CWE-472 对假设不可变Web参数的外部可控制

External Control of Assumed-Immutable Web Parameter

结构: Simple

Abstraction: Base

状态: Draft

被利用可能性: unkown

基本描述

The web application does not sufficiently verify inputs that are assumed to be immutable but are actually externally controllable, such as hidden form fields.

扩展描述

If a web product does not properly protect assumed-immutable values from modification in hidden form fields, parameters, cookies, or URLs, this can lead to modification of critical data. Web applications often mistakenly make the assumption that data passed to the client in hidden fields or cookies is not susceptible to tampering. Improper validation of data that are user-controllable can lead to the application processing incorrect, and often malicious, input.

For example, custom cookies commonly store session data or persistent data across sessions. This kind of session data is normally involved in security related decisions on the server side, such as user authentication and access control. Thus, the cookies might contain sensitive data such as user credentials and privileges. This is a dangerous practice, as it can often lead to improper reliance on the value of the client-provided cookie by the server side application.

相关缺陷

• cwe_Nature: ChildOf cwe_CWE_ID: 642 cwe_View_ID: 1000 cwe_Ordinal: Primary

• cwe_Nature: ChildOf cwe_CWE_ID: 471 cwe_View_ID: 1000

• cwe_Nature: ChildOf cwe_CWE_ID: 471 cwe_View_ID: 699 cwe_Ordinal: Primary

适用平台

Language: {'cwe_Class': 'Language-Independent', 'cwe_Prevalence': 'Undetermined'}

常见的影响

可能的缓解方案

MIT-5 Implementation

策略: 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.

MIT-20 Implementation

策略: Input Validation

Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass whitelist validation schemes by introducing dangerous inputs after they have been checked.

示例代码

例

In this example, a web application uses the value of a hidden form field (accountID) without having done any input validation because it was assumed to be immutable.

bad Java

例

Hidden fields should not be trusted as secure parameters.

An attacker can intercept and alter hidden fields in a post to the server as easily as user input fields. An attacker can simply parse the HTML for the substring:

bad HTML

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