CWE-409 Base Incomplete

Improper Handling of Highly Compressed Data (Data Amplification)

This vulnerability occurs when software fails to safely process highly compressed data, where a small input file can trigger the creation of an extremely large amount of data during decompression,…

Definition

What is CWE-409?

This vulnerability occurs when software fails to safely process highly compressed data, where a small input file can trigger the creation of an extremely large amount of data during decompression, overwhelming system resources.

Often called a 'decompression bomb' or 'zip bomb,' this attack exploits the extreme compression ratios possible with formats like ZIP, XML, or PDF. A malicious actor can craft a tiny, harmless-looking file that, when processed by your application, expands to consume gigabytes of memory or disk space, leading to denial of service, crashes, or performance degradation. To prevent this, developers must implement security controls before decompression. This includes setting strict limits on the compression ratio, checking the uncompressed size from file headers before allocating memory, and using streaming decompression with quotas instead of loading entire outputs into memory at once. Treating all compressed input as untrusted and validating its potential impact is a critical step in secure file handling.

Auswirkungen in der Praxis

Real-world CVEs caused by CWE-409

CVE-2009-1955

XML bomb in web server module
CVE-2003-1564

Parsing library allows XML bomb

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

1
Identifiziere einen Codepfad, der nicht vertrauenswürdige Eingaben ohne Validierung verarbeitet.
2
Erzeuge eine Payload, die das unsichere Verhalten auslöst — Injection, Traversal, Overflow oder Logik-Missbrauch.
3
Liefere die Payload über einen normalen Request aus und beobachte die Reaktion der Anwendung.
4
Iteriere, bis die Antwort Daten preisgibt, Angreifer-Code ausführt oder Berechtigungen eskaliert.

Verwundbares Codebeispiel

Vulnerable XML

The DTD and the very brief XML below illustrate what is meant by an XML bomb. The ZERO entity contains one character, the letter A. The choice of entity name ZERO is being used to indicate length equivalent to that exponent on two, that is, the length of ZERO is 2^0. Similarly, ONE refers to ZERO twice, therefore the XML parser will expand ONE to a length of 2, or 2^1. Ultimately, we reach entity THIRTYTWO, which will expand to 2^32 characters in length, or 4 GB, probably consuming far more data than expected.

Verwundbar XML

<?xml version="1.0"?>
  <!DOCTYPE MaliciousDTD [
  <!ENTITY ZERO "A">
  <!ENTITY ONE "&ZERO;&ZERO;">
  <!ENTITY TWO "&ONE;&ONE;">
  ...
  <!ENTITY THIRTYTWO "&THIRTYONE;&THIRTYONE;">
  ]>
  <data>&THIRTYTWO;</data>

Angreifer-Payload

Angreifer-Payload XML

<?xml version="1.0"?>
  <!DOCTYPE MaliciousDTD [
  <!ENTITY ZERO "A">
  <!ENTITY ONE "&ZERO;&ZERO;">
  <!ENTITY TWO "&ONE;&ONE;">
  ...
  <!ENTITY THIRTYTWO "&THIRTYONE;&THIRTYONE;">
  ]>
  <data>&THIRTYTWO;</data>

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-409

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-409

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-409 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-409?

Wie gravierend ist CWE-409?

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-409 betroffen?

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

Wie kann ich CWE-409 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-409?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-409 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-409?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/409.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-409

CWE-405 Parent

Asymmetric Resource Consumption (Amplification)

This vulnerability occurs when a system allows an attacker to trigger a disproportionate amount of resource consumption—like CPU, memory,…

CWE-1050 Sibling

Excessive Platform Resource Consumption within a Loop

This vulnerability occurs when a loop contains code that repeatedly consumes critical system resources like file handles, database…

CWE-1072 Sibling

Data Resource Access without Use of Connection Pooling

This weakness occurs when an application creates a new database connection for every request instead of using a managed connection pool.…

CWE-1073 Sibling

Non-SQL Invokable Control Element with Excessive Number of Data Resource Accesses

This weakness occurs when a client-side function or method makes an excessive number of individual data requests through a non-SQL data…

CWE-1084 Sibling

Invokable Control Element with Excessive File or Data Access Operations

This weakness occurs when a single function or method performs an excessive number of file or database operations, such as repeated reads,…

CWE-1089 Sibling

Large Data Table with Excessive Number of Indices

This weakness occurs when an application uses a database table with a very large number of rows and creates too many indexes on it,…

CWE-1094 Sibling

Excessive Index Range Scan for a Data Resource

This weakness occurs when a database query performs an index range scan that can access an unnecessarily large number of rows from a…

CWE-1176 Sibling

Inefficient CPU Computation

This weakness occurs when software uses inefficient algorithms or suboptimal CPU operations, performing unnecessary or overly complex…

CWE-406 Sibling

Insufficient Control of Network Message Volume (Network Amplification)

This vulnerability occurs when a system fails to properly limit the amount of network traffic it can generate in response to a request,…

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