CVE-2018-19789 in Symfony
Summary
by MITRE
An issue was discovered in Symfony 2.7.x before 2.7.50, 2.8.x before 2.8.49, 3.x before 3.4.20, 4.0.x before 4.0.15, 4.1.x before 4.1.9, and 4.2.x before 4.2.1. When using the scalar type hint `string` in a setter method (e.g. `setName(string $name)`) of a class that's the `data_class` of a form, and when a file upload is submitted to the corresponding field instead of a normal text input, then `UploadedFile::__toString()` is called which will then return and disclose the path of the uploaded file. If combined with a local file inclusion issue in certain circumstances this could escalate it to a Remote Code Execution.
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Analysis
by VulDB Data Team • 06/19/2023
This vulnerability exists in Symfony framework versions prior to specific patch releases, affecting multiple major versions including 2.7.x, 2.8.x, 3.x, 4.0.x, 4.1.x, and 4.2.x. The issue stems from improper handling of file uploads within form processing mechanisms when scalar type hints are used in setter methods. When developers implement type hinting with string parameters in form data classes, the framework's internal processing logic triggers unexpected behavior during file upload scenarios. The vulnerability specifically manifests when a form field that expects regular text input receives a file upload instead, creating a path disclosure condition through the UploadedFile::__toString() method invocation.
The technical flaw occurs at the intersection of form validation and file handling within Symfony's component architecture. When a form field with string type hinting receives file data, the framework's internal mechanisms call the UploadedFile::__toString() method which intentionally exposes the absolute file path of the uploaded file. This path disclosure represents a significant information disclosure vulnerability classified under CWE-200, as it reveals sensitive filesystem information that could aid attackers in subsequent exploitation attempts. The vulnerability is particularly dangerous because it can be leveraged in combination with other weaknesses, specifically local file inclusion vulnerabilities that exist in certain application contexts.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more severe attacks including remote code execution. Attackers can exploit the disclosed file paths to construct local file inclusion payloads that may lead to arbitrary code execution on the server. This escalation pathway aligns with ATT&CK technique T1505.003 for Server Software Component Vulnerabilities and demonstrates how seemingly minor information disclosure issues can compound into critical security breaches. The vulnerability affects applications that implement form handling with scalar type hints and file upload capabilities, making it prevalent across numerous Symfony-based web applications.
The recommended mitigations include upgrading to the patched versions of Symfony framework, specifically versions 2.7.50, 2.8.49, 3.4.20, 4.0.15, 4.1.9, and 4.2.1 or later. Organizations should also implement proper input validation and sanitization measures to prevent unexpected file upload scenarios in form processing. Additional defensive measures include restricting file upload capabilities, implementing proper access controls for uploaded files, and ensuring that form field validation properly distinguishes between different data types. Security teams should also monitor for potential exploitation attempts through log analysis and implement network-based intrusion detection systems to identify suspicious file path disclosure patterns. The vulnerability highlights the importance of comprehensive testing for edge cases in form handling and file upload scenarios, particularly when type hinting is employed in data class setters.