Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection')

Opis

The product 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").

Skutki

• Confidentiality

  Read Files or Directories; Read Application 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 or Assume Identity

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

• Integrity, Confidentiality, Availability, Other

  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 or at least modify what code can be executed.

• Non-Repudiation

  Hide Activities

  Often the actions performed by injected control code are unlogged.

Zapobieganie

• Architecture and Design, Implementation · Refactoring

  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 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.

• 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 allowlist 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.

• 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-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-2021-22205 Chain: backslash followed by a newline can bypass a validation step (CWE-20), leading to eval injection (CWE-95), 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-2007-2713 Chain: Execution after redirect triggers eval injection.

Słabość nadrzędna

• CWE-94 Improper Control of Generation of Code ('Code Injection')

Kiedy powstaje

• Implementation — REALIZATION: This weakness is caused during implementation of an architectural security tactic.
• Implementation — This weakness is prevalent in handler/dispatch procedures that might want to invoke a large number of functions, or set a large number of variables.

Dotyczy

Java, JavaScript, Python, Perl, PHP, Ruby, Interpreted, AI/ML

Uwagi

Factors: special character errors can play a role in increasing the variety of code that can be injected, although some vulnerabilities do not require special characters at all, e.g. when a single function without arguments can be referenced and a terminator character is not necessary.

Źródła

1. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 18, "Inline Evaluation", Page 1095, Addison Wesley, 2006
2. How ast.literal_eval can cause memory exhaustion — Reddit, 2022
3. ast - Abstract Syntax Trees — ast.literal_eval(node_or_string), Python, 2023