Improper Control of Filename for Include/Require Statement in PHP Program ('PHP File Inclusion')
|ID: 98||Date: (C)2012-05-14 (M)2012-11-08|
|Type: weakness||Status: DRAFT|
|Abstraction Type: Base|
The PHP application receives input from an upstream component,
but it does not restrict or incorrectly restricts the input before its usage in
"require," "include," or similar functions.
Extended DescriptionIn certain versions and configurations of PHP, this can allow an attacker
to specify a URL to a remote location from which the software will obtain
the code to execute. In other cases in association with path traversal, the
attacker can specify a local file that may contain executable statements
that can be parsed by PHP.
Likelihood of Exploit: High to Very High
Applicable PlatformsLanguage: OftenLanguage: PHP
Time Of Introduction
- Architecture and Design
Related Attack Patterns
|IntegrityConfidentialityAvailability ||Execute unauthorized code or
commands ||The attacker may be able to specify arbitrary code to be executed from
a remote location. Alternatively, it may be possible to use normal
program behavior to insert php code into files on the local machine
which can then be included and force the code to execute since php
ignores everything in the file except for the content between php
|Manual Analysis ||Manual white-box analysis can be very effective for finding this
issue, since there is typically a relatively small number of include or
require statements in each program. ||High || |
|Automated Static Analysis ||The external control or influence of filenames can often be detected
using automated static analysis that models data flow within the
software.Automated static analysis might not be able to recognize when proper
input validation is being performed, leading to false positives - i.e.,
warnings that do not have any security consequences or require any code
changes. If the program uses a customized input validation library, then
some tools may allow the analyst to create custom signatures to detect
usage of those routines. || || |
|Architecture and Design ||Libraries or Frameworks ||Use a vetted library or framework that does not allow this weakness to
occur or provides constructs that make this weakness easier to
avoid. || || |
|Architecture and Design ||Enforcement by Conversion ||When the set of acceptable objects, such as filenames or URLs, is
limited or known, create a mapping from a set of fixed input values
(such as numeric IDs) to the actual filenames or URLs, and reject all
other inputs.For example, ID 1 could map to "inbox.txt" and ID 2 could map to
"profile.txt". Features such as the ESAPI AccessReferenceMap [R.98.1]
provide this capability. || || |
|Architecture and Design || ||For any security checks that are performed on the client side, ensure
that these checks are duplicated on the server side, in order to avoid
CWE-602. Attackers can bypass the client-side checks by modifying values
after the checks have been performed, or by changing the client to
remove the client-side checks entirely. Then, these modified values
would be submitted to the server. || || |
|Architecture and DesignOperation ||Sandbox or Jail ||Run the code in a "jail" or similar sandbox environment that enforces
strict boundaries between the process and the operating system. This may
effectively restrict which files can be accessed in a particular
directory or which commands can be executed by the software.OS-level examples include the Unix chroot jail, AppArmor, and SELinux.
In general, managed code may provide some protection. For example,
java.io.FilePermission in the Java SecurityManager allows the software
to specify restrictions on file operations.This may not be a feasible solution, and it only limits the impact to
the operating system; the rest of the application may still be subject
to compromise.Be careful to avoid CWE-243 and other weaknesses related to jails. ||Limited ||The effectiveness of this mitigation depends on the prevention
capabilities of the specific sandbox or jail being used and might only
help to reduce the scope of an attack, such as restricting the attacker
to certain system calls or limiting the portion of the file system that
can be accessed. |
|Architecture and DesignOperation ||Environment Hardening ||Run your code using the lowest privileges that are required to
accomplish the necessary tasks [R.98.2]. If possible, create isolated
accounts with limited privileges that are only used for a single task.
That way, a successful attack will not immediately give the attacker
access to the rest of the software or its environment. For example,
database applications rarely need to run as the database administrator,
especially in day-to-day operations. || || |
|Implementation ||Input Validation ||Assume all input is malicious. Use an "accept known good" input
validation strategy, i.e., use a whitelist 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
(i.e., do not rely on a blacklist). A blacklist 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, blacklists can be useful for detecting potential
attacks or determining which inputs are so malformed that they should be
rejected outright.When validating filenames, use stringent whitelists that limit the
character set to be used. If feasible, only allow a single "." character
in the filename to avoid weaknesses such as CWE-23, and exclude
directory separators such as "/" to avoid CWE-36. Use a whitelist of
allowable file extensions, which will help to avoid CWE-434.Do not rely exclusively on a filtering mechanism that removes
potentially dangerous characters. This is equivalent to a blacklist,
which may be incomplete (CWE-184). For example, filtering "/" is
insufficient protection if the filesystem also supports the use of "\"
as a directory separator. Another possible error could occur when the
filtering is applied in a way that still produces dangerous data
(CWE-182). For example, if "../" sequences are removed from the
".../...//" string in a sequential fashion, two instances of "../" would
be removed from the original string, but the remaining characters would
still form the "../" string. || || |
|Architecture and DesignOperation ||Identify and Reduce Attack Surface ||Store library, include, and utility files outside of the web document
root, if possible. Otherwise, store them in a separate directory and use
the web server's access control capabilities to prevent attackers from
directly requesting them. One common practice is to define a fixed
constant in each calling program, then check for the existence of the
constant in the library/include file; if the constant does not exist,
then the file was directly requested, and it can exit
immediately.This significantly reduces the chance of an attacker being able to
bypass any protection mechanisms that are in the base program but not in
the include files. It will also reduce the attack surface. || || |
|Architecture and DesignImplementation ||Identify and Reduce Attack Surface ||Understand all the potential areas where untrusted inputs can enter
your software: parameters or arguments, cookies, anything read from the
network, environment variables, reverse DNS lookups, query results,
request headers, URL components, e-mail, files, filenames, databases,
and any external systems that provide data to the application. Remember
that such inputs may be obtained indirectly through API calls.Many file inclusion problems occur because the programmer assumed that
certain inputs could not be modified, especially for cookies and URL
components. || || |
|Operation ||Firewall ||Use an application firewall that can detect attacks against this
weakness. It can be beneficial in cases in which the code cannot be
fixed (because it is controlled by a third party), as an emergency
prevention measure while more comprehensive software assurance measures
are applied, or to provide defense in depth. ||Moderate ||An application firewall might not cover all possible input vectors. In
addition, attack techniques might be available to bypass the protection
mechanism, such as using malformed inputs that can still be processed by
the component that receives those inputs. Depending on functionality, an
application firewall might inadvertently reject or modify legitimate
requests. Finally, some manual effort may be required for
|OperationImplementation ||Environment Hardening ||Develop and run your code in the most recent versions of PHP
available, preferably PHP 6 or later. Many of the highly risky features
in earlier PHP interpreters have been removed, restricted, or disabled
by default. || || |
|OperationImplementation ||Environment Hardening ||When using PHP, configure the application so that it does not use
register_globals. During implementation, develop the application so that
it does not rely on this feature, but be wary of implementing a
register_globals emulation that is subject to weaknesses such as CWE-95,
CWE-621, and similar issues.Often, programmers do not protect direct access to files intended only
to be included by core programs. These include files may assume that
critical variables have already been initialized by the calling program.
As a result, the use of register_globals combined with the ability to
directly access the include file may allow attackers to conduct file
inclusion attacks. This remains an extremely common pattern as of
2009. || || |
|Operation ||Environment Hardening ||Set allow_url_fopen to false, which limits the ability to include
files from remote locations. ||High ||Be aware that some versions of PHP will still accept ftp:// and other
URI schemes. In addition, this setting does not protect the code from
path traversal attacks (CWE-22), which are frequently successful against
the same vulnerable code that allows remote file inclusion. |
RelationshipsThis is frequently a functional consequence of other weaknesses. It is
usually multi-factor with other factors (e.g. MAID), although not all
inclusion bugs involve assumed-immutable data. Direct request weaknesses
frequently play a role.Can overlap directory traversal in local inclusion problems.
|CWE-98 ChildOf CWE-727 ||Category ||CWE-711 || |
Demonstrative Examples (Details)
- The following code attempts to include a function contained in a
separate PHP page on the server. It builds the path to the file by using the
supplied 'module_name' parameter and appending the string '/function.php' to
- CVE-2004-0285 : Modification of assumed-immutable configuration variable in include file allows file inclusion via direct request.
- CVE-2004-0030 : Modification of assumed-immutable configuration variable in include file allows file inclusion via direct request.
- CVE-2004-0068 : Modification of assumed-immutable configuration variable in include file allows file inclusion via direct request.
- CVE-2005-2157 : Modification of assumed-immutable configuration variable in include file allows file inclusion via direct request.
- CVE-2005-2162 : Modification of assumed-immutable configuration variable in include file allows file inclusion via direct request.
- CVE-2005-2198 : Modification of assumed-immutable configuration variable in include file allows file inclusion via direct request.
- CVE-2004-0128 : Modification of assumed-immutable variable in configuration script leads to file inclusion.
- CVE-2005-1864 : PHP file inclusion.
- CVE-2005-1869 : PHP file inclusion.
- CVE-2005-1870 : PHP file inclusion.
- CVE-2005-2154 : PHP local file inclusion.
- CVE-2002-1704 : PHP remote file include.
- CVE-2002-1707 : PHP remote file include.
- CVE-2005-1964 : PHP remote file include.
- CVE-2005-1681 : PHP remote file include.
- CVE-2005-2086 : PHP remote file include.
- CVE-2004-0127 : Directory traversal vulnerability in PHP include statement.
- CVE-2005-1971 : Directory traversal vulnerability in PHP include statement.
- CVE-2005-3335 : PHP file inclusion issue, both remote and local; local include uses ".." and "%00" characters as a manipulation, but many remote file inclusion issues probably have this vector.
For more examples, refer to CVE relations in the bottom box.
White Box Definitions None
Black Box Definitions None
|PLOVER || ||PHP File Include || |
|OWASP Top Ten 2007 ||A3 ||Malicious File Execution ||CWE_More_Specific |
|WASC ||5 ||Remote File Inclusion || |
- OWASP .Testing for Path Traversal (OWASP-AZ-001).
- Sean Barnum Michael Gegick .Least Privilege. Published on 2005-09-14.
- Shaun Clowes .A Study in Scarlet.
- Stefan Esser .Suhosin.
- Johannes Ullrich .Top 25 Series - Rank 13 - PHP File Inclusion. SANS Software Security Institute. 2010-03-11.