CVE-2022-37767: Pebble Templates Auth Bypass Vulnerability

CVE-2022-37767 Overview

CVE-2022-37767 is an authorization bypass vulnerability in Pebble Templates version 3.1.5 that allows attackers to circumvent protection mechanisms and achieve arbitrary code execution through the springbok component. This template injection vulnerability enables remote attackers to execute arbitrary Java code within the context of the application utilizing the Pebble templating engine.

It is important to note that the vendor disputes this vulnerability, stating that input to the Pebble templating engine is designed to include arbitrary Java code. According to the vendor, the responsibility for validating input lies with the application using the engine, not the engine itself. Applications should either prevent untrusted sources from providing input or implement appropriate restrictions.

Critical Impact

Remote attackers can bypass security protections to execute arbitrary code with full system compromise potential, affecting confidentiality, integrity, and availability of affected systems.

Affected Products

• Pebble Templates version 3.1.5

Discovery Timeline

• 2022-09-12 - CVE-2022-37767 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-37767

Vulnerability Analysis

This vulnerability is classified under CWE-863 (Incorrect Authorization), indicating that the Pebble Templates engine fails to properly enforce authorization checks when processing template input. The flaw resides in the template processing logic where attackers can leverage the springbok functionality to bypass intended security controls.

The vulnerability is network-exploitable without requiring authentication or user interaction, making it highly dangerous in environments where untrusted input can reach the template engine. When successfully exploited, attackers gain the ability to execute arbitrary Java code within the application's security context, potentially leading to complete system compromise.

Root Cause

The root cause of CVE-2022-37767 lies in improper authorization controls within the Pebble Templates engine when processing template expressions. The springbok component lacks adequate validation to prevent malicious code paths, allowing attackers to inject and execute arbitrary Java code. The engine processes template input with elevated privileges without properly restricting access to dangerous functionality.

The vendor's position is that applications integrating Pebble Templates should implement their own input validation since the engine is designed to execute Java code by nature. However, when applications fail to implement such restrictions, the lack of built-in safeguards enables exploitation.

Attack Vector

The attack vector is network-based, requiring attackers to supply malicious template input to an application using the vulnerable Pebble Templates library. The attack does not require authentication or user interaction. Attackers craft specially constructed template expressions that leverage the springbok functionality to bypass protection mechanisms.

The exploitation flow involves submitting malicious template content through any application interface that processes user-supplied templates. The injected code executes within the Java Virtual Machine context of the target application, providing attackers with the same privileges as the application itself.

For technical details on exploitation techniques, refer to the GitHub Web Security Issue and the vendor's response in the GitHub Issue Comment.

Detection Methods for CVE-2022-37767

Indicators of Compromise

• Unusual template processing requests containing suspicious Java class references or method invocations
• Unexpected process spawning or network connections originating from applications using Pebble Templates
• Log entries showing template parsing errors with class loading or reflection-related exceptions
• Evidence of code execution artifacts in application logs referencing springbok or unauthorized method calls

Detection Strategies

• Implement application-level logging to capture and analyze all template input before processing
• Deploy web application firewalls (WAF) configured to detect template injection patterns and suspicious Java code constructs
• Monitor for unusual class loading activity or reflection API usage within applications utilizing Pebble Templates
• Use runtime application self-protection (RASP) solutions to detect and block unauthorized code execution attempts

Monitoring Recommendations

• Establish baseline template processing patterns and alert on anomalous input characteristics
• Monitor application memory and process behavior for signs of injected code execution
• Configure SIEM alerts for template-related error patterns that may indicate exploitation attempts
• Review application access logs for patterns consistent with template injection reconnaissance or exploitation

How to Mitigate CVE-2022-37767

Immediate Actions Required

• Audit all applications using Pebble Templates 3.1.5 to identify potential exposure to untrusted template input
• Implement strict input validation and sanitization for any user-controlled template content before processing
• Consider restricting template sources to trusted origins only, preventing untrusted users from supplying template content
• Apply network segmentation to limit the blast radius if an application using Pebble Templates is compromised

Patch Information

The vendor disputes this as a vulnerability, maintaining that input validation is the responsibility of applications integrating the Pebble Templates engine. Organizations should consult the vendor's official response for guidance on secure implementation practices.

Applications using Pebble Templates should implement their own security controls to prevent untrusted input from reaching the template engine. Check for any updates to the Pebble Templates library that may include additional security hardening features.

Workarounds

• Restrict template input sources to trusted, authenticated users with appropriate authorization
• Implement a template allowlist that permits only known-safe template constructs to be processed
• Use sandboxing or containerization to isolate applications processing templates from critical infrastructure
• Deploy application-layer security controls such as input validation middleware to filter potentially malicious template content before it reaches the Pebble engine

# Example: Restrict Pebble Templates access to trusted sources only
# Ensure application configuration limits template processing to internal, validated sources

# 1. Review application code for user-controlled template inputs
grep -r "PebbleEngine\|getTemplate\|evaluate" ./src/

# 2. Implement input validation before template processing
# Add validation logic in your application's template handling code

# 3. Consider running applications using Pebble Templates in isolated containers
# with restricted network access and minimal privileges