Vulnerability Mapping:ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities Abstraction:
BaseBase - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
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Description
The product accepts XML from an untrusted source but does not validate the XML against the proper schema.
Common Consequences
This table specifies different individual consequences
associated with the weakness. The Scope identifies the application security area that is
violated, while the Impact describes the negative technical impact that arises if an
adversary succeeds in exploiting this weakness. The Likelihood provides information about
how likely the specific consequence is expected to be seen relative to the other
consequences in the list. For example, there may be high likelihood that a weakness will be
exploited to achieve a certain impact, but a low likelihood that it will be exploited to
achieve a different impact.
Impact
Details
Unexpected State; Varies by Context
Scope: Integrity
By accepting an XML document without validating it against a DTD or XML schema, the programmer leaves a door open for attackers to provide unexpected, unreasonable, or malicious input.
Potential Mitigations
Phase(s)
Mitigation
Architecture and Design
Strategy: Input Validation
Always validate XML input against a known XML Schema or DTD.
It is not possible for an XML parser to validate all aspects of a document's content because a parser cannot understand the complete semantics of the data. However, a parser can do a complete and thorough job of checking the document's structure and therefore guarantee to the code that processes the document that the content is well-formed.
Relationships
This table shows the weaknesses and high level categories that are related to this
weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to
similar items that may exist at higher and lower levels of abstraction. In addition,
relationships such as PeerOf, Overlaps, and CanAlsoBe are defined to show similar weaknesses that the user
may want to explore.
Relevant to the view "Complete Weakness Hierarchy" (View-1000)
Nature
Type
ID
Name
ChildOf
Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
Relevant to the view "Seven Pernicious Kingdoms" (View-700)
Nature
Type
ID
Name
ChildOf
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
The different Modes of Introduction provide information
about how and when this
weakness may be introduced. The Phase identifies a point in the life cycle at which
introduction
may occur, while the Note provides a typical scenario related to introduction during the
given
phase.
Phase(s)
Note
Implementation
The programmer might assume that a provided XML document is well-formed.
Applicable Platforms
This listing shows possible areas for which the given
weakness could appear. These
may be for specific named Languages, Operating Systems, Architectures, Paradigms,
Technologies,
or a class of such platforms. The platform is listed along with how frequently the given
weakness appears for that instance.
Type
Applicable Platforms
Notes
Languages
Class: Not Language-Specific
(Undetermined Prevalence)
The DocumentBuilder object does not validate an XML document against a schema, making it possible to create an invalid XML document.
Example 3
The following PHP code receives XML content from an HTTP request body,
loads the XML content into a PHP SimpleXMLElement Object ($xml), and prints
the results back to the user.
(bad code)
Example Language: PHP
$xmlContent = file_get_contents('php://input');
if (empty($xmlContent)) {
http_response_code(400);
exit('No XML content received.');
The above PHP code is vulnerable because it directly loads XML from
user-controlled input. It might assume that the XML is already
compliant with the schema. According to PHP documentation,
simplexml_load_string() only assumes a "well-formed XML
string" [REF-1551]. So, the code does not actually validate its
structure against a schema (XSD) or a Document Type Definition (DTD).
If the XML does not comply with the expected schema, this lack of
validation could result in the application processing and handling
malformed or unexpected data.
A separate validation step can ensure that any provided data is valid
with respect to the expected XSD/DTD, to address CWE-112.
(good code)
Example Language: PHP
$xmlContent = file_get_contents('php://input');
// We skip a check that $xmlContent is empty
// Disable external entity loading to prevent XXE
libxml_disable_entity_loader(true);
libxml_use_internal_errors(true);
$dom = new DOMDocument();
$dom->loadXML($xmlString, LIBXML_NONET);
if (!$dom->schemaValidate('/xml/schema.xsd')) {
http_response_code(400);
exit('Invalid XML file.');
}
echo $dom->saveXML();
Note that the validation step in this code could be inefficient if it
is only applied to inherently trusted files, but there are some
scenarios in which an application must accept externally-submitted
XML. In such cases, the schema validation could occur at an earlier
step.
Weakness Ordinalities
Ordinality
Description
Primary
(where the weakness exists independent of other weaknesses)
Detection
Methods
Method
Details
Automated Static Analysis
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
Effectiveness: High
Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that
reference this weakness as a member. This information is often useful in understanding where a
weakness fits within the context of external information sources.
Nature
Type
ID
Name
MemberOf
Grouping - a CWE entry that contains a set of other entries that share a common characteristic.
(this CWE ID may be used to map to real-world vulnerabilities)
Reason
Acceptable-Use
Rationale
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comments
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.
Katrina Tsipenyuk, Brian Chess and Gary McGraw. "Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors". NIST Workshop on Software Security Assurance Tools Techniques and Metrics. NIST. 2005-11-07.
<https://cwe.mitre.org/documents/sources/SevenPerniciousKingdoms.pdf>.
Description
This table specifies different individual consequences
associated with the weakness. The Scope identifies the application security area that is
violated, while the Impact describes the negative technical impact that arises if an
adversary succeeds in exploiting this weakness. The Likelihood provides information about
how likely the specific consequence is expected to be seen relative to the other
consequences in the list. For example, there may be high likelihood that a weakness will be
exploited to achieve a certain impact, but a low likelihood that it will be exploited to
achieve a different impact.
