CVE-2020-5274 in Symfony
Summary
by MITRE
In Symfony before versions 5.0.5 and 4.4.5, some properties of the Exception were not properly escaped when the `ErrorHandler` rendered it stacktrace. In addition, the stacktrace were displayed even in a non-debug configuration. The ErrorHandler now escape alls properties of the exception, and the stacktrace is only display in debug configuration. This issue is patched in symfony/http-foundation versions 4.4.5 and 5.0.5
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Analysis
by VulDB Data Team • 05/10/2025
The vulnerability described in CVE-2020-5274 affects the Symfony framework versions prior to 5.0.5 and 4.4.5, specifically within the ErrorHandler component responsible for rendering exception stacktraces. This issue represents a classic information disclosure vulnerability where sensitive system information could be exposed to unauthorized users through improper sanitization of exception data. The flaw occurs during the rendering process when exceptions are displayed to users, creating potential attack vectors for malicious actors seeking to gather system intelligence.
The technical implementation of this vulnerability stems from inadequate input validation and output escaping mechanisms within Symfony's error handling system. When exceptions occurred within the application, the ErrorHandler component would render stacktrace information without properly escaping sensitive properties of the exception objects. This failure to sanitize exception data creates a path for cross-site scripting attacks and information disclosure scenarios where attackers could potentially extract system paths, configuration details, or other sensitive data from the stacktrace output. The vulnerability is categorized under CWE-79 as it involves improper neutralization of input during web page generation, and aligns with ATT&CK technique T1211 for exploitation of information disclosure vulnerabilities.
The operational impact of this vulnerability extends beyond simple information exposure, as it affects the fundamental security posture of Symfony applications. Attackers could leverage this flaw to gather detailed information about the application's internal structure, including file paths, class names, and potentially sensitive configuration parameters. The fact that stacktraces were displayed even in non-debug configurations represents a critical misconfiguration that violates security best practices for production environments. This behavior effectively provides attackers with a roadmap for further exploitation attempts, making the application more vulnerable to subsequent attacks.
The fix implemented in Symfony versions 4.4.5 and 5.0.5 addresses both aspects of the vulnerability by enforcing proper escaping of all exception properties and restricting stacktrace display to debug configurations only. This remediation aligns with security principles outlined in OWASP Top 10 and follows the principle of least privilege by ensuring that sensitive debugging information is only accessible in controlled development environments. Organizations should prioritize updating their Symfony installations to these patched versions to eliminate the risk of information disclosure and potential exploitation. The mitigation strategy also emphasizes the importance of proper error handling configuration in production environments, where detailed error messages should never be exposed to end users to prevent attackers from gaining insights into the application's architecture and potential attack surfaces.