Détail du CWE-177

CWE-177

Improper Handling of URL Encoding (Hex Encoding)
Draft
2006-07-19
00h00 +00:00
2023-06-29
00h00 +00:00
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Nom: Improper Handling of URL Encoding (Hex Encoding)

The product does not properly handle when all or part of an input has been URL encoded.

Informations générales

Modes d'introduction

Implementation

Plateformes applicables

Langue

Class: Not Language-Specific (Undetermined)

Conséquences courantes

Portée Impact Probabilité
IntegrityUnexpected State

Exemples observés

Références Description

CVE-2000-0900

Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e"

CVE-2005-2256

Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e"

CVE-2004-2121

Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e"

CVE-2004-0280

"%20" (encoded space)

CVE-2003-0424

"%20" (encoded space)

CVE-2001-0693

"%20" (encoded space)

CVE-2001-0778

"%20" (encoded space)

CVE-2002-1831

Crash via hex-encoded space "%20".

CVE-2000-0671

"%00" (encoded null)

CVE-2004-0189

"%00" (encoded null)

CVE-2002-1291

"%00" (encoded null)

CVE-2002-1031

"%00" (encoded null)

CVE-2001-1140

"%00" (encoded null)

CVE-2004-0760

"%00" (encoded null)

CVE-2002-1025

"%00" (encoded null)

CVE-2002-1213

"%2f" (encoded slash)

CVE-2004-0072

"%5c" (encoded backslash) and "%2e" (encoded dot) sequences

CVE-2004-0847

"%5c" (encoded backslash)

CVE-2002-1575

"%0a" (overlaps CRLF)

Mesures d’atténuation potentielles

Phases : Architecture and Design
Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.
Phases : Implementation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."

Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.


Phases : 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.

Notes de cartographie des vulnérabilités

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.
Commentaire : 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.

Modèles d'attaque associés

CAPEC-ID Nom du modèle d'attaque
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-468 Generic Cross-Browser Cross-Domain Theft
An attacker makes use of Cascading Style Sheets (CSS) injection to steal data cross domain from the victim's browser. The attack works by abusing the standards relating to loading of CSS: 1. Send cookies on any load of CSS (including cross-domain) 2. When parsing returned CSS ignore all data that does not make sense before a valid CSS descriptor is found by the CSS parser.
CAPEC-64 Using Slashes and URL Encoding Combined to Bypass Validation Logic
This attack targets the encoding of the URL combined with the encoding of the slash characters. An attacker can take advantage of the multiple ways of encoding a URL and abuse the interpretation of the URL. A URL may contain special character that need special syntax handling in order to be interpreted. Special characters are represented using a percentage character followed by two digits representing the octet code of the original character (%HEX-CODE). For instance US-ASCII space character would be represented with %20. This is often referred as escaped ending or percent-encoding. Since the server decodes the URL from the requests, it may restrict the access to some URL paths by validating and filtering out the URL requests it received. An attacker will try to craft an URL with a sequence of special characters which once interpreted by the server will be equivalent to a forbidden URL. It can be difficult to protect against this attack since the URL can contain other format of encoding such as UTF-8 encoding, Unicode-encoding, etc.
CAPEC-72 URL Encoding
This attack targets the encoding of the URL. An adversary can take advantage of the multiple way of encoding an URL and abuse the interpretation of the URL.

Soumission

Nom Organisation Date Date de publication Version
PLOVER 2006-07-19 +00:00 2006-07-19 +00:00 Draft 3

Modifications

Nom Organisation Date Commentaire
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 Relationships, Observed_Example, Taxonomy_Mappings
CWE Content Team MITRE 2009-07-27 +00:00 updated Potential_Mitigations
CWE Content Team MITRE 2010-12-13 +00:00 updated Name
CWE Content Team MITRE 2011-03-29 +00:00 updated Potential_Mitigations
CWE Content Team MITRE 2011-06-01 +00:00 updated Common_Consequences
CWE Content Team MITRE 2011-06-27 +00:00 updated Common_Consequences
CWE Content Team MITRE 2012-05-11 +00:00 updated 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 2017-11-08 +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 Potential_Mitigations, Relationships
CWE Content Team MITRE 2020-06-25 +00:00 updated Potential_Mitigations
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