CWE

Incorrect Behavior Order: Early Validation

ID: 179		Date: (C)2012-05-14   (M)2022-10-10
Type: weakness		Status: INCOMPLETE
Abstraction Type: Base

Description

The software validates input before applying protection mechanisms that modify the input, which could allow an attacker to bypass the validation via dangerous inputs that only arise after the modification.

Extended Description

Software needs to validate data at the proper time, after data has been canonicalized and cleansed. Early validation is susceptible to various manipulations that result in dangerous inputs that are produced by canonicalization and cleansing.

Applicable Platforms
Language Class: All

Time Of Introduction

• Implementation

Related Attack Patterns

• CAPEC-3
• CAPEC-43
• CAPEC-71

Common Consequences

Scope	Technical Impact	Notes
Access_Control Integrity	Bypass protection mechanism Execute unauthorized code or commands	An attacker could include dangerous input that bypasses validation protection mechanisms which can be used to launch various attacks including injection attacks, execute arbitrary code or cause other unintended behavior.

Detection Methods
None

Potential Mitigations

Phase	Strategy	Description	Effectiveness	Notes
Implementation	Input Validation	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 whitelist validation schemes by introducing dangerous inputs after they have been checked.

Relationships

Related CWE	Type	View	Chain
CWE-179 ChildOf CWE-896	Category	CWE-888

Demonstrative Examples   (Details)

1. The following code attempts to validate a given input path by checking it against a whitelist and then return the canonical path. In this specific case, the path is considered valid if it starts with the string "/safe_dir/". (Demonstrative Example Id DX-35)
2. This script creates a subdirectory within a user directory and sets the user as the owner. (Demonstrative Example Id DX-36)

Observed Examples

1. CVE-2002-0433 : Product allows remote attackers to view restricted files via an HTTP request containing a "*" (wildcard or asterisk) character.
2. 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.
3. 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.
4. CVE-2000-0191 : Overlaps "fakechild/../realchild"
5. 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.
6. CVE-2002-0934 : Directory traversal vulnerability allows remote attackers to read or modify arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a ".." sequence.
7. CVE-2003-0282 : Directory traversal vulnerability allows attackers to overwrite arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a ".." sequence.

For more examples, refer to CVE relations in the bottom box.

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

Taxynomy	Id	Name	Fit
PLOVER		Early Validation Errors

References:

1. Mark Dowd John McDonald Justin Schuh .The Art of Software Security Assessment 1st Edition. Addison Wesley. Section:'Chapter 8, "Escaping Metacharacters", Page 439.'. Published on 2006.