Known exploited vulnerability · CISA KEV

CVE-2021-42013: Apache HTTP Server Path Traversal Vulnerability

Apache HTTP Server contains a path traversal vulnerability that allows an attacker to perform remote code execution if files outside directories configured by Alias-like directives are not under default require all denied or if CGI scripts are enabled. This CVE ID resolves an incomplete patch for CVE-2021-41773.

CVE-2021-42013

Exploited in the wild. Fix this first.

CISA added it to the Known Exploited Vulnerabilities catalog on 2021-11-03: attackers are using it right now. It is known to be used in ransomware campaigns.

CISA KEV: Listed; Added 2021-11-03 · federal fix-by 2021-11-17
EPSS (30 days): over 99.9%; Higher than 99.9% of CVEs · 2026-11-01
CVSS v3.1: 9.8 Critical; CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

What CISA says

Apache HTTP Server Path Traversal Vulnerability

Apply updates per vendor instructions.

NVD description · published 2021-10-07

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.

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How to check if you are exposed to CVE-2021-42013

Find every Apache HTTP Server system you or your clients run, including ones exposed to the internet. Those come first: CISA only lists flaws attackers are already using.
Compare each version with the fixed versions in the vendor advisory. Where no fix exists yet, apply the vendor’s mitigation or take the system off the internet.
Run a credentialed vulnerability scan to catch the systems you missed, then check that the next scan no longer reports CVE-2021-42013.

US federal agencies had to fix this by 2021-11-17. Everyone else should treat that deadline as a guide: if it has passed, this is overdue.

Affected versions

Versions the National Vulnerability Database lists as vulnerable to CVE-2021-42013. Check the vendor advisory for the exact fixed builds before you sign anything off.

Product	Vulnerable versions
Apache Http Server	2.4.49; 2.4.50
Fedoraproject Fedora	34; 35
Oracle Instantis Enterprisetrack	17.1; 17.2; 17.3
Oracle JD Edwards Enterpriseone Tools	before 9.2.6.0
Oracle Secure Backup	before 18.1.0.1.0
Netapp Cloud Backup	all versions

Timeline

2021-10-07 · Published in the National Vulnerability Database
2021-11-03 · Added to CISA's Known Exploited Vulnerabilities catalog, 27 days after it was published
2021-11-17 · Fix-by date for US federal agencies, passed 1,810 days ago

Weakness type

CWE-22

More exploited Apache vulnerabilities

CISA lists 41 exploited Apache vulnerabilities. The closest matches:

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Sources: CISA Known Exploited Vulnerabilities catalog (version 2026.10.30); EPSS data from FIRST.org; CVSS and descriptions from the NIST National Vulnerability Database. Checked 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.