CVE-2021-41567 in Tad Uploader
Summary
by MITRE • 10/08/2021
The new add subject parameter of Tad Uploader view book list function fails to filter special characters. Unauthenticated attackers can remotely inject JavaScript syntax and execute stored XSS attacks.
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Analysis
by VulDB Data Team • 10/14/2021
The vulnerability identified as CVE-2021-41567 resides within the Tad Uploader web application, specifically affecting the view book list function that includes a new add subject parameter. This weakness represents a critical security flaw that allows unauthenticated attackers to exploit stored cross-site scripting vulnerabilities through improper input validation and sanitization. The vulnerability manifests when the application fails to adequately filter or escape special characters in the subject parameter, creating an avenue for malicious code injection that persists in the application's data storage.
The technical implementation of this vulnerability stems from inadequate input validation mechanisms within the Tad Uploader's subject parameter handling. When users submit book listings through the view book list function, the application processes the subject field without proper sanitization of potentially dangerous characters such as angle brackets, quotation marks, or script tags. This lack of proper input filtering creates a persistent XSS vector where attacker-controlled JavaScript code can be stored in the application's database and subsequently executed whenever the affected page is rendered to other users. The vulnerability is classified as stored XSS under CWE-79, which specifically addresses the scenario where malicious scripts are stored on the server and executed in the context of other users' browsers.
From an operational perspective, this vulnerability poses significant risks to both application integrity and user security. Unauthenticated attackers can leverage this flaw to execute arbitrary JavaScript code within the context of other users' sessions, potentially leading to session hijacking, credential theft, or redirection to malicious websites. The stored nature of the vulnerability means that once exploited, the malicious payload remains active until manually removed from the application's data store, creating a persistent threat that can affect multiple users over extended periods. The impact extends beyond individual user compromise to potentially enable broader attack vectors including privilege escalation or data exfiltration, particularly if the application handles sensitive user information or administrative functions.
The exploitation of CVE-2021-41567 aligns with ATT&CK technique T1566.001 for initial access through malicious links or files, and T1059.001 for command and control through script injection. Organizations should implement immediate mitigations including input validation and output encoding for all user-supplied data, particularly parameters that are rendered in web pages. The solution involves implementing comprehensive sanitization routines that strip or encode dangerous characters before storing user input, combined with proper HTML escaping mechanisms when rendering content to browsers. Additionally, the application should employ Content Security Policy headers to limit script execution and implement proper access controls to prevent unauthorized data modification. Regular security testing and input validation audits should be conducted to prevent similar vulnerabilities from emerging in other application components, as this flaw demonstrates the critical importance of sanitizing all user inputs in web applications. The vulnerability represents a clear violation of secure coding practices and emphasizes the necessity of defense-in-depth strategies including proper input validation, output encoding, and regular security assessments to maintain application resilience against common web-based attack vectors.