What is CVE-2021-41773 vulnerability?
CVE-2021-41773 is a path traversal vulnerability in Apache HTTP Server 2.4.49 that allows attackers to map URLs to files located outside the expected document root. This critical flaw, when exploited, permits remote actors to view sensitive files or execute arbitrary code (in some cases) on vulnerable servers. Its primary risk lies in compromising data confidentiality, integrity, and availability, particularly for organizations using default configurations.
When was it discovered?
The vulnerability was disclosed on October 5, 2021. It was initially discovered by security researchers who submitted their findings to Apache's team. A follow-up patch for this vulnerability was quickly addressed, but some subsequent exploits continued against systems unpatched post-disclosure.
Affected products & versions
Product | Versions Affected | Fixed Versions / Patch Links |
Apache HTTP Server | 2.4.49 |
CVE-2021-41773 technical description
CVE-2021-41773 stems from insufficient input validation in Apache HTTP Server’s default configurations. Path traversal flaws allow unauthorized access to files outside the server’s public document structure, particularly when non-public directories lack proper protections.
Tactics, Techniques & Procedures (TTPs)
Attackers typically exploit the vulnerability by sending specially crafted GET requests that bypass normal file access restrictions, allowing traversal via encoded directory navigation patterns (“../../../”). Combined with other system weaknesses, this flaw can enable arbitrary file reads or remote code execution.
Indicators of compromise
Look out for unusual directory traversal requests in server access logs. Suspicious patterns, such as “../../../etc/passwd,” or repeated attempts to access sensitive configurations, often signal exploitation attempts. Ensure monitoring of unusual IPs, excessive failed requests, and unauthorized file activity.
Known proof-of-concepts & exploits
A public proof-of-concept (PoC) exploit has been released on platforms like GitHub, quickly incorporated into frameworks like Metasploit. Active exploitation campaigns targeting this vulnerability have been widely reported since its disclosure.
How to detect CVE-2021-41773 vulnerability
Detection can be performed using network-based intrusion detection systems (NIDS) for malicious traversal signatures. Analyze server access logs for exploitation patterns or deploy endpoint detection and response (EDR) solutions to identify unusual code execution or unauthorized file access. Sample SIEM queries should focus on HTTP requests containing encoded traversal strings.
Impact & risk of CVE-2021-41773 vulnerability
If unmitigated, this vulnerability poses critical business and technical risks. Exploits can expose sensitive data, configuration files, or enable system takeover via malicious scripts. For example, attackers gaining access to configuration files on a high-volume web server could lead to enterprise-wide outages or data breaches, damaging reputation and financial stability.
Mitigation & remediation strategies
To mitigate the CVE-2021-41773 vulnerability, upgrade affected Apache servers to 2.4.51 or later immediately. Apply proper access controls to all non-public directories and disable unnecessary modules to minimize risk exposure. To strengthen defenses, implement network segmentation and monitor critical server traffic for suspicious patterns.
CVE-2021-41773 Vulnerability FAQs
Protect What Matters
