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How the Mentioned CVE Works:
CVE-2021-41773 is a critical vulnerability in Apache HTTP Server versions 2.4.49. It arises due to improper path normalization in the `ap_normalize_path()` function. Attackers can exploit this flaw by sending crafted HTTP requests to access files outside the document root directory. If the server is configured with “require all denied” missing, the attacker can execute arbitrary code on the server. This vulnerability is particularly dangerous because it allows remote code execution (RCE) without authentication, making it a high-severity threat.
DailyCVE Form:
Platform: Apache HTTP Server
Version: 2.4.49
Vulnerability: Path Traversal
Severity: Critical
Date: 2021-10-05
What Undercode Say:
Exploitation:
1. Crafting the Payload:
Attackers can send a malicious HTTP request like:
GET /icons/.%%32%65/.%%32%65/.%%32%65/.%%32%65/etc/passwd HTTP/1.1 Host: vulnerable-server
This bypasses path normalization and accesses sensitive files.
2. Remote Code Execution:
If mod_cgi is enabled, attackers can execute commands:
GET /cgi-bin/.%%32%65/.%%32%65/.%%32%65/.%%32%65/bin/sh HTTP/1.1 Host: vulnerable-server
Protection:
1. Update Apache:
Upgrade to Apache HTTP Server 2.4.50 or later.
sudo apt update && sudo apt install apache2
2. Configuration Check:
Ensure “require all denied” is set in the configuration:
<Directory /> Require all denied </Directory>
3. Web Application Firewall (WAF):
Deploy a WAF to filter malicious requests.
4. Log Monitoring:
Monitor logs for unusual activity:
tail -f /var/log/apache2/access.log
5. Patch Verification:
Verify the patch is applied:
httpd -v
6. Disable Unused Modules:
Disable mod_cgi if not required:
sudo a2dismod cgi
7. Network Segmentation:
Restrict access to Apache servers using firewalls.
8. Exploit Detection:
Use intrusion detection systems (IDS) to detect exploitation attempts.
9. Automated Tools:
Use vulnerability scanners like Nessus or OpenVAS to identify unpatched systems.
10. Incident Response:
Have a response plan in place for potential breaches.
By following these steps, organizations can mitigate the risks associated with CVE-2021-41773 and protect their Apache HTTP Server instances from exploitation.
References:
Reported By: https://www.cve.org/CVERecord?id=CVE-2025-30066
Extra Source Hub:
Undercode
