CWE-378 创建拥有不安全权限的临时文件

Creation of Temporary File With Insecure Permissions

结构: Simple

Abstraction: Base

状态: Draft

被利用可能性: High

基本描述

Opening temporary files without appropriate measures or controls can leave the file, its contents and any function that it impacts vulnerable to attack.

相关缺陷

  • cwe_Nature: ChildOf cwe_CWE_ID: 377 cwe_View_ID: 1000 cwe_Ordinal: Primary

适用平台

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

常见的影响

范围 影响 注释
Confidentiality Read Application Data If the temporary file can be read by the attacker, sensitive information may be in that file which could be revealed.
['Authorization', 'Other'] Other If that file can be written to by the attacker, the file might be moved into a place to which the attacker does not have access. This will allow the attacker to gain selective resource access-control privileges.
['Integrity', 'Other'] Other Depending on the data stored in the temporary file, there is the potential for an attacker to gain an additional input vector which is trusted as non-malicious. It may be possible to make arbitrary changes to data structures, user information, or even process ownership.

可能的缓解方案

Requirements

策略:

Many contemporary languages have functions which properly handle this condition. Older C temp file functions are especially susceptible.

Implementation

策略:

Ensure that you use proper file permissions. This can be achieved by using a safe temp file function. Temporary files should be writable and readable only by the process that owns the file.

Implementation

策略:

Randomize temporary file names. This can also be achieved by using a safe temp-file function. This will ensure that temporary files will not be created in predictable places.

示例代码

例

In the following code examples a temporary file is created and written to and after using the temporary file the file is closed and deleted from the file system.

bad C

FILE *stream;
if( (stream = tmpfile()) == NULL ) {

perror("Could not open new temporary file\n");
return (-1);
}
// write data to tmp file
...
// remove tmp file
rmtmp();

However, within this C/C++ code the method tmpfile() is used to create and open the temp file. The tmpfile() method works the same way as the fopen() method would with read/write permission, allowing attackers to read potentially sensitive information contained in the temp file or modify the contents of the file.

bad Java

try {
File temp = File.createTempFile("pattern", ".suffix");
temp.deleteOnExit();
BufferedWriter out = new BufferedWriter(new FileWriter(temp));
out.write("aString");
out.close();
}
catch (IOException e) {
}

Similarly, the createTempFile() method used in the Java code creates a temp file that may be readable and writable to all users.

Additionally both methods used above place the file into a default directory. On UNIX systems the default directory is usually "/tmp" or "/var/tmp" and on Windows systems the default directory is usually "C:\Windows\Temp", which may be easily accessible to attackers, possibly enabling them to read and modify the contents of the temp file.

分类映射

映射的分类名 ImNode ID Fit Mapped Node Name
CLASP Improper temp file opening