CVE-2019-13647 in Firefly III
Summary
by MITRE
Firefly III before 4.7.17.3 is vulnerable to stored XSS due to lack of filtration of user-supplied data in image file content. The JavaScript code is executed during attachments/view/$file_id$ attachment viewing.
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Analysis
by VulDB Data Team • 08/05/2024
Firefly III version 4.7.17.2 and earlier contains a stored cross-site scripting vulnerability that arises from insufficient input validation of user-supplied data within image file content. This vulnerability exists in the attachment viewing functionality where the application fails to properly sanitize or escape user-provided content before rendering it in the browser context. When a user accesses an attachment through the attachments/view/$file_id$ endpoint, the application processes the image file content without adequate filtration, allowing malicious JavaScript code embedded within the image metadata or file structure to execute in the context of other users who view the attachment.
The technical flaw stems from a failure to implement proper content sanitization mechanisms for file uploads, particularly images that may contain embedded metadata or code structures. This represents a classic stored XSS vulnerability where the malicious payload is persisted in the application's database or file system and executed whenever the compromised content is retrieved and displayed. The vulnerability allows attackers to inject malicious scripts that can execute in the browser context of other users, potentially leading to session hijacking, credential theft, or further exploitation of the application environment.
The operational impact of this vulnerability extends beyond simple script execution as it provides attackers with the capability to establish persistent access to user sessions and potentially escalate privileges within the Firefly III application. The vulnerability affects all users who have access to the attachment viewing functionality, making it particularly dangerous in multi-user environments where users may view various file attachments. Attackers could craft malicious image files that contain embedded JavaScript payloads designed to steal cookies, redirect users to malicious domains, or perform actions on behalf of authenticated users.
Security practitioners should implement input validation and output encoding mechanisms to prevent this vulnerability from being exploited. The recommended mitigation involves sanitizing all user-supplied content, particularly image files, before storage and rendering. This includes implementing proper content type checking, metadata sanitization, and ensuring that all rendered content is properly escaped before display. The vulnerability aligns with CWE-79 which defines cross-site scripting as a critical web application security weakness, and represents a specific implementation gap that enables persistent script injection in file handling components. Organizations should also consider implementing web application firewalls and content security policies to provide additional layers of protection against such attacks.
The remediation approach should focus on upgrading to Firefly III version 4.7.17.3 or later where the vulnerability has been addressed through proper input validation and sanitization of attachment content. Additionally, implementing proper access controls and user education regarding file attachment security can help reduce the risk of exploitation. Security monitoring should include detection of unusual attachment access patterns and content modifications that may indicate exploitation attempts. This vulnerability demonstrates the importance of validating and sanitizing all user-provided content, particularly in file handling components, as highlighted in the ATT&CK framework under techniques related to web application exploitation and credential access through malicious file attachments.