CWE-250 带着不必要的权限执行

admin 2022年1月5日21:04:40CWE(弱点枚举)评论9 views12276字阅读40分55秒阅读模式

CWE-250 带着不必要的权限执行

Execution with Unnecessary Privileges

结构: Simple

Abstraction: Class

状态: Draft

被利用可能性: Medium

基本描述

The software performs an operation at a privilege level that is higher than the minimum level required, which creates new weaknesses or amplifies the consequences of other weaknesses.

扩展描述

New weaknesses can be exposed because running with extra privileges, such as root or Administrator, can disable the normal security checks being performed by the operating system or surrounding environment. Other pre-existing weaknesses can turn into security vulnerabilities if they occur while operating at raised privileges.

Privilege management functions can behave in some less-than-obvious ways, and they have different quirks on different platforms. These inconsistencies are particularly pronounced if you are transitioning from one non-root user to another. Signal handlers and spawned processes run at the privilege of the owning process, so if a process is running as root when a signal fires or a sub-process is executed, the signal handler or sub-process will operate with root privileges.

相关缺陷

  • cwe_Nature: ChildOf cwe_CWE_ID: 657 cwe_View_ID: 1000 cwe_Ordinal: Primary

  • cwe_Nature: ChildOf cwe_CWE_ID: 657 cwe_View_ID: 699

  • cwe_Nature: ChildOf cwe_CWE_ID: 269 cwe_View_ID: 1000

适用平台

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

Paradigm: {'cwe_Name': 'Mobile', 'cwe_Prevalence': 'Undetermined'}

常见的影响

范围 影响 注释
['Confidentiality', 'Integrity', 'Availability', 'Access Control'] ['Gain Privileges or Assume Identity', 'Execute Unauthorized Code or Commands', 'Read Application Data', 'DoS: Crash, Exit, or Restart'] An attacker will be able to gain access to any resources that are allowed by the extra privileges. Common results include executing code, disabling services, and reading restricted data.

检测方法

Manual Analysis

This weakness can be detected using tools and techniques that require manual (human) analysis, such as penetration testing, threat modeling, and interactive tools that allow the tester to record and modify an active session.

These may be more effective than strictly automated techniques. This is especially the case with weaknesses that are related to design and business rules.

DM-11.7 Black Box

Use monitoring tools that examine the software's process as it interacts with the operating system and the network. This technique is useful in cases when source code is unavailable, if the software was not developed by you, or if you want to verify that the build phase did not introduce any new weaknesses. Examples include debuggers that directly attach to the running process; system-call tracing utilities such as truss (Solaris) and strace (Linux); system activity monitors such as FileMon, RegMon, Process Monitor, and other Sysinternals utilities (Windows); and sniffers and protocol analyzers that monitor network traffic.

Attach the monitor to the process and perform a login. Look for library functions and system calls that indicate when privileges are being raised or dropped. Look for accesses of resources that are restricted to normal users.

Note that this technique is only useful for privilege issues related to system resources. It is not likely to detect application-level business rules that are related to privileges, such as if a blog system allows a user to delete a blog entry without first checking that the user has administrator privileges.

Automated Static Analysis - Binary or Bytecode

According to SOAR, the following detection techniques may be useful:

Highly cost effective:
  • Compare binary / bytecode to application permission manifest
Cost effective for partial coverage:
  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis
  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Manual Static Analysis - Binary or Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:
  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Dynamic Analysis with Automated Results Interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:
  • Host-based Vulnerability Scanners – Examine configuration for flaws, verifying that audit mechanisms work, ensure host configuration meets certain predefined criteria

Dynamic Analysis with Manual Results Interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:
  • Host Application Interface Scanner

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:
  • Manual Source Code Review (not inspections)
Cost effective for partial coverage:
  • Focused Manual Spotcheck - Focused manual analysis of source

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:
  • Source code Weakness Analyzer
  • Context-configured Source Code Weakness Analyzer

Automated Static Analysis

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:
  • Configuration Checker
  • Permission Manifest Analysis

Architecture or Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:
  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)
  • Formal Methods / Correct-By-Construction
Cost effective for partial coverage:
  • Attack Modeling

可能的缓解方案

MIT-17 ['Architecture and Design', 'Operation']

策略: Environment Hardening

Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.

MIT-18 Architecture and Design

策略: Separation of Privilege

Identify the functionality that requires additional privileges, such as access to privileged operating system resources. Wrap and centralize this functionality if possible, and isolate the privileged code as much as possible from other code [REF-76]. Raise privileges as late as possible, and drop them as soon as possible to avoid CWE-271. Avoid weaknesses such as CWE-288 and CWE-420 by protecting all possible communication channels that could interact with the privileged code, such as a secondary socket that is only intended to be accessed by administrators.

MIT-18 Architecture and Design

策略: Attack Surface Reduction

Identify the functionality that requires additional privileges, such as access to privileged operating system resources. Wrap and centralize this functionality if possible, and isolate the privileged code as much as possible from other code [REF-76]. Raise privileges as late as possible, and drop them as soon as possible to avoid CWE-271. Avoid weaknesses such as CWE-288 and CWE-420 by protecting all possible communication channels that could interact with the privileged code, such as a secondary socket that is only intended to be accessed by administrators.

Implementation

策略:

Perform extensive input validation for any privileged code that must be exposed to the user and reject anything that does not fit your strict requirements.

MIT-19 Implementation

策略:

When dropping privileges, ensure that they have been dropped successfully to avoid CWE-273. As protection mechanisms in the environment get stronger, privilege-dropping calls may fail even if it seems like they would always succeed.

Implementation

策略:

If circumstances force you to run with extra privileges, then determine the minimum access level necessary. First identify the different permissions that the software and its users will need to perform their actions, such as file read and write permissions, network socket permissions, and so forth. Then explicitly allow those actions while denying all else [REF-76]. Perform extensive input validation and canonicalization to minimize the chances of introducing a separate vulnerability. This mitigation is much more prone to error than dropping the privileges in the first place.

MIT-37 ['Operation', 'System Configuration']

策略: Environment Hardening

Ensure that the software runs properly under the Federal Desktop Core Configuration (FDCC) [REF-199] or an equivalent hardening configuration guide, which many organizations use to limit the attack surface and potential risk of deployed software.

示例代码

This code temporarily raises the program's privileges to allow creation of a new user folder.

bad Python

def makeNewUserDir(username):

if invalidUsername(username):


#avoid CWE-22 and CWE-78

print('Usernames cannot contain invalid characters')
return False

try:

raisePrivileges()
os.mkdir('/home/' + username)
lowerPrivileges()

except OSError:

print('Unable to create new user directory for user:' + username)
return False

return True

While the program only raises its privilege level to create the folder and immediately lowers it again, if the call to os.mkdir() throws an exception, the call to lowerPrivileges() will not occur. As a result, the program is indefinitely operating in a raised privilege state, possibly allowing further exploitation to occur.

The following code calls chroot() to restrict the application to a subset of the filesystem below APP_HOME in order to prevent an attacker from using the program to gain unauthorized access to files located elsewhere. The code then opens a file specified by the user and processes the contents of the file.

bad C

chroot(APP_HOME);
chdir("/");
FILE* data = fopen(argv[1], "r+");
...

Constraining the process inside the application's home directory before opening any files is a valuable security measure. However, the absence of a call to setuid() with some non-zero value means the application is continuing to operate with unnecessary root privileges. Any successful exploit carried out by an attacker against the application can now result in a privilege escalation attack because any malicious operations will be performed with the privileges of the superuser. If the application drops to the privilege level of a non-root user, the potential for damage is substantially reduced.

This application intends to use a user's location to determine the timezone the user is in:

bad Java

locationClient = new LocationClient(this, this, this);
locationClient.connect();
Location userCurrLocation;
userCurrLocation = locationClient.getLastLocation();
setTimeZone(userCurrLocation);

This is unnecessary use of the location API, as this information is already available using the Android Time API. Always be sure there is not another way to obtain needed information before resorting to using the location API.

This code uses location to determine the user's current US State location.

First the application must declare that it requires the ACCESS_FINE_LOCATION permission in the application's manifest.xml:

bad XML

During execution, a call to getLastLocation() will return a location based on the application's location permissions. In this case the application has permission for the most accurate location possible:

bad Java

locationClient = new LocationClient(this, this, this);
locationClient.connect();
Location userCurrLocation;
userCurrLocation = locationClient.getLastLocation();
deriveStateFromCoords(userCurrLocation);

While the application needs this information, it does not need to use the ACCESS_FINE_LOCATION permission, as the ACCESS_COARSE_LOCATION permission will be sufficient to identify which US state the user is in.

分析过的案例

标识 说明 链接
CVE-2007-4217 FTP client program on a certain OS runs with setuid privileges and has a buffer overflow. Most clients do not need extra privileges, so an overflow is not a vulnerability for those clients. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-4217
CVE-2008-1877 Program runs with privileges and calls another program with the same privileges, which allows read of arbitrary files. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-1877
CVE-2007-5159 OS incorrectly installs a program with setuid privileges, allowing users to gain privileges. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-5159
CVE-2008-4638 Composite: application running with high privileges allows user to specify a restricted file to process, which generates a parsing error that leaks the contents of the file. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-4638
CVE-2008-0162 Program does not drop privileges before calling another program, allowing code execution. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-0162
CVE-2008-0368 setuid root program allows creation of arbitrary files through command line argument. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-0368
CVE-2007-3931 Installation script installs some programs as setuid when they shouldn't be. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-3931

Notes

Relationship
There is a close association with CWE-653 (Insufficient Separation of Privileges). CWE-653 is about providing separate components for each privilege; CWE-250 is about ensuring that each component has the least amount of privileges possible.
Maintenance
CWE-271, CWE-272, and CWE-250 are all closely related and possibly overlapping. CWE-271 is probably better suited as a category. Both CWE-272 and CWE-250 are in active use by the community. The "least privilege" phrase has multiple interpretations.

分类映射

映射的分类名 ImNode ID Fit Mapped Node Name
7 Pernicious Kingdoms Often Misused: Privilege Management
The CERT Oracle Secure Coding Standard for Java (2011) SER09-J Minimize privileges before deserializing from a privilege context

相关攻击模式

  • CAPEC-104
  • CAPEC-470
  • CAPEC-69

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