CAPEC-698
Install Malicious Extension
An adversary directly installs or tricks a user into installing a malicious extension into existing trusted software, with the goal of achieving a variety of negative technical impacts.
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Many software applications allow users to install third-party software extensions/plugins that provide additional features and functionality. Adversaries can take advantage of this behavior to install malware on a system with relative ease. This may require the adversary compromising a system and then installing the malicious extension themself. An alternate approach entails masquerading the malicious extension as a legitimate extension. The adversary then convinces users to install the malicious component, via means such as social engineering, or simply waits for victims to unknowingly install the malware on their systems. Once the malicious extension has been installed, the adversary can achieve a variety of negative technical impacts such as obtaining sensitive information, executing unauthorized commands, observing/modifying network traffic, and more.
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Explain the attack pattern CAPEC-698: Install Malicious Extension: how it unfolds, what it needs and how to prevent and detect it in my systems. Use https://capec.mitre.org/data/definitions/698.html and https://cve.bz/cve/capec/698?via=ask-ai-copy, which lists recent CVEs with the weaknesses it exploits. Cite the sources.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this attack pattern's id and public links.
How the attack unfolds
Explore
The attacker looks for a way in.
[Identify target(s)] The adversary must first identify target software that allows for extensions/plugins and which they wish to exploit, such as a web browser or desktop application. To increase the attack space, this will often be popular software with a large user-base.
Experiment
They probe what they found.
[Create malicious extension] Having identified a suitable target, the adversary crafts a malicious extension/plugin that can be installed by the underlying target software. This malware may be targeted to execute on specific operating systems or be operating system agnostic.
Exploit
They carry out the attack.
[Install malicious extension] The malicious extension/plugin is installed by the underlying target software and executes the adversary-created malware, resulting in a variety of negative technical impacts.
2 techniques
- Adversary-Installed: Having already compromised the target system, the adversary simply installs the malicious extension/plugin themself.
- User-Installed: The adversary tricks the user into installing the malicious extension/plugin, via means such as social engineering, or may upload the malware on a reputable extension/plugin hosting site and wait for unknowing victims to install the malicious component.
Prerequisites
The adversary must craft malware based on the type of software and system(s) they intend to exploit.
If the adversary intends to install the malicious extension themself, they must first compromise the target machine via some other means.
Skills required
- Medium skill
Ability to create malicious extensions that can exploit specific software applications and systems.
- Medium skill
Optional: Ability to exploit target system(s) via other means in order to gain entry.
Consequences
| Impact | Affects | Note |
|---|---|---|
| Read Data | Confidentiality, Access Control | |
| Modify Data | Integrity, Access Control | |
| Execute Unauthorized Commands, Alter Execution Logic, Gain Privileges | Authorization, Access Control |
Mitigations
Only install extensions/plugins from official/verifiable sources.
Confirm extensions/plugins are legitimate and not malware masquerading as a legitimate extension/plugin.
Ensure the underlying software leveraging the extension/plugin (including operating systems) is up-to-date.
Implement an extension/plugin allow list, based on the given security policy.
If applicable, confirm extensions/plugins are properly signed by the official developers.
For web browsers, close sessions when finished to prevent malicious extensions/plugins from executing the the background.
Weaknesses it exploits
Recent CVEs with these weaknesses
- 4.4CVE-2026-123858
In JetBrains PhpStorm before 2026.3 project files could be automatically uploaded to a deployment server from untrusted projects
- 5.5CVE-2026-123854
In JetBrains PyCharm before 2026.3 code execution was possible in Safe Mode via a crafted Jupyter notebook widget module
- 7.8CVE-2026-123853
In JetBrains IntelliJ IDEA before 2026.3, 2026.2.2 code execution was possible in Safe Mode via project-controlled JVM options of the build process
- 7.0CVE-2026-123849
In JetBrains IntelliJ IDEA before 2026.3 code execution was possible in untrusted projects via the Terraform File Watchers
- 3.3CVE-2026-123843
In JetBrains IntelliJ IDEA before 2026.3 untrusted projects could trigger changes to GPG agent configuration
- 7.8CVE-2026-123838
In JetBrains IntelliJ IDEA before 2026.3 code execution was possible in Safe Mode via UI Designer form file
- 3.6CVE-2026-123833
In JetBrains IntelliJ IDEA before 2026.3 database connections could be established in untrusted projects
- 9.6CVE-2026-123832
In JetBrains CLion before 2026.2 code execution was possible in Safe Mode via JSON compilation database
The newest records naming one of them. Each weakness's page lists them all.
Related attack patterns
- Part of
- CAPEC-542 Targeted Malware
Examples
In January 2018, Palo Alto's Unit 42 reported that a malicious Internet Information Services (IIS) extension …
In January 2018, Palo Alto's Unit 42 reported that a malicious Internet Information Services (IIS) extension they named RGDoor was used to create a backdoor into several Middle Eastern government organizations, as well as a financial institution and an educational institution. This malware was used in conjunction with the TwoFace webshell and allowed the adversaries to upload/download files and execute unauthorized commands. [REF-740]
In December 2018, it was reported that North Korea-based APT Kimusky (also known as Velvet Chollima) infected…
In December 2018, it was reported that North Korea-based APT Kimusky (also known as Velvet Chollima) infected numerous legitimate academic organizations within the U.S., many specializing in biomedical engineering, with a malicious Google Chrome extension. Dubbed "Operation STOLEN PENCIL", the attack entailed conducting spear-phishing attacks to trick victims into installing a malicious PDF reader named "Auto Font Manager". Once installed, the malware allowed adversaries to steal cookies and site passwords, as well as forward emails from some compromised accounts. [REF-741]
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