Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection')
|ID: 95||Date: (C)2012-05-14 (M)2012-11-08|
|Type: weakness||Status: INCOMPLETE|
|Abstraction Type: Base|
The software receives input from an upstream component, but it
does not neutralize or incorrectly neutralizes code syntax before using the
input in a dynamic evaluation call (e.g. "eval").
Extended DescriptionThis may allow an attacker to execute arbitrary code, or at least modify
what code can be executed.
Likelihood of Exploit: Medium
Time Of Introduction
- Architecture and Design
Related Attack Patterns
|Confidentiality ||Read files or
data ||The injected code could access restricted data / files. |
|Access_Control ||Bypass protection
mechanism ||In some cases, injectable code controls authentication; this may lead
to a remote vulnerability. |
|Access_Control ||Gain privileges / assume
identity ||Injected code can access resources that the attacker is directly
prevented from accessing. |
|IntegrityConfidentialityAvailabilityOther ||Execute unauthorized code or
commands ||Code injection attacks can lead to loss of data integrity in nearly
all cases as the control-plane data injected is always incidental to
data recall or writing. Additionally, code injection can often result in
the execution of arbitrary code. |
|Non-Repudiation ||Hide activities ||Often the actions performed by injected control code are
|Architecture and DesignImplementation || ||If possible, refactor your code so that it does not need to use eval()
at all. || || |
|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. || || |
|Implementation || ||Inputs should be decoded and canonicalized to the application's
current internal representation before being validated (CWE-180,
CWE-181). Make sure that your application does not inadvertently decode
the same input twice (CWE-174). Such errors could be used to bypass
whitelist schemes by introducing dangerous inputs after they have been
checked. Use libraries such as the OWASP ESAPI Canonicalization
control.Consider performing repeated canonicalization until your input does
not change any more. This will avoid double-decoding and similar
scenarios, but it might inadvertently modify inputs that are allowed to
contain properly-encoded dangerous content. || || |
|CWE-95 ChildOf CWE-896 ||Category ||CWE-888 || |
Demonstrative Examples (Details)
- edit-config.pl: This CGI script is used to modify settings in a
configuration file. (Demonstrative Example Id DX-31)
- CVE-2008-5071 : Eval injection in PHP program.
- CVE-2002-1750 : Eval injection in Perl program.
- CVE-2008-5305 : Eval injection in Perl program using an ID that should only contain hyphens and numbers.
- CVE-2002-1752 : Direct code injection into Perl eval function.
- CVE-2002-1753 : Eval injection in Perl program.
- CVE-2005-1527 : Direct code injection into Perl eval function.
- CVE-2005-2837 : Direct code injection into Perl eval function.
- CVE-2005-1921 : MFV. code injection into PHP eval statement using nested constructs that should not be nested.
- CVE-2005-2498 : MFV. code injection into PHP eval statement using nested constructs that should not be nested.
- CVE-2005-3302 : Code injection into Python eval statement from a field in a formatted file.
- CVE-2007-1253 : Eval injection in Python program.
- CVE-2001-1471 : chain: Resultant eval injection. An invalid value prevents initialization of variables, which can be modified by attacker and later injected into PHP eval statement.
For more examples, refer to CVE relations in the bottom box.
White Box Definitions None
Black Box Definitions None
|PLOVER || ||Direct Dynamic Code Evaluation ('Eval
Injection') || |
|OWASP Top Ten 2007 ||A3 ||Malicious File Execution ||CWE_More_Specific |
|OWASP Top Ten 2004 ||A6 ||Injection Flaws ||CWE_More_Specific |
- Mark Dowd John McDonald Justin Schuh .The Art of Software Security Assessment 1st Edition. Addison Wesley. Section:'Chapter 18, "Inline Evaluation", Page
1095.'. Published on 2006.