CWE-138: Improper Neutralization of Special Elements
CWE版本: 4.18
更新日期: 2025-09-09
弱点描述
The product 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 product 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 < ("less than") as meaning "read input from a file".
常见后果
影响范围: Confidentiality Integrity Availability Other
技术影响: Execute Unauthorized Code or Commands Alter Execution Logic DoS: Crash, Exit, or Restart
潜在缓解措施
阶段: Implementation
描述: Developers should anticipate that special elements (e.g. delimiters, symbols) will be injected into input vectors of their product. One defense is to create an allowlist (e.g. a regular expression) that defines valid input according to the requirements specifications. Strictly filter any input that does not match against the allowlist. Properly encode your output, and quote any elements that have special meaning to the component with which you are communicating.
阶段: Implementation
策略: Input Validation
阶段: Implementation
描述: 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.
阶段: Implementation
策略: Input Validation
描述: 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 allowlist validation schemes by introducing dangerous inputs after they have been checked.
阶段: Implementation
策略: Output Encoding
描述: 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 allowlist (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).
观察示例
参考: CVE-2001-0677
Read arbitrary files from mail client by providing a special MIME header that is internally used to store pathnames for attachments.
参考: CVE-2000-0703
Setuid program does not cleanse special escape sequence before sending data to a mail program, causing the mail program to process those sequences.
参考: CVE-2003-0020
Multi-channel issue. Terminal escape sequences not filtered from log files.
参考: CVE-2003-0083
Multi-channel issue. Terminal escape sequences not filtered from log files.
引入模式
| 阶段 | 说明 |
|---|---|
| Implementation | REALIZATION: This weakness is caused during implementation of an architectural security tactic. |
适用平台
编程语言
分类映射
| 分类名称 | 条目ID | 条目名称 | 映射适配度 |
|---|---|---|---|
| PLOVER | - | Special Elements (Characters or Reserved Words) | - |
| PLOVER | - | Custom Special Character Injection | - |
| Software Fault Patterns | SFP24 | Tainted input to command | - |