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How the CVE Works:
CVE-2021-41773 is a critical vulnerability in Apache HTTP Server 2.4.49 that allows path traversal and remote code execution due to improper path normalization. Attackers can exploit a flaw in the `ap_normalize_path()` function to bypass security checks and access files outside restricted directories. If `mod_cgi` is enabled, malicious actors can execute arbitrary commands by sending crafted HTTP requests. The issue arises when URLs contain encoded characters (like `%2e` for .), allowing traversal into unintended directories. A simple GET or POST request with a manipulated path can lead to unauthorized file disclosure or system compromise.
DailyCVE Form:
Platform: Apache HTTP Server
Version: 2.4.49
Vulnerability: Path Traversal & RCE
Severity: Critical
Date: 2021-10-05
Prediction: Patch expected by 2021-10-07
What Undercode Say:
Analytics:
- Exploits surged within 48 hours of disclosure.
- Mostly targets cloud-hosted Apache servers.
- Over 100,000 vulnerable instances detected pre-patch.
Exploit Commands:
curl -v "http://target.com/cgi-bin/.%2e/%2e%2e/%2e%2e/etc/passwd"
import requests
r = requests.get("http://target.com/icons/.%%32%65/.%%32%65/.%%32%65/etc/shadow")
print(r.text)
Mitigation Commands:
Immediate fix: sudo apt-get update && sudo apt-get upgrade apache2
Config hardening (httpd.conf): <Directory "/"> Require all denied </Directory>
Detection Script:
import os
def check_apache_version():
stream = os.popen('apache2 -v')
output = stream.read()
if "2.4.49" in output:
print("VULNERABLE")
Patch Verification:
httpd -v | grep "2.4.5"
WAF Rule (ModSecurity):
SecRule REQUEST_URI "@contains %2e" "deny,log,msg:'CVE-2021-41773 Exploit Attempt'"
Log Monitoring:
grep -E '..|%2e' /var/log/apache2/access.log
Impact:
- Unauthenticated RCE on misconfigured servers.
- Data leaks via `/etc/passwd` or web root files.
Post-Patch Actions:
- Audit all CGI-enabled endpoints.
- Disable `mod_cgi` if unused.
Sources:
Reported By: www.cve.org
Extra Source Hub:
Undercode
