CWE-243 未改变工作目录时创建chroot Jail

Creation of chroot Jail Without Changing Working Directory

结构: Simple

Abstraction: Variant

状态: Draft

被利用可能性: High

基本描述

The program uses the chroot() system call to create a jail, but does not change the working directory afterward. This does not prevent access to files outside of the jail.

扩展描述

Improper use of chroot() may allow attackers to escape from the chroot jail. The chroot() function call does not change the process's current working directory, so relative paths may still refer to file system resources outside of the chroot jail after chroot() has been called.

适用平台

Language: [{'cwe_Name': 'C', 'cwe_Prevalence': 'Undetermined'}, {'cwe_Name': 'C++', 'cwe_Prevalence': 'Undetermined'}]

Operating_System: {'cwe_Class': 'Unix', 'cwe_Prevalence': 'Undetermined'}

常见的影响

范围	影响	注释
Confidentiality	Read Files or Directories

示例代码

例

Consider the following source code from a (hypothetical) FTP server:

bad C

chroot("/var/ftproot");
...
fgets(filename, sizeof(filename), network);
localfile = fopen(filename, "r");
while ((len = fread(buf, 1, sizeof(buf), localfile)) != EOF) {

fwrite(buf, 1, sizeof(buf), network);

}
fclose(localfile);

This code is responsible for reading a filename from the network, opening the corresponding file on the local machine, and sending the contents over the network. This code could be used to implement the FTP GET command. The FTP server calls chroot() in its initialization routines in an attempt to prevent access to files outside of /var/ftproot. But because the server does not change the current working directory by calling chdir("/"), an attacker could request the file "../../../../../etc/passwd" and obtain a copy of the system password file.

分类映射

映射的分类名	ImNode ID	Fit	Mapped Node Name
7 Pernicious Kingdoms			Directory Restriction
Software Fault Patterns	SFP17		Failed chroot jail

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