CVE-2021-41773: Critical Vulnerability in Apache HTTP Server

CVE-2021-41773 is a critical vulnerability in Apache HTTP Server 2.4.49 that allows attackers to exploit path traversal weaknesses. The issue arises from a flaw in path normalization, which can lead to unauthorized access to files outside designated directories. If the default configuration, which restricts access, is not enforced, attackers can map URLs to sensitive files and potentially execute remote code, especially if CGI scripts are enabled.

The vulnerability has been actively exploited in the wild, emphasizing the urgent need for organizations to address it. The criticality of this vulnerability is underscored by its CVSS score of 9.8, indicating an immediate threat to affected systems. Organizations using Apache HTTP Server 2.4.49 should prioritize patching to mitigate risks associated with this vulnerability.

The vulnerability is known to affect only Apache 2.4.49, and subsequent versions, such as Apache 2.4.50, have introduced fixes that were later found to be incomplete, as noted in CVE-2021-42013. Given the severity and potential impact, organizations are urged to patch the vulnerability immediately.

Organizations should assess their systems for the affected version and implement the necessary updates as outlined by the vendor to safeguard against this vulnerability.

Vulnerability Details

Technical Analysis

The root cause of CVE-2021-41773 is a flaw in how Apache HTTP Server 2.4.49 handles path normalization, allowing attackers to perform path traversal attacks. The attack vector is network-based, requiring no privileges or user interaction, making it easy for attackers to exploit. The attack complexity is low, meaning that even an unsophisticated attacker can leverage this vulnerability.

The impact of this vulnerability is serious, with a high confidentiality, integrity, and availability impact, as indicated by the CVSS score. It allows unauthorized access to files, which could lead to data breaches, service disruptions, or unauthorized remote code execution.

Risk & Impact Analysis

Risk to organizations includes unauthorized access to sensitive files and potential remote code execution. The blast radius is significant, as any organization utilizing Apache HTTP Server 2.4.49 could be affected. Given the CVSS score of 9.8 and the fact that it is actively exploited, organizations should prioritize patching immediately.

Exploitation Status

Affected Versions

The affected versions include Apache HTTP Server 2.4.49. Organizations should upgrade to a patched version, such as Apache HTTP Server 2.4.50 or later, to mitigate the vulnerability.

Mitigation & Remediation

Organizations should apply the vendor's patches immediately to remediate CVE-2021-41773. In cases where immediate patching is not feasible, it is recommended to enforce strict access controls and disable CGI scripts for the affected paths.

Detection Guidance

Security teams should monitor logs for unusual access patterns and file requests that may indicate exploitation attempts. Behavioral anomalies such as unexpected remote code execution should also be investigated promptly.

AppSecure Threat Intelligence Insight

The long-term significance of CVE-2021-41773 highlights the ongoing challenges in web application security. Organizations should review their security posture and consider regular security assessments to identify and mitigate similar vulnerabilities.

For comprehensive security practices, organizations may refer to resources such as the penetration testing methodology and the importance of a robust vulnerability management program.

Organizations should also consider engaging in vulnerability management programs to stay ahead of emerging threats and ensure that all systems are adequately protected.

Lastly, organizations looking to enhance their security posture may benefit from API security best practices and advanced threat detection techniques.