CWE-180 Variant Draft

Incorrect Behavior Order: Validate Before Canonicalize

This vulnerability occurs when a system checks user input for malicious content before standardizing its format, allowing specially crafted data to bypass security checks.

Definition

What is CWE-180?

This vulnerability occurs when a system checks user input for malicious content before standardizing its format, allowing specially crafted data to bypass security checks.
When validation runs before canonicalization (the process of converting data into a standard, consistent form), attackers can exploit the gap between these two steps. They can submit input that appears safe during the initial check but transforms into a dangerous payload after it's standardized. For example, an attacker might use alternate character encodings, multiple slashes, or dot sequences that resolve to a forbidden path after canonicalization. This flaw effectively neutralizes security defenses like allow-lists or injection filters, creating a false sense of security. To prevent this, always canonicalize input first—convert it to its simplest, canonical form—and then perform validation and sanitization on that standardized data. This ensures your security logic evaluates the actual data the application will use.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-180

  • CVE-2002-0433

    Product allows remote attackers to view restricted files via an HTTP request containing a "*" (wildcard or asterisk) character.

  • CVE-2003-0332

    Product modifies the first two letters of a filename extension after performing a security check, which allows remote attackers to bypass authentication via a filename with a .ats extension instead of a .hts extension.

  • CVE-2002-0802

    Database consumes an extra character when processing a character that cannot be converted, which could remove an escape character from the query and make the application subject to SQL injection attacks.

  • CVE-2000-0191

    Overlaps "fakechild/../realchild"

  • CVE-2004-2363

    Product checks URI for "<" and other literal characters, but does it before hex decoding the URI, so "%3E" and other sequences are allowed.

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    The following code attempts to validate a given input path by checking it against an allowlist and then return the canonical path. In this specific case, the path is considered valid if it starts with the string "/safe_dir/".

  2. 2

    The problem with the above code is that the validation step occurs before canonicalization occurs. An attacker could provide an input path of "/safe_dir/../" that would pass the validation step. However, the canonicalization process sees the double dot as a traversal to the parent directory and hence when canonicized the path would become just "/".

  3. 3

    To avoid this problem, validation should occur after canonicalization takes place. In this case canonicalization occurs during the initialization of the File object. The code below fixes the issue.

Verwundbares Codebeispiel

Vulnerable Java

The following code attempts to validate a given input path by checking it against an allowlist and then return the canonical path. In this specific case, the path is considered valid if it starts with the string "/safe_dir/".

Verwundbar Java 
String path = getInputPath();
  if (path.startsWith("/safe_dir/"))
  {
  	File f = new File(path);
  	return f.getCanonicalPath();
  }
Sicheres Codebeispiel

Secure Java

To avoid this problem, validation should occur after canonicalization takes place. In this case canonicalization occurs during the initialization of the File object. The code below fixes the issue.

Sicher Java 
String path = getInputPath();
  File f = new File(path);
  if (f.getCanonicalPath().startsWith("/safe_dir/"))
  {
  	return f.getCanonicalPath();
  }
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-180

  • Implementation Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Erkennungssignale

How to detect CWE-180

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-180 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-180?

This vulnerability occurs when a system checks user input for malicious content before standardizing its format, allowing specially crafted data to bypass security checks.

Wie gravierend ist CWE-180?

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-180 betroffen?

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

Wie kann ich CWE-180 verhindern?

Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

Wie erkennt und behebt Plexicus CWE-180?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-180 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-180?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/180.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-180

CWE-179 Parent

Incorrect Behavior Order: Early Validation

This vulnerability occurs when an application validates user input before applying security filters or data normalization. Attackers can…

CWE-181 Sibling

Incorrect Behavior Order: Validate Before Filter

This vulnerability occurs when a system checks user input for validity before cleaning or filtering it. This flawed sequence allows…

Ressourcen

Further reading

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