CVE-2022-0323: Mustache Template Engine XSS Vulnerability

CVE-2022-0323 Overview

CVE-2022-0323 is a template engine injection vulnerability affecting mustache/mustache, a popular PHP implementation of the Mustache templating language. The vulnerability stems from improper neutralization of special elements used in the template engine, specifically related to section names. This flaw allows attackers with low-privilege access to inject malicious content through template sections, potentially leading to code injection attacks.

Critical Impact

Successful exploitation of this vulnerability could allow attackers to achieve high impact on confidentiality, integrity, and availability of affected systems through template injection attacks.

Affected Products

• Mustache.php (mustache/mustache) versions prior to 2.14.1
• PHP applications using vulnerable versions of the Mustache Packagist package
• Web applications integrating mustache/mustache for templating functionality

Discovery Timeline

• 2022-01-21 - CVE-2022-0323 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-0323

Vulnerability Analysis

The vulnerability exists in the Mustache template compiler component, specifically in how section names are processed and rendered. The core issue involves improper neutralization (CWE-1336) of special elements within template section names, which can lead to code injection (CWE-94) scenarios.

When Mustache.php compiles templates, it generates PHP code that processes template sections. The vulnerable code path included section names directly in comments within the generated code without proper sanitization. This oversight could allow an attacker to break out of the comment context and inject arbitrary PHP code into the compiled template output.

The attack requires network access and low-privilege authentication to the target application, but once these conditions are met, exploitation requires no user interaction. The potential impact spans all three security domains: confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause lies in the src/Mustache/Compiler.php file where template sections are compiled. The original implementation included unsanitized section names in PHP comments within the generated code. By crafting a malicious section name containing PHP comment-closing sequences, an attacker could escape the comment context and inject executable code.

Attack Vector

The attack vector is network-based, requiring authenticated access to an application that allows user-controlled input to influence Mustache template section names. An attacker would craft a malicious template section name containing special characters designed to break out of the comment context and inject PHP code.

     }
 
     const SECTION_CALL = '
-        // %s section
         $value = $context->%s(%s);%s
         $buffer .= $this->section%s($context, $indent, $value);
     ';

Source: GitHub Commit

The patch removes the comment line that previously included the section name (// %s section), eliminating the injection point entirely. This prevents attackers from using section names to escape comment contexts and inject code.

Detection Methods for CVE-2022-0323

Indicators of Compromise

• Unusual or malformed Mustache template files with suspicious section names containing PHP syntax
• Error logs showing template compilation failures with unexpected characters
• Web application logs indicating template injection attempts with special characters like */ or <?php
• Unexpected PHP code execution originating from template rendering processes

Detection Strategies

• Implement dependency scanning to identify mustache/mustache versions prior to 2.14.1 in your PHP projects
• Use static analysis tools to detect user-controlled input flowing into Mustache template section names
• Monitor for anomalous template compilation patterns or unexpected code execution
• Review Composer lockfiles for vulnerable mustache/mustache package versions

Monitoring Recommendations

• Enable verbose logging for template compilation operations in production environments
• Set up alerts for template processing errors that may indicate exploitation attempts
• Implement web application firewall (WAF) rules to detect template injection patterns
• Monitor file integrity of compiled template caches for unauthorized modifications

How to Mitigate CVE-2022-0323

Immediate Actions Required

• Update mustache/mustache to version 2.14.1 or later immediately via Composer
• Audit applications for any user-controlled input that influences template section names
• Review recent template compilation logs for signs of exploitation attempts
• Consider temporarily disabling features that allow user-influenced template content if patching is delayed

Patch Information

The vulnerability was fixed in mustache/mustache version 2.14.1. The fix, implemented in commit 579ffa5c96e1d292c060b3dd62811ff01ad8c24e, removes the vulnerable comment pattern from the compiled section code, preventing section name content from being interpreted in a code context.

Additional technical details about the vulnerability and fix can be found in the Huntr Bounty Report.

Workarounds

• Implement strict input validation on any data that could influence template section names
• Use a content security policy (CSP) to limit the impact of potential code injection
• Deploy web application firewalls with rules targeting template injection patterns
• Sanitize all user input before it reaches the template rendering layer

# Update mustache/mustache via Composer
composer require mustache/mustache:^2.14.1

# Verify the installed version
composer show mustache/mustache | grep versions

# Clear any cached compiled templates
rm -rf storage/framework/views/*.php  # Laravel example
rm -rf cache/mustache/*                # Generic cache location