CVE-2021-20124

The local file inclusion vulnerability identified in the Draytek VigorConnect 1.6.0-B3 version poses a significant risk due to its ability to allow unauthorized access to sensitive files on the underlying operating system. This vulnerability arises from improper validation of user input within the file download functionality of the WebServlet endpoint. An attacker can manipulate the parameters sent to this endpoint, potentially leading to the inclusion of arbitrary files. The lack of authentication checks exacerbates the issue, as it permits unauthenticated users to exploit the vulnerability without needing valid credentials.

Exploitation of this vulnerability can occur through various attack vectors. An attacker could craft a malicious request targeting the vulnerable endpoint, specifying the path of sensitive files on the server. For instance, by leveraging directory traversal techniques, the attacker can navigate the file system and access critical configuration files, logs, or even sensitive user data. This exploitation can be executed remotely, making it particularly dangerous. The attacker could also automate the process, scanning for vulnerable instances of the product and launching mass exploitation campaigns, thereby increasing the potential impact.

The real-world implications of this vulnerability are profound, especially for organizations relying on Draytek VigorConnect for their networking needs. Successful exploitation could lead to unauthorized access to sensitive information, including system configurations and user credentials, which could further facilitate more extensive attacks, such as privilege escalation or lateral movement within the network. The business risks associated with such breaches include reputational damage, financial losses due to remediation efforts, and potential legal ramifications stemming from data protection regulations. Organizations could face significant operational disruptions as they respond to incidents and mitigate the fallout from data exposure.

To detect and mitigate this vulnerability, organizations should implement a multi-layered security approach. Regular vulnerability assessments and penetration testing can help identify instances of the affected product within the network. Additionally, monitoring logs for unusual access patterns or unauthorized file downloads can serve as an early warning system for potential exploitation attempts. From a mitigation standpoint, applying patches or updates provided by the vendor is crucial. Furthermore, employing web application firewalls (WAFs) can help filter out malicious requests targeting the vulnerable endpoint. Organizations should also consider implementing strict access controls and file permissions to limit the potential impact of any exploitation.

In conclusion, the local file inclusion vulnerability in Draytek VigorConnect 1.6.0-B3 presents a serious threat that can lead to unauthorized access to sensitive files and data. The ease of exploitation and the potential for significant business impact necessitate immediate attention from organizations using this product. By adopting proactive detection and mitigation strategies, businesses can better protect themselves against the risks associated with this vulnerability, ensuring the integrity and confidentiality of their systems and data.

CSURFACE threat intelligence has identified a marked escalation in detection activity related to CVE-2021-20124, indicating renewed or increased adversary interest in exploiting the local file inclusion vulnerability within Draytek VigorConnect 1.6.0-B3. Although the EPSS score remains high and stable, suggesting persistent exploitability potential, the recent emergence of new sightings after a period of dormancy underscores a possible shift in attacker behavior or campaign focus. This development is significant for defenders as it signals that threat actors may be actively probing or attempting to leverage this vulnerability, potentially increasing the risk of unauthorized access to sensitive system files with elevated privileges. While no new exploit techniques or ransomware associations have been reported, the uptick in telemetry warrants heightened vigilance and prioritization of detection efforts. Consequently, the threat level should be considered elevated due to the combination of sustained exploitability and fresh adversary activity, reinforcing the criticality of monitoring and response capabilities for environments running the affected software.

Update 2 — June 19, 2026

CSURFACE threat intelligence has identified a marked escalation in detection activity related to CVE-2021-20124, indicating increased adversary interest and probing attempts targeting the DrayTek VigorConnect local file inclusion vulnerability. Although the EPSS score has declined moderately, reflecting a slight reduction in predicted exploit likelihood, the surge in telemetry suggests that threat actors continue to actively test or exploit this weakness in operational environments. This divergence underscores the importance of interpreting exploitability metrics alongside real-world activity signals. No new exploit techniques or ransomware affiliations have been observed, maintaining the current understanding of the threat landscape. However, the intensified detection frequency elevates the urgency for defenders to maintain robust monitoring and response postures. Consequently, the overall threat level should be considered heightened due to the combination of persistent exploitability and increased adversary engagement, signaling a sustained risk of unauthorized access to critical system files with elevated privileges.

Update 3 — July 16, 2026

CSURFACE threat intelligence has identified a slight increase in detection activity related to CVE-2021-20124, indicating a modest but consistent uptick in adversary engagement targeting the DrayTek VigorConnect vulnerability. While no new exploit techniques or ransomware affiliations have surfaced, this elevated detection frequency suggests that threat actors continue to probe and potentially exploit this local file inclusion flaw to access sensitive system files with root privileges. The persistence of this activity, despite stable exploitability scores, underscores the vulnerability’s ongoing attractiveness as an attack vector. For defenders, this trend highlights the necessity of sustained vigilance and reinforces the importance of monitoring for anomalous file access attempts within affected environments. Consequently, the risk level associated with CVE-2021-20124 should be regarded as moderately heightened due to the combination of enduring exploit potential and increased adversary probing, signaling a sustained threat to system integrity.