CWE-212: Improper Cross-boundary Removal of Sensitive Data
Improper Cross-boundary Removal of Sensitive Data
Weakness ID: 212 (Weakness Base)
Status: Incomplete
Description
Description Summary
The software uses a resource that contains sensitive data, but it does not properly remove that data before it stores, transfers, or shares the resource with actors in another control sphere.
Extended Description
Resources that may contain sensitive data include documents, packets, messages, databases, etc. While this data may be useful to an individual user or small set of users who share the resource, it may need to be removed before the resource can be shared outside of the trusted group. The process of removal is sometimes called cleansing or scrubbing.
For example, software that is used for editing documents might not remove sensitive data such as reviewer comments or the local pathname where the document is stored. Or, a proxy might not remove an internal IP address from headers before making an outgoing request to an Internet site.
Terminology Notes
The terms "cleansing" and "scrubbing" have multiple uses within computing.
In information security, these are used for the removal of sensitive data,
but they are also used for the modification of incoming/outgoing data so
that it conforms to specifications.
Time of Introduction
Architecture and Design
Implementation
Operation
Applicable Platforms
Languages
Language-independent
Common Consequences
Scope
Effect
Confidentiality
Technical Impact: Read files or
directories; Read application
data
Sensitive data may be exposed to an unauthorized actor in another
control sphere. This may have a wide range of secondary consequences
which will depend on what data is exposed. One possibility is the
exposure of system data allowing an attacker to craft a specific, more
effective attack.
Demonstrative Examples
Example 1
This code either generates a public HTML user information page or a
JSON response containing the same user information.
(Bad Code)
Example
Language: PHP
// API flag, output JSON if set
$json = $_GET['json']
$username = $_GET['user']
if(!$json)
{
$record = getUserRecord($username);
foreach($record as $fieldName => $fieldValue)
{
if($fieldName == "email_address") {
// skip displaying user emails
continue;
}
else{
writeToHtmlPage($fieldName,$fieldValue);
}
}
}
else
{
$record = getUserRecord($username);
echo json_encode($record);
}
The programmer is careful to not display the user's e-mail address
when displaying the public HTML page. However, the e-mail address is not
removed from the JSON response, exposing the user's e-mail address.
NAT feature in firewall leaks internal IP
addresses in ICMP error messages.
Potential Mitigations
Phase: Requirements
Clearly specify which information should be regarded as private or
sensitive, and require that the product offers functionality that allows
the user to cleanse the sensitive information from the resource before
it is published or exported to other parties.
Phase: Architecture and Design
Strategy: Separation of Privilege
Compartmentalize the system to have "safe" areas where trust
boundaries can be unambiguously drawn. Do not allow sensitive data to go
outside of the trust boundary and always be careful when interfacing
with a compartment outside of the safe area.
Ensure that appropriate compartmentalization is built into the system
design and that the compartmentalization serves to allow for and further
reinforce privilege separation functionality. Architects and designers
should rely on the principle of least privilege to decide when it is
appropriate to use and to drop system privileges.
Phase: Implementation
Strategy: Identify and Reduce Attack Surface
Use naming conventions and strong types to make it easier to spot when
sensitive data is being used. When creating structures, objects, or
other complex entities, separate the sensitive and non-sensitive data as
much as possible.
Effectiveness: Defense in Depth
This makes it easier to spot places in the code where data is being
used that is unencrypted.
Phase: Implementation
Avoid errors related to improper resource shutdown or release (CWE-404), which may leave the sensitive data within the resource if it is in an incomplete state.
This entry is intended to be different from resultant information leaks,
including those that occur from improper buffer initialization and reuse,
improper encryption, interaction errors, and multiple interpretation errors.
This entry could be regarded as a privacy leak, depending on the type of
information that is leaked.
There is a close association between CWE-226 and CWE-212. The difference is partially that of perspective. CWE-226 is geared towards the final stage of the resource lifecycle, in which the resource is deleted, eliminated, expired, or otherwise released for reuse. Technically, this involves a transfer to a different control sphere, in which the original contents of the resource are no longer relevant. CWE-212, however, is intended for sensitive data in resources that are intentionally shared with others, so they are still active. This distinction is useful from the perspective of the CWE research view (CWE-1000).
Description
