CVE-2024-35226: Smarty Template Engine RCE Vulnerability

CVE-2024-35226 Overview

CVE-2024-35226 is a code injection vulnerability in Smarty, a widely-used template engine for PHP that facilitates the separation of presentation (HTML/CSS) from application logic. In affected versions, template authors could inject PHP code by choosing a malicious file name for an extends tag, allowing arbitrary code execution within the context of the PHP application.

Critical Impact

Template authors with the ability to create or modify templates can achieve arbitrary PHP code execution, potentially compromising the entire web application and underlying server. Sites that cannot fully trust template authors are at significant risk.

Affected Products

• Smarty Template Engine (versions prior to security patch)
• PHP applications utilizing vulnerable Smarty versions
• Content management systems and frameworks built on Smarty

Discovery Timeline

• 2024-05-28 - CVE CVE-2024-35226 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-35226

Vulnerability Analysis

This vulnerability is classified as CWE-94 (Improper Control of Generation of Code - Code Injection). The flaw exists in Smarty's handling of the extends tag, which is used for template inheritance. When processing an extends directive, Smarty fails to properly validate and sanitize the file name parameter, creating an injection point for malicious PHP code.

The attack requires an authenticated user with template authoring privileges, and some user interaction is involved in the exploitation chain. Upon successful exploitation, attackers can achieve both high confidentiality and integrity impact, potentially reading sensitive data and modifying application behavior, though availability is not directly impacted.

Root Cause

The root cause lies in insufficient input validation within Smarty's template parsing mechanism. When the extends tag processes a file name, it does not adequately sanitize special characters or validate the input against expected patterns. This allows specially crafted file names to break out of the intended context and inject executable PHP code into the template compilation process.

Attack Vector

The attack vector is network-based and requires low complexity to execute. An attacker with template authoring privileges can craft a malicious template file containing an extends tag with a specially formatted file name. When Smarty processes this template, the malicious payload embedded in the file name is executed as PHP code.

The vulnerability mechanism involves the extends tag file name parameter being improperly handled during template compilation. When a template author specifies a malicious file name pattern, the parser fails to properly escape or validate the input, allowing PHP code to be injected and subsequently executed. For detailed technical information, refer to the GitHub Security Advisory.

Detection Methods for CVE-2024-35226

Indicators of Compromise

• Unexpected PHP errors or exceptions related to template processing or extends tag evaluation
• Unusual file access patterns in template directories, particularly files with suspicious naming conventions
• Web server logs showing template compilation errors followed by unauthorized actions
• New or modified template files containing unusual extends tag syntax

Detection Strategies

• Implement file integrity monitoring on template directories to detect unauthorized modifications
• Review template files for suspicious extends tag patterns containing special characters or encoded sequences
• Monitor PHP error logs for Smarty-related exceptions that may indicate exploitation attempts
• Audit template authoring permissions and review which users have write access to template files

Monitoring Recommendations

• Enable verbose logging for Smarty template compilation events
• Configure intrusion detection systems to alert on PHP code execution patterns originating from template directories
• Implement real-time alerting for new template file creation or modification by non-administrative users
• Monitor outbound network connections from web servers that may indicate post-exploitation activity

How to Mitigate CVE-2024-35226

Immediate Actions Required

• Update Smarty to the latest patched version immediately using the commit referenced in the security advisory
• Audit all existing templates for potentially malicious extends tag usage
• Restrict template authoring privileges to only fully trusted users
• Consider implementing a template review workflow for any template changes

Patch Information

The vulnerability has been addressed in an official security patch. The fix is available in commit 0be92bc8a6fb83e6e0d883946f7e7c09ba4e857a. Users should update to the latest Smarty version that includes this patch. For detailed patch information, see the GitHub Commit. Debian users should also review the Debian LTS Announcement for distribution-specific guidance.

Important: There is no patch available for users on the v3 branch. Users on this branch should consider upgrading to a newer major version.

Workarounds

• There are no known workarounds for this vulnerability according to the security advisory
• As a risk reduction measure, limit template authoring access to only fully trusted personnel
• Consider implementing a sandboxed template environment with restricted PHP functions if possible
• Review and harden file system permissions on template directories to prevent unauthorized modifications

# Update Smarty via Composer to get the latest security patch
composer update smarty/smarty

# Verify installed version after update
composer show smarty/smarty | grep versions

# Audit template files for suspicious extends tag patterns
grep -r "{extends" /path/to/templates/ | grep -E "['\"].*[^a-zA-Z0-9_\-\./]"