COMMON ATTACK PATTERN ENUMERATION AND CLASSIFICATIONLive MITRE record

CAPEC-17

Using Malicious Files

An attack of this type exploits a system's configuration that allows an adversary to either directly access an executable file, for example through shell access; or in a possible worst case allows an adversary to upload a file and then execute it. Web servers, ftp servers, and message oriented middleware systems which have many integration points are particularly vulnerable, because both the programmers and the administrators must be in synch regarding the interfaces and the correct privileges for each interface.

Abstraction

Standard

Typical severity

Very High

Likelihood of attack

High

Understand the attack

What is this attack pattern?

Execution flow

How does the attack proceed, step by step?

Explore

Determine File/Directory Configuration

The adversary looks for misconfigured files or directories on a system that might give executable access to an overly broad group of users.

Techniques used

Through shell access to a system, use the command "ls -l" to view permissions for files and directories.

Experiment

Upload Malicious Files

If the adversary discovers a directory that has executable permissions, they will attempt to upload a malicious file to execute.

Techniques used

Upload a malicious file through a misconfigured FTP server.

Exploit

Execute Malicious File

The adversary either executes the uploaded malicious file, or executes an existing file that has been misconfigured to allow executable access to the adversary.

Requirements

What does the attack require?

Prerequisites

System's configuration must allow an attacker to directly access executable files or upload files to execute. This means that any access control system that is supposed to mediate communications between the subject and the object is set incorrectly or assumes a benign environment.

Skills required

Low: To identify and execute against an over-privileged system interface

Resources required

Ability to communicate synchronously or asynchronously with server that publishes an over-privileged directory, program, or interface. Optionally, ability to capture output directly through synchronous communication or other method such as FTP.

Impact

What does a successful attack lead to?

Execute Unauthorized Commands

Affected scopes: Confidentiality, Integrity, Availability

Modify Data

Affected scopes: Integrity

Read Data

Affected scopes: Confidentiality

Gain Privileges

Affected scopes: Confidentiality, Access Control, Authorization

Defence

How is it prevented and mitigated?

Design: Enforce principle of least privilege

Design: Run server interfaces with a non-root account and/or utilize chroot jails or other configuration techniques to constrain privileges even if attacker gains some limited access to commands.

Implementation: Perform testing such as pen-testing and vulnerability scanning to identify directories, programs, and interfaces that grant direct access to executables.

Real world

MITRE example instances

Example instance 1Detail

Consider a directory on a web server with the following permissions drwxrwxrwx 5 admin public 170 Nov 17 01:08 webroot This could allow an attacker to both execute and upload and execute programs' on the web server. This one vulnerability can be exploited by a threat to probe the system and identify additional vulnerabilities to exploit.