CWE-181 Detail

CWE-181

Incorrect Behavior Order: Validate Before Filter
Draft
2006-07-19
00h00 +00:00
2023-06-29
00h00 +00:00
CWE Mitre.org
Notifications for a CWE
Stay informed of any changes for a specific CWE.
Notifications manage

Name: Incorrect Behavior Order: Validate Before Filter

The product validates data before it has been filtered, which prevents the product from detecting data that becomes invalid after the filtering step.

CWE Description

This can be used by an attacker to bypass the validation and launch attacks that expose weaknesses that would otherwise be prevented, such as injection.

General Informations

Modes Of Introduction

Implementation

Applicable Platforms

Language

Class: Not Language-Specific (Undetermined)

Common Consequences

Scope Impact Likelihood
Access ControlBypass Protection Mechanism

Observed Examples

References Description

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.

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.

Potential Mitigations

Phases : Implementation // Architecture and Design
Inputs should be decoded and canonicalized to the application's current internal representation before being filtered.

Vulnerability Mapping Notes

Justification : This CWE entry is at the Variant level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comment : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Related Attack Patterns

CAPEC-ID Attack Pattern Name
CAPEC-120 Double Encoding
The adversary utilizes a repeating of the encoding process for a set of characters (that is, character encoding a character encoding of a character) to obfuscate the payload of a particular request. This may allow the adversary to bypass filters that attempt to detect illegal characters or strings, such as those that might be used in traversal or injection attacks. Filters may be able to catch illegal encoded strings, but may not catch doubly encoded strings. For example, a dot (.), often used in path traversal attacks and therefore often blocked by filters, could be URL encoded as %2E. However, many filters recognize this encoding and would still block the request. In a double encoding, the % in the above URL encoding would be encoded again as %25, resulting in %252E which some filters might not catch, but which could still be interpreted as a dot (.) by interpreters on the target.
CAPEC-267 Leverage Alternate Encoding
An adversary leverages the possibility to encode potentially harmful input or content used by applications such that the applications are ineffective at validating this encoding standard.
CAPEC-3 Using Leading 'Ghost' Character Sequences to Bypass Input Filters
Some APIs will strip certain leading characters from a string of parameters. An adversary can intentionally introduce leading "ghost" characters (extra characters that don't affect the validity of the request at the API layer) that enable the input to pass the filters and therefore process the adversary's input. This occurs when the targeted API will accept input data in several syntactic forms and interpret it in the equivalent semantic way, while the filter does not take into account the full spectrum of the syntactic forms acceptable to the targeted API.
CAPEC-43 Exploiting Multiple Input Interpretation Layers
An attacker supplies the target software with input data that contains sequences of special characters designed to bypass input validation logic. This exploit relies on the target making multiples passes over the input data and processing a "layer" of special characters with each pass. In this manner, the attacker can disguise input that would otherwise be rejected as invalid by concealing it with layers of special/escape characters that are stripped off by subsequent processing steps. The goal is to first discover cases where the input validation layer executes before one or more parsing layers. That is, user input may go through the following logic in an application: --> --> . In such cases, the attacker will need to provide input that will pass through the input validator, but after passing through parser2, will be converted into something that the input validator was supposed to stop.
CAPEC-78 Using Escaped Slashes in Alternate Encoding
This attack targets the use of the backslash in alternate encoding. An adversary can provide a backslash as a leading character and causes a parser to believe that the next character is special. This is called an escape. By using that trick, the adversary tries to exploit alternate ways to encode the same character which leads to filter problems and opens avenues to attack.
CAPEC-79 Using Slashes in Alternate Encoding
This attack targets the encoding of the Slash characters. An adversary would try to exploit common filtering problems related to the use of the slashes characters to gain access to resources on the target host. Directory-driven systems, such as file systems and databases, typically use the slash character to indicate traversal between directories or other container components. For murky historical reasons, PCs (and, as a result, Microsoft OSs) choose to use a backslash, whereas the UNIX world typically makes use of the forward slash. The schizophrenic result is that many MS-based systems are required to understand both forms of the slash. This gives the adversary many opportunities to discover and abuse a number of common filtering problems. The goal of this pattern is to discover server software that only applies filters to one version, but not the other.
CAPEC-80 Using UTF-8 Encoding to Bypass Validation Logic
This attack is a specific variation on leveraging alternate encodings to bypass validation logic. This attack leverages the possibility to encode potentially harmful input in UTF-8 and submit it to applications not expecting or effective at validating this encoding standard making input filtering difficult. UTF-8 (8-bit UCS/Unicode Transformation Format) is a variable-length character encoding for Unicode. Legal UTF-8 characters are one to four bytes long. However, early version of the UTF-8 specification got some entries wrong (in some cases it permitted overlong characters). UTF-8 encoders are supposed to use the "shortest possible" encoding, but naive decoders may accept encodings that are longer than necessary. According to the RFC 3629, a particularly subtle form of this attack can be carried out against a parser which performs security-critical validity checks against the UTF-8 encoded form of its input, but interprets certain illegal octet sequences as characters.

NotesNotes

This category is probably under-studied.

Submission

Name Organization Date Date release Version
PLOVER 2006-07-19 +00:00 2006-07-19 +00:00 Draft 3

Modifications

Name Organization Date Comment
Eric Dalci Cigital 2008-07-01 +00:00 updated Potential_Mitigations, Time_of_Introduction
Veracode 2008-08-15 +00:00 Suggested OWASP Top Ten 2004 mapping
CWE Content Team MITRE 2008-09-08 +00:00 updated Functional_Areas, Relationships, Research_Gaps, Taxonomy_Mappings, Type
CWE Content Team MITRE 2008-10-14 +00:00 updated Description
CWE Content Team MITRE 2010-06-21 +00:00 updated Description, Observed_Examples
CWE Content Team MITRE 2011-03-29 +00:00 updated Demonstrative_Examples
CWE Content Team MITRE 2011-06-01 +00:00 updated Common_Consequences
CWE Content Team MITRE 2012-05-11 +00:00 updated Demonstrative_Examples, Observed_Examples, Related_Attack_Patterns, Relationships
CWE Content Team MITRE 2012-10-30 +00:00 updated Potential_Mitigations
CWE Content Team MITRE 2014-07-30 +00:00 updated Relationships
CWE Content Team MITRE 2017-01-19 +00:00 updated Relationships
CWE Content Team MITRE 2017-11-08 +00:00 updated Applicable_Platforms
CWE Content Team MITRE 2019-01-03 +00:00 updated Related_Attack_Patterns
CWE Content Team MITRE 2020-02-24 +00:00 updated Relationships, Type
CWE Content Team MITRE 2023-01-31 +00:00 updated Description
CWE Content Team MITRE 2023-04-27 +00:00 updated Relationships
CWE Content Team MITRE 2023-06-29 +00:00 updated Mapping_Notes