 Description An adversary utilizes a form of Cross-site Scripting (XSS) where a malicious script is persistently "stored" within the data storage of a vulnerable web application as valid input. Extended Description Initially presented by an adversary to the vulnerable web application, the malicious script is incorrectly considered valid input and is not properly encoded by the web application. A victim is then convinced to use the web application in a way that creates a response that includes the malicious script. This response is subsequently sent to the victim and the malicious script is executed by the victim's browser. To launch a successful Stored XSS attack, an adversary looks for places where stored input data is used in the generation of a response. This often involves elements that are not expected to host scripts such as image tags (<img>), or the addition of event attributes such as onload and onmouseover. These elements are often not subject to the same input validation, output encoding, and other content filtering and checking routines. Likelihood Of Attack Typical Severity Relationships  This table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.| Nature | Type | ID | Name |
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| ChildOf |  Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern. | 63 | Cross-Site Scripting (XSS) | | ParentOf |  Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 18 | XSS Targeting Non-Script Elements | | ParentOf | Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 32 | XSS Through HTTP Query Strings | | ParentOf | Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 86 | XSS Through HTTP Headers | | ParentOf | Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 198 | XSS Targeting Error Pages | | ParentOf | Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 199 | XSS Using Alternate Syntax | | ParentOf | Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 209 | XSS Using MIME Type Mismatch | | ParentOf | Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 243 | XSS Targeting HTML Attributes | | ParentOf | Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 244 | XSS Targeting URI Placeholders | | ParentOf | Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 245 | XSS Using Doubled Characters | | ParentOf | Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 247 | XSS Using Invalid Characters | | CanFollow | Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern. | 73 | User-Controlled Filename | | CanFollow | Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal. | 93 | Log Injection-Tampering-Forging |
Execution Flow Explore Survey the application for stored user-controllable inputs: Using a browser or an automated tool, an adversary follows all public links and actions on a web site. They record all the links, the forms, the resources accessed and all other potential entry-points for the web application. The adversary is looking for areas where user input is stored, such as user profiles, shopping carts, file managers, forums, blogs, and logs. | Techniques |
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| Use a spidering tool to follow and record all links and analyze the web pages to find entry points. | | Use a proxy tool to record all links visited during a manual traversal of the web application. | | Use a browser to manually explore the website and analyze how it is constructed. Many browsers' plugins are available to facilitate the analysis or automate the discovery. |
Experiment Probe identified potential entry points for stored XSS vulnerability: The adversary uses the entry points gathered in the "Explore" phase as a target list and injects various common script payloads and special characters to determine if an entry point actually represents a vulnerability and to characterize the extent to which the vulnerability can be exploited. | Techniques |
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| Use a list of XSS probe strings to submit script in input fields that could be stored by the web application. If possible, the probe strings contain a unique identifier so they can be queried for after submitting to see if they are stored. | | Use a list of HTML special characters to submit in input fields that could be stored by the web application and check if they were properly encoded, replaced, or filtered out. |
Store malicious XSS content: Once the adversary has determined which stored locations are vulnerable to XSS, they will interact with the web application to store the malicious content. The adversary can have many goals, from stealing session IDs, cookies, credentials, and page content from a victim. | Techniques |
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| Store a malicious script on a page that will execute when viewed by the victim. | | Use a tool such as BeEF to store a hook into the web application. This will alert the adversary when the victim has accessed the content and will give the adversary control over the victim's browser, allowing them access to cookies, user screenshot, user clipboard, and more complex XSS attacks. |
Exploit Get victim to view stored content: In order for the attack to be successful, the victim needs to view the stored malicious content on the webpage. | Techniques |
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| Send a phishing email to the victim containing a URL that will direct them to the malicious stored content. | | Simply wait for a victim to view the content. This is viable in situations where content is posted to a popular public forum. |
Prerequisites
| An application that leverages a client-side web browser with scripting enabled. |
| An application that fails to adequately sanitize or encode untrusted input. |
| An application that stores information provided by the user in data storage of some kind. |
Skills Required
[Level: Medium] Requires the ability to write scripts of varying complexity and to inject them through user controlled fields within the application. |
Resources Required
| None: No specialized resources are required to execute this type of attack. |
Consequences This table specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.| Scope | Impact | Likelihood |
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Confidentiality | Read Data | | Confidentiality Authorization Access Control | Gain Privileges | | Confidentiality Integrity Availability | Execute Unauthorized Commands | | Integrity | Modify Data | |
Mitigations
| Use browser technologies that do not allow client-side scripting. |
| Utilize strict type, character, and encoding enforcement. |
| Ensure that all user-supplied input is validated before being stored. |
Example Instances
| An adversary determines that a system uses a web based interface for administration. The adversary creates a new user record and supplies a malicious script in the user name field. The user name field is not validated by the system and a new log entry is created detailing the creation of the new user. Later, an administrator reviews the log in the administrative console. When the administrator comes across the new user entry, the browser sees a script and executes it, stealing the administrator's authentication cookie and forwarding it to the adversary. An adversary then uses the received authentication cookie to log in to the system as an administrator, provided that the administrator console can be accessed remotely. |
| An online discussion forum allows its members to post HTML-enabled messages, which can also include image tags. An adversary embeds JavaScript in the image tags of their message. The adversary then sends the victim an email advertising free goods and provides a link to the form for how to collect. When the victim visits the forum and reads the message, the malicious script is executed within the victim's browser. |
References  Content History | Submissions |
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| Submission Date | Submitter | Organization |
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| 2017-04-15 (Version 2.9) | CAPEC Content Team | The MITRE Corporation | | | Modifications |
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| Modification Date | Modifier | Organization |
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| 2017-08-04 (Version 2.11) | CAPEC Content Team | The MITRE Corporation | | Updated Resources_Required | | 2019-04-04 (Version 3.1) | CAPEC Content Team | The MITRE Corporation | | Updated Related_Weaknesses | | 2019-09-30 (Version 3.2) | CAPEC Content Team | The MITRE Corporation | | Updated Description | | 2020-07-30 (Version 3.3) | CAPEC Content Team | The MITRE Corporation | | Updated Example_Instances | | 2020-12-17 (Version 3.4) | CAPEC Content Team | The MITRE Corporation | | Updated References | | 2022-02-22 (Version 3.7) | CAPEC Content Team | The MITRE Corporation | | Updated Execution_Flow | | 2022-09-29 (Version 3.8) | CAPEC Content Team | The MITRE Corporation | | Updated Description, Extended_Description |
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