bad example above. The weakness arises from the fact that the SECURE_ME register can be modified by writing to the shadow register COPY_OF_SECURE_ME. The address of COPY_OF_SECURE_ME should also be included in the check. That buggy line of code should instead be replaced as shown in the Good Code Snippet below.

Sicher Verilog 
assign addr_auth = (address == 32'hF00 || address == 32'h800F00) ? 1: 0;
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-420

  • Architecture and Design Identify all alternate channels and use the same protection mechanisms that are used for the primary channels.
Erkennungssignale

How to detect CWE-420

SAST High

Führe statische Analyse (SAST) auf der Codebasis aus und suche im Datenfluss nach dem unsicheren Muster.

DAST Moderate

Führe dynamische Application-Security-Tests gegen den Live-Endpoint aus.

Runtime Moderate

Beobachte Runtime-Logs auf ungewöhnliche Exception-Traces, fehlerhafte Eingaben oder Versuche, Autorisierung zu umgehen.

Code review Moderate

Code Review: Markiere jeden neuen Code, der Eingaben von dieser Oberfläche ohne validierte Framework-Helper verarbeitet.

Plexicus Auto-Fix

Plexicus erkennt CWE-420 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-420?

This vulnerability occurs when an application secures its main communication path but leaves a backup or alternative channel with weaker or no protection.

Wie gravierend ist CWE-420?

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-420 betroffen?

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

Wie kann ich CWE-420 verhindern?

Identify all alternate channels and use the same protection mechanisms that are used for the primary channels.

Wie erkennt und behebt Plexicus CWE-420?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-420 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-420?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/420.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-420

CWE-923 Parent

Improper Restriction of Communication Channel to Intended Endpoints

This vulnerability occurs when a system opens a communication channel for a sensitive task but fails to properly verify that it's actually…

CWE-1275 Sibling

Sensitive Cookie with Improper SameSite Attribute

This vulnerability occurs when a sensitive cookie does not have a secure SameSite attribute configured, leaving it exposed to cross-site…

CWE-291 Sibling

Reliance on IP Address for Authentication

This vulnerability occurs when a system uses a client's IP address as the sole or primary method to verify their identity.

CWE-297 Sibling

Improper Validation of Certificate with Host Mismatch

This vulnerability occurs when an application accepts a valid SSL/TLS certificate without properly verifying that it actually belongs to…

CWE-300 Sibling

Channel Accessible by Non-Endpoint

This vulnerability occurs when a system fails to properly verify who is on the other end of a communication link or to secure the channel…

CWE-419 Sibling

Unprotected Primary Channel

This vulnerability occurs when an application exposes a privileged administrative interface or restricted functionality through a primary…

CWE-940 Sibling

Improper Verification of Source of a Communication Channel

This vulnerability occurs when an application accepts incoming communication requests without properly checking where they originate from,…

CWE-941 Sibling

Incorrectly Specified Destination in a Communication Channel

This vulnerability occurs when an application establishes an outgoing communication channel but fails to correctly define or enforce the…

CWE-942 Sibling

Permissive Cross-domain Security Policy with Untrusted Domains

This vulnerability occurs when a web application's cross-domain security policy, like a Content Security Policy (CSP), explicitly allows…

Ressourcen

Further reading

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