CWE-138 对特殊元素的转义处理不恰当

Improper Neutralization of Special Elements

结构: Simple

Abstraction: Class

状态: Draft

被利用可能性: unkown

基本描述

The software receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as control elements or syntactic markers when they are sent to a downstream component.

扩展描述

Most languages and protocols have their own special elements such as characters and reserved words. These special elements can carry control implications. If software does not prevent external control or influence over the inclusion of such special elements, the control flow of the program may be altered from what was intended. For example, both Unix and Windows interpret the symbol

相关缺陷

• cwe_Nature: ChildOf cwe_CWE_ID: 707 cwe_View_ID: 1000 cwe_Ordinal: Primary

• cwe_Nature: ChildOf cwe_CWE_ID: 74 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

Implementation

策略:

Developers should anticipate that special elements (e.g. delimiters, symbols) will be injected into input vectors of their software system. One defense is to create a whitelist (e.g. a regular expression) that defines valid input according to the requirements specifications. Strictly filter any input that does not match against the whitelist. Properly encode your output, and quote any elements that have special meaning to the component with which you are communicating.

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.

Implementation

策略:

Use and specify an appropriate output encoding to ensure that the special elements are well-defined. A normal byte sequence in one encoding could be a special element in another.

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.

MIT-28 Implementation

策略: Output Encoding

While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict whitelist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).

分析过的案例

Notes

Relationship
This weakness can be related to interpretation conflicts or interaction errors in intermediaries (such as proxies or application firewalls) when the intermediary's model of an endpoint does not account for protocol-specific special elements.
Relationship
See this entry's children for different types of special elements that have been observed at one point or another. However, it can be difficult to find suitable CVE examples. In an attempt to be complete, CWE includes some types that do not have any associated observed example.
Research Gap
This weakness is probably under-studied for proprietary or custom formats. It is likely that these issues are fairly common in applications that use their own custom format for configuration files, logs, meta-data, messaging, etc. They would only be found by accident or with a focused effort based on an understanding of the format.

分类映射

相关攻击模式

• CAPEC-15

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