CVE-2019-10909 in Symfony
Summary
by MITRE
In Symfony before 2.7.51, 2.8.x before 2.8.50, 3.x before 3.4.26, 4.x before 4.1.12, and 4.2.x before 4.2.7, validation messages are not escaped, which can lead to XSS when user input is included. This is related to symfony/framework-bundle.
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Analysis
by VulDB Data Team • 08/26/2025
The vulnerability identified as CVE-2019-10909 represents a critical cross-site scripting weakness in the Symfony web application framework that affects multiple major versions including 2.7.51, 2.8.50, 3.4.26, 4.1.12, and 4.2.7. This issue stems from insufficient output escaping of validation messages within the symfony/framework-bundle component, creating a pathway for malicious actors to inject arbitrary javascript code into web applications built on Symfony. The flaw specifically manifests when user input is processed through the framework's validation mechanisms and subsequently displayed in error messages without proper sanitization.
The technical nature of this vulnerability aligns with CWE-79, which categorizes cross-site scripting flaws as weaknesses in web applications that allow attackers to inject client-side scripts into web pages viewed by other users. The vulnerability occurs at the validation message rendering layer where the framework fails to properly escape special characters in user-supplied input before incorporating it into error messages displayed to end users. This creates an environment where malicious input containing javascript code can be executed in the context of other users' browsers, potentially leading to session hijacking, data theft, or further exploitation of the affected applications.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform various malicious activities including stealing user sessions, redirecting users to phishing sites, defacing web applications, or even establishing persistent backdoors through more sophisticated attack vectors. The widespread adoption of Symfony across enterprise applications means that organizations using affected versions are potentially exposed to these risks, particularly in applications that handle user input through forms, API endpoints, or any validation processes that might display user-supplied data in error messages. The vulnerability affects both the framework's core validation functionality and its bundle components, making it particularly dangerous as it can be exploited across multiple application types and deployment scenarios.
Organizations should immediately upgrade to the patched versions of Symfony as recommended by the framework maintainers, specifically moving to versions 2.7.51, 2.8.50, 3.4.26, 4.1.12, or 4.2.7 respectively. Additionally, implementing proper input validation and output escaping mechanisms at the application level can serve as a mitigating factor while awaiting the official patches. Security teams should conduct thorough vulnerability assessments of their Symfony-based applications to identify any custom code that might be vulnerable to similar issues, particularly in areas where user input is processed and displayed. The ATT&CK framework categorizes this type of vulnerability under the T1059.007 technique for "Command and Scripting Interpreter: JavaScript" as attackers can leverage the XSS flaw to execute javascript code in victim browsers, making it a critical concern for application security teams implementing defense-in-depth strategies.