CVE-2021-20111 in TCExam
Summary
by MITRE • 07/30/2021
A stored cross-site scripting vulnerability exists in TCExam
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/05/2021
The stored cross-site scripting vulnerability in TCExam represents a critical security flaw that allows attackers to inject malicious scripts into the application's database, which are then executed when other users view the affected content. This vulnerability stems from inadequate input validation and output sanitization mechanisms within the TCExam platform, which is commonly used for online examination systems in educational institutions and corporate training environments. The flaw enables persistent XSS attacks where malicious code can be stored in the application's database and executed in the context of other users' browsers, potentially leading to unauthorized access, session hijacking, or data exfiltration.
The technical implementation of this vulnerability occurs when TCExam fails to properly sanitize user inputs before storing them in the database, particularly in fields that are later rendered in web pages without adequate escaping or encoding. Attackers can exploit this by submitting malicious script payloads through forms, comment sections, or any input field that accepts user content and displays it to other users. When legitimate users browse pages containing the stored malicious content, their browsers execute the injected scripts, which can perform actions such as stealing session cookies, redirecting users to malicious sites, or modifying page content to deceive users. This type of vulnerability falls under CWE-79 which specifically addresses cross-site scripting flaws in web applications.
The operational impact of this vulnerability extends beyond simple data theft, as it can compromise the integrity of entire examination systems and undermine the trust placed in online testing platforms. Educational institutions relying on TCExam for critical assessments face potential risks including exam cheating through script injection, unauthorized access to student records, and disruption of academic integrity. Corporate training environments may experience similar threats where confidential training materials or employee assessment data could be compromised. The persistent nature of stored XSS means that once exploited, the malicious scripts continue to execute until manually removed from the database, providing attackers with extended periods of access to target systems. This vulnerability aligns with ATT&CK technique T1566.001 which covers the use of malicious content to gain initial access through phishing attacks, as attackers can leverage this flaw to compromise user sessions and escalate privileges within the examination environment.
Mitigation strategies for this vulnerability should include comprehensive input validation and output encoding mechanisms throughout the TCExam application, implementing proper content security policies, and regularly updating the platform to address known security flaws. Organizations should conduct thorough security assessments of their TCExam installations, implement web application firewalls to detect and block malicious script injections, and establish regular monitoring procedures to identify and remove stored malicious content. Additionally, user education about the risks of clicking suspicious links or submitting untrusted content to examination systems can help reduce exploitation success rates. The vulnerability highlights the importance of following secure coding practices and implementing defense-in-depth strategies to protect web applications from persistent XSS threats that can compromise entire user bases.