CVE-2023-34448 in Grav
Summary
by MITRE • 06/15/2023
Grav is a file-based Web platform. Prior to version 1.7.42, the patch for CVE-2022-2073, a server-side template injection vulnerability in Grav leveraging the default `filter()` function, did not block other built-in functions exposed by Twig's Core Extension that could be used to invoke arbitrary unsafe functions, thereby allowing for remote code execution. A patch in version 1.74.2 overrides the built-in Twig `map()` and `reduce()` filter functions in `system/src/Grav/Common/Twig/Extension/GravExtension.php` to validate the argument passed to the filter in `$arrow`.
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Analysis
by VulDB Data Team • 07/13/2023
The vulnerability CVE-2023-34448 represents a critical server-side template injection flaw in the Grav web platform that emerged from an incomplete patch for a previous vulnerability. This issue affects versions prior to 1.7.42 and demonstrates how security patches can sometimes leave residual attack surfaces when not thoroughly addressing all potential exploitation vectors. The original CVE-2022-2073 was a server-side template injection vulnerability that leveraged the default filter() function in Twig, which is a powerful templating engine used by Grav. However, the initial patch failed to account for other built-in functions within Twig's Core Extension that could be exploited to achieve similar outcomes. This oversight created a dangerous situation where attackers could still exploit the system through alternative pathways that bypassed the original mitigation efforts.
The technical flaw stems from the incomplete restriction of built-in Twig functions within the Grav platform's template processing pipeline. When Grav processes templates, it uses Twig's Core Extension which exposes several functions including map() and reduce() that can be manipulated to execute arbitrary code. These functions are particularly dangerous because they allow for functional programming patterns that can be weaponized to call unsafe operations. The vulnerability specifically affects the way Grav handles user input within template contexts, where unvalidated input can flow into these filter functions and execute malicious payloads. This represents a classic case of insufficient input validation and function whitelisting, where the security controls were too permissive in allowing potentially dangerous operations to proceed. The vulnerability is categorized under CWE-94 - Improper Control of Generation of Code and aligns with ATT&CK technique T1059.007 - Command and Scripting Interpreter: Python, demonstrating how template injection vulnerabilities can lead to full system compromise through arbitrary code execution.
The operational impact of this vulnerability is severe and far-reaching for any organization using affected versions of Grav. Remote code execution capabilities allow attackers to completely compromise the web server hosting Grav installations, potentially leading to data breaches, system takeover, and lateral movement within network environments. The vulnerability affects not only the web application itself but also any underlying infrastructure that depends on Grav for content management or web delivery. Organizations with multiple Grav installations across different environments face significant risk exposure, as the vulnerability can be exploited through various attack vectors including user input fields, API endpoints, or configuration parameters that are processed through the template engine. The exploitability of this vulnerability is particularly concerning because it requires minimal user interaction and can be automated, making it a prime target for mass exploitation campaigns. The vulnerability also impacts the platform's integrity and availability, as successful exploitation can lead to complete system compromise and potential denial of service conditions.
The patch implemented in version 1.7.42 specifically addresses this vulnerability by overriding the map() and reduce() filter functions within the GravExtension.php file located at system/src/Grav/Common/Twig/Extension/GravExtension.php. This mitigation strategy involves validating the arguments passed to these filter functions through the $arrow parameter, effectively preventing the execution of arbitrary code through these pathways. The solution represents a defensive programming approach that focuses on function-level restrictions rather than attempting to block all potentially dangerous operations. The patch demonstrates the importance of comprehensive vulnerability assessment and the need for thorough testing of security patches to ensure that all potential attack vectors are addressed. Organizations should implement immediate patching of affected systems and conduct thorough security assessments to verify that no other similar vulnerabilities exist within their Grav installations. Additionally, the mitigation approach aligns with security best practices for template engine security and provides a model for addressing similar issues in other platforms that rely on similar templating technologies. The solution also emphasizes the importance of maintaining up-to-date security controls and the need for continuous monitoring of security advisories for affected software components.