CWE-116

出力の不適切なエンコードまたはエスケープ

Improper Encoding or Escaping of Output

脆弱性レビュー中

日本語説明

製品が他のコンポーネントと通信するために構造化されたメッセージを準備するが、データのエンコードまたはエスケープが欠落しているか、正しく行われていない。その結果、意図したメッセージの構造が保持されない。

不適切なエンコードやエスケープにより、攻撃者は別のコンポーネントに送信されるコマンドを変更し、代わりに悪意のあるコマンドを挿入することができる。

ほとんどの製品は、クエリーやコマンドなど、コンポーネント間の通信に構造化メッセージを使用する特定のプロトコルに従います。これらの構造化メッセージには、メタデータや制御情報が散りばめられた生データが含まれることがある。例えば、"GET /index.html HTTP/1.1 "は、単一の引数("/index.html")を持つコマンド("GET")と、どのプロトコルのバージョンが使われているかについてのメタデータ("HTTP/1.1")を含む構造化メッセージです。

もしアプリケーションが攻撃者から提供された入力を使って、適切にエンコードやエスケープを行わずに構造化メッセージを構築すると、攻撃者はデータを制御情報やメタデータとして解釈させる特殊文字を挿入する可能性があります。その結果、出力を受信したコンポーネントは間違った操作を実行したり、データを正しく解釈できなくなります。

原文 (English)

The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

Improper encoding or escaping can allow attackers to change the commands that are sent to another component, inserting malicious commands instead.

Most products follow a certain protocol that uses structured messages for communication between components, such as queries or commands. These structured messages can contain raw data interspersed with metadata or control information. For example, "GET /index.html HTTP/1.1" is a structured message containing a command ("GET") with a single argument ("/index.html") and metadata about which protocol version is being used ("HTTP/1.1").

If an application uses attacker-supplied inputs to construct a structured message without properly encoding or escaping, then the attacker could insert special characters that will cause the data to be interpreted as control information or metadata. Consequently, the component that receives the output will perform the wrong operations, or otherwise interpret the data incorrectly.

関連する脆弱性

想定される影響

Scope: Integrity / Impact: Modify Application Data

Scope: Integrity, Confidentiality, Availability, Access Control / Impact: Execute Unauthorized Code or Commands

Scope: Confidentiality / Impact: Bypass Protection Mechanism

対策・緩和策

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

For example, consider using the ESAPI Encoding control [REF-45] or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error.

Alternately, use built-in functions, but consider using wrappers in case those functions are discovered to have a vulnerability.

If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.

For example, stored procedures can enforce database query structure and reduce the likelihood of SQL injection.

Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies.

In some cases, input validation may be an important strategy when output encoding is not a complete solution. For example, you may be providing the same output that will be processed by multiple consumers that use different encodings or representations. In other cases, you may be required to allow user-supplied input to contain control information, such as limited HTML tags that support formatting in a wiki or bulletin board. When this type of requirement must be met, use an extremely strict allowlist to limit which control sequences can be used. Verify that the resulting syntactic structure is what you expect. Use your normal encoding methods for the remainder of the input.

Use input validation as a defense-in-depth measure to reduce the likelihood of output encoding errors (see CWE-20).

Fully specify which encodings are required by components that will be communicating with each other.

When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.

外部リンク

MITRE公式ページ — CWE-116