Improper Control of Generation of Code ('Code Injection')

Opis

The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.

Inne nazwy

Code Injection

Skutki

• Access Control

  Bypass Protection Mechanism

  In some cases, injectable code controls authentication; this may lead to a remote vulnerability.

• Access Control

  Gain Privileges or Assume Identity

  Injected code can access resources that the attacker is directly prevented from accessing.

• Integrity, Confidentiality, Availability

  Execute Unauthorized Code or Commands

  When a product allows a user's input to contain code syntax, it might be possible for an attacker to craft the code in such a way that it will alter the intended control flow of the product. As a result, code injection can often result in the execution of arbitrary code. Code injection attacks can also lead to loss of data integrity in nearly all cases, since the control-plane data injected is always incidental to data recall or writing.

• Non-Repudiation

  Hide Activities

  Often the actions performed by injected control code are unlogged.

Zapobieganie

• Architecture and Design · Refactoring

  Refactor your program so that you do not have to dynamically generate code.

• Architecture and Design

  Run your code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which code can be executed by your product.

  Examples include the Unix chroot jail and AppArmor. In general, managed code may provide some protection.

  This may not be a feasible solution, and it only limits the impact to the operating system; the rest of your application may still be subject to compromise.

  Be careful to avoid CWE-243 and other weaknesses related to jails.

• Implementation · Input Validation

  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.

  To reduce the likelihood of code injection, use stringent allowlists that limit which constructs are allowed. If you are dynamically constructing code that invokes a function, then verifying that the input is alphanumeric might be insufficient. An attacker might still be able to reference a dangerous function that you did not intend to allow, such as system(), exec(), or exit().

• Testing

  Use dynamic tools and techniques that interact with the product using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The product's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

• Operation · Compilation or Build Hardening

  Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).

• Operation · Environment Hardening

  Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).

• Implementation

  For Python programs, it is frequently encouraged to use the ast.literal_eval() function instead of eval, since it is intentionally designed to avoid executing code. However, an adversary could still cause excessive memory or stack consumption via deeply nested structures [REF-1372], so the python documentation discourages use of ast.literal_eval() on untrusted data [REF-1373].

  Skuteczność: Discouraged Common Practice

Przykłady podatności

• CVE-2023-29374 Math component in an LLM framework translates user input into a Python expression that is input into the Python exec() method, allowing code execution - one variant of a "prompt injection" attack.
• CVE-2024-5565 Python-based library uses an LLM prompt containing user input to dynamically generate code that is then fed as input into the Python exec() method, allowing code execution - one variant of a "prompt injection" attack.
• CVE-2024-4181 Framework for LLM applications allows eval injection via a crafted response from a hosting provider.
• CVE-2022-2054 Python compiler uses eval() to execute malicious strings as Python code.
• CVE-2021-22204 Chain: regex in EXIF processor code does not correctly determine where a string ends (CWE-625), enabling eval injection (CWE-95), as exploited in the wild per CISA KEV.
• CVE-2020-8218 "Code injection" in VPN product, as exploited in the wild per CISA KEV.
• 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.
• CVE-2002-0495 Perl code directly injected into CGI library file from parameters to another CGI program.
• CVE-2005-1876 Direct PHP code injection into supporting template file.
• CVE-2005-1894 Direct code injection into PHP script that can be accessed by attacker.
• CVE-2003-0395 PHP code from User-Agent HTTP header directly inserted into log file implemented as PHP script.

Słabość nadrzędna

• CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
• CWE-913 Improper Control of Dynamically-Managed Code Resources

Słabości podrzędne

• CWE-95 Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection')
• CWE-96 Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')
• CWE-1336 Improper Neutralization of Special Elements Used in a Template Engine

Kiedy powstaje

• Implementation — REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Dotyczy

Interpreted, AI/ML

Uwagi

Injection problems encompass a wide variety of issues -- all mitigated in very different ways. For this reason, the most effective way to discuss these weaknesses is to note the distinct features that classify them as injection weaknesses. The most important issue to note is that all injection problems share one thing in common -- i.e., they allow for the injection of control plane data into the user-controlled data plane. This means that the execution of the process may be altered by sending code in through legitimate data channels, using no other mechanism. While buffer overflows, and many other flaws, involve the use of some further issue to gain execution, injection problems need only for the data to be parsed. The most classic instantiations of this category of weakness are SQL injection and format string vulnerabilities.

Źródła

1. 24 Deadly Sins of Software Security — Michael Howard, David LeBlanc, John Viega, "Sin 3: Web-Client Related Vulnerabilities (XSS)." Page 63, McGraw-Hill, 2010
2. How ast.literal_eval can cause memory exhaustion — Reddit, 2022
3. ast - Abstract Syntax Trees — ast.literal_eval(node_or_string), Python, 2023