The Apache HTTP Server CVE-2021-41773 vulnerability affects versions 2.4.49 and 2.4.50, enabling remote attackers to perform path traversal attacks, potentially allowing access to files outside the document root.
It can expose sensitive information and execute arbitrary code if certain conditions are met. Exploits leveraging this vulnerability have been observed in the wild, prompting urgent security advisories.
Attackers can manipulate URL paths to access and potentially execute unauthorized files on the server, circumventing security measures that typically protect against such intrusions.
The vulnerability arises from inadequate path normalization in the Apache HTTP Server, which fails to correctly sanitize URLs containing encoded characters, allowing attackers to bypass security restrictions by crafting specially formatted requests, leading to unauthorized file access.
If the server configuration does not explicitly deny access to sensitive files, the attack can succeed, posing a significant risk to the confidentiality, integrity, and availability of data hosted on the server.
In addition to unauthorized file access, the vulnerability also affects interpreted files, such as CGI scripts, potentially leaking their source code, which can reveal critical details about the server’s configuration, internal logic, and other security-sensitive information, further compounding the risk.
Exploiting this vulnerability requires knowledge of the file system layout, but attackers often use automated tools to discover and exploit such weaknesses efficiently.
The active exploitation of CVE-2021-41773 in the wild underscores the need for immediate remediation, where administrators are strongly advised to upgrade to Apache HTTP Server version 2.4.51 or later, which includes patches that address this vulnerability.
Additionally, implementing stringent access controls, proper server configuration, and regular security audits can help mitigate the risk of similar vulnerabilities in the future.
Administrators should ensure that directory listings are disabled, access to sensitive directories is restricted, and URL normalization is correctly implemented, while regularly reviewing and updating server configurations based on the latest security advisories is crucial for maintaining a robust security posture.
Leveraging security tools such as Web Application Firewalls (WAFs) can provide an additional layer of defense against path traversal attacks and other web-based threats.
In order to find and fix vulnerabilities before malicious actors can exploit them, organizations should also conduct thorough penetration testing.
According to Broadcom, CVE-2021-41773 represents a critical security vulnerability in Apache HTTP Server that allows for path traversal and potential arbitrary code execution, and immediate patching and adherence to security best practices are essential to protect against active exploitation and safeguard sensitive data hosted on affected servers.
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