CAPEC-178: Cross-Site Flashing

Overview

CAPEC-178 (Cross-Site Flashing) is a detailed-level attack pattern catalogued by MITRE in the Common Attack Pattern Enumeration and Classification (CAPEC). It describes a recurring method attackers use to exploit software weaknesses.

How the attack works

The phases an attacker typically follows to carry out this attack.

Step 1
Explore
[Identification] Using a browser or an automated tool, an attacker records all instances of URLs (or partial URL such as domain) passed to a flash file (SWF).
- Use an automated tool to record the variables passed to a flash file.
- Use a browser to manually explore the website and analyze how the flash file receive variables, e.g. JavaScript using SetVariable/GetVariable, HTML FlashVars param tag, etc.
- Use decompilers to retrieve the flash source code and record all user-controllable variables passed to a loadMovie* directive.
Step 2
Experiment
[Attempt to inject a remote flash file] The attacker makes use of a remotely available flash file (SWF) that generates a uniquely identifiable output when executed inside the targeted flash file.
- Modify the variable of the SWF file that contains the remote movie URL to the attacker controlled flash file.
Step 3
Exploit
[Access or Modify Flash Application Variables] As the attacker succeeds in exploiting the vulnerability, they target the content of the flash application to steal variable content, password, etc.
- Develop malicious Flash application that is injected through vectors identified during the Experiment Phase and loaded by the victim browser's flash plugin and sends document information to the attacker.
- Develop malicious Flash application that is injected through vectors identified during the Experiment Phase and takes commands from an attacker's server and then causes the flash application to execute appropriately.
Step 4
Exploit
[Execute JavaScript in victim's browser] When the attacker targets the current flash application, they can choose to inject JavaScript in the client's DOM and therefore execute cross-site scripting attack.
- Develop malicious JavaScript that is injected from the rogue flash movie to the targeted flash application through vectors identified during the Experiment Phase and loaded by the victim's browser.

What the attacker needs

Prerequisites

The targeted Flash application must reference external URLs and the locations thus referenced must be controllable through parameters. The Flash application must fail to sanitize such parameters against malicious manipulation. The victim must follow a crafted link created by the attacker.

Skills required

Medium skill: knowledge of Flash internals, parameters and remote referencing.

Consequences

What a successful CAPEC-178 attack can achieve.

Modify Data

Affects: Integrity

Read Data

Affects: Confidentiality

Execute Unauthorized Commands

Affects: Authorization

Run Arbitrary Code

Gain Privileges

Affects: Accountability, Authentication, Authorization, Non-Repudiation

Bypass Protection Mechanism

Affects: Access Control, Authorization

How to mitigate it

Defenses that reduce the risk of CAPEC-178.

Implementation: Only allow known URL to be included as remote flash movies in a flash application
Configuration: Properly configure the crossdomain.xml file to only include the known domains that should host remote flash movies.

Examples

The attacker tries to get their malicious flash movie to be executed in the targeted flash application. The malicious file is hosted on the attacker.com domain and the targeted flash application is hosted on example.com The crossdomain.xml file in the root of example.com allows all domains and no specific restriction is specified in the targeted flash application. When the attacker injects their malicious file in the vulnerable flash movie, the rogue flash application is able to access internal variables and parameter of the flash movie.

The CWE weaknesses that CAPEC-178 exploits.

CWE-601: URL Redirection to Untrusted Site ('Open Redirect')

How this attack relates to others in the CAPEC hierarchy.

Parent

CAPEC-182: Flash Injection

Frequently asked questions

Common questions about CAPEC-178.

What is CAPEC-178?

An attacker is able to trick the victim into executing a Flash document that passes commands or calls to a Flash player browser plugin, allowing the attacker to exploit native Flash functionality in the client browser. This attack pattern occurs where an attacker can provide a crafted link to a Flash document (SWF file) which, when followed, will cause additional malicious instructions to be executed. The attacker does not need to serve or control the Flash document. The attack takes advantage of the fact that Flash files can reference external URLs. If variables that serve as URLs that the Flash application references can be controlled through parameters, then by creating a link that includes values for those parameters, an attacker can cause arbitrary content to be referenced and possibly executed by the targeted Flash application.

How does a Cross-Site Flashing attack work?

It typically unfolds over 4 phases. It begins with: [Identification] Using a browser or an automated tool, an attacker records all instances of URLs (or partial URL such as domain) passed to a flash file (SWF).

How do you prevent CAPEC-178?

Implementation: Only allow known URL to be included as remote flash movies in a flash application

What weaknesses does CAPEC-178 target?

CAPEC-178 exploits 1 CWE weakness, including CWE-601 (URL Redirection to Untrusted Site ('Open Redirect')).

How severe is CAPEC-178?

MITRE rates CAPEC-178 as Medium severity with medium likelihood of attack.

References

Attack-pattern data is sourced from the MITRE CAPEC catalog (v3.9). Weakness associations link to the corresponding CWE entries on RadicalNotion.AI.