# CVE-2021-42013: Apache Web Server - Path Traversal

> Live exploitation tracking for CVE-2021-42013 by the CrowdSec Live Exploit Tracker, built from real-world attack data crowdsourced from CrowdSec's global network.

Page: https://tracker.crowdsec.net/cves/CVE-2021-42013

## Key facts

- **Exploitation phase:** Background Noise. Continuous low-level scanning or exploitation attempts are observed, mostly opportunistic and automated.
- **CVSS score:** 9.8
- **Public exploit available:** Yes
- **Affected products:** Apache HTTP Server
- **Weaknesses:** CWE-22 (Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'))
- **Tags:** web_server

## Description

It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue only affects Apache 2.4.49 and Apache 2.4.50 and not earlier versions.

## CrowdSec analysis

[CVE-2021-42013](https://euvd.enisa.europa.eu/vulnerability/CVE-2021-42013) is a critical vulnerability in the Apache HTTP Server that enables attackers to exploit insufficient fixes for prior path traversal issues, potentially accessing files outside the expected directories and executing arbitrary code if CGI scripts are enabled.

CrowdSec has been tracking this vulnerability and its exploits since 11th of October 2021.

CrowdSec network data shows that most actors exploiting CVE-2021-42013 rely on broad, untargeted scans with minimal filtering. The activity is largely automated and opportunistic in nature.
In addition, according to the CrowdSec network, attack volume against CVE-2021-42013 has dipped slightly compared to the previous week. Although still commonly targeted, the decline suggests a cooling-off period. Long-term relevance remains, but attention is waning.

Exploitation attempts typically focus on path traversal through specially crafted URLs, aiming to access unauthorized files or execute scripts on vulnerable systems.

## Timeline

- 2021-10-07: CVE Published. CVE-2021-42013 is published to NVD.
- 2021-10-11: Rule Released. CrowdSec releases a rule to detect CVE-2021-42013 exploitation attempts against the CrowdSec Network.
- 2021-10-11: CrowdSec First Seen. CrowdSec observes in-the-wild exploitation of CVE-2021-42013 for the first time.
- 2021-11-03: CISA KEV. CVE-2021-42013 is added to the Known Exploited Vulnerabilities catalog by CISA.
- 2021-11-17: CISA Remediation Deadline. Expiration of the CISA remediation deadline as described in [BOD 22-01](https://www.cisa.gov/news-events/directives/bod-22-01-reducing-significant-risk-known-exploited-vulnerabilities).

## References

- https://httpd.apache.org/security/vulnerabilities_24.html
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-42013.yaml

## Live exploitation data

The [Live Exploit Tracker page](https://tracker.crowdsec.net/cves/CVE-2021-42013) follows observed exploitation activity for CVE-2021-42013. [Request an API key](https://tracker.crowdsec.net/request-api-key) for full access to its exploitation timeline, attacking IP addresses and blocklists.