Dissecting the "7Bnew20javaxscriptScriptEngineManager2829..." String: A Security Deep-Dive into Obfuscated Payloads and Confluence Exploits

The string 7Bnew20javaxscriptScriptEngineManager2829getEngineByName2827nashorn2729eval2827cat20confluencecfgxml27297D is not a benign software artifact; it is a characteristic signature of an obfuscated JavaScript payload targeting Apache Confluence servers. This article provides an analytical breakdown of the string’s composition, the underlying JavaScript engine abuse, and the specific vulnerability class it exploits. For security professionals, developers, and IT administrators, understanding this pattern is critical for identifying active intrusions and assessing risk exposure.

Key Takeaways

• Payload Identification: The string represents a hex-encoded and compressed JavaScript command chain that invokes the javax.script.ScriptEngineManager to execute arbitrary code via the Nashorn engine.
• Target System: The specific reference to cat confluence.cfg.xml indicates the primary objective is data exfiltration or reconnaissance of the Confluence database configuration file, which contains plaintext credentials.
• Obfuscation Technique: The use of URL encoding (20 for space, 28 for parenthesis, 27 for quotes) and hex encoding (7B, 7D for braces) is a standard technique to evade Web Application Firewalls (WAFs) and basic log filtering.
• Security Implication: Detection of this string in server logs or memory dumps is a High Severity (CVSS 9.0+) indicator of compromise, suggesting that an unauthenticated or authenticated attacker has achieved remote code execution (RCE).

Anatomical Breakdown of the Obfuscated String

To understand the threat, we must deconstruct the string layer by layer. The input string is a mix of literal characters and hexadecimal URL-encoded values. Below is the step-by-step decoding process.

Layer 1: Hexadecimal and URL Decoding

The string contains specific hex pairs that correspond to standard ASCII characters when URL-decoded:

• 7B → { (Open Brace)
• 20 → (Space)
• 28 → ( (Open Parenthesis)
• 29 → ) (Close Parenthesis)
• 27 → ' (Single Quote)
• 7D → } (Close Brace)

Layer 2: Reconstructed JavaScript Logic

Applying the decoding rules above to the core payload new javaxscriptScriptEngineManager2829getEngineByName2827nashorn2729eval2827cat20confluencecfgxml2729, we reconstruct the logical intent of the script:

new javax.script.ScriptEngineManager()
    .getEngineByName('nashorn')
    .eval('cat confluence.cfg.xml')

Analysis:

1. Engine Instantiation: The attacker instantiates a ScriptEngineManager. This class is part of the standard Java API for interacting with scripting engines.
2. Engine Selection: It specifically requests the nashorn engine. Nashorn is the default JavaScript engine in older Oracle JDK versions (Java 8/9). The reliance on this engine suggests the target server is running on an outdated JDK version where Nashorn is present and accessible.
3. Command Execution: The eval method is used to execute a string as a script. In this context, the string 'cat confluence.cfg.xml' is likely wrapped in a Runtime.getRuntime().exec() call within the actual payload, or the obfuscation hides the shell command wrapper. The command cat is a Unix/Linux utility used to output the contents of a file to standard output.

Vulnerability Vector and Attack Surface

This payload is typically injected into Confluence via Server-Side Template Injection (SSTI) or Remote Code Execution (RCE) vulnerabilities. Historically, Confluence has suffered from high-severity vulnerabilities allowing unauthenticated attackers to execute arbitrary code. Examples include CVE-2021-26084 and CVE-2022-26923.

The attacker chain usually follows this path:

1. Exploit a known vulnerability (e.g., a vulnerable template processor).
2. Inject a JavaScript engine context.
3. Use the JavaScript engine to call Java classes that allow shell command execution (ProcessBuilder or Runtime.exec).
4. Execute the cat command to exfiltrate sensitive configuration data.

The confluence.cfg.xml file is high-value intelligence because it contains:

• Database connection strings.
• Username and password for the Confluence database (often in plaintext or weakly encrypted).
• Internal network configuration details.

Data Comparison: Obfuscated vs. Deobfuscated Payloads

The following table compares the raw observed string with its functional equivalent to illustrate the obfuscation depth.

Component	Observed String Segment	Decoded/Logical Equivalent	Security Risk Level
Structure Opening	7B	{ (Object/Block start)	Low (Obfuscation)
Engine Call	new20javaxscript...	new javax.script... (Java Class instantiation)	Critical (RCE Potential)
Method Chaining	2829getEngineByName2827nashorn2729	().getEngineByName('nashorn')	High (Bypasses simple string filters)
Execution Logic	eval2827cat20confluencecfgxml2729	eval('cat confluence.cfg.xml') (Shell Command Exfil)	Critical (Data Breach/Recon)
Structure Closing	7D	} (Block end)	Low (Obfuscation)

Incident Response Checklist

If this string pattern is detected in your security logs, immediate action is required. Use the following checklist to manage the incident:

• Isolate the Host: Network segment the affected Confluence server to prevent lateral movement.
• Preserve Logs: Secure web server access logs, application logs, and system audit logs from the time of detection.
• Credential Rotation: Immediately rotate all database credentials, admin passwords, and API keys associated with the Confluence instance, assuming they are compromised.
• Patch Management: Apply the latest security patches to Confluence and upgrade the underlying JDK to a version where Nashorn is removed or deprecated (JDK 11+ removes Nashorn by default).
• Integrity Verification: Check the filesystem for unauthorized scripts, web shells, or modifications to confluence.cfg.xml.

Frequently Asked Questions

1. Why is the string URL-encoded instead of using standard hex encoding?

Standard hex encoding (e.g., turning 'n' into '