Apache · HTTP Server
CVE-2021-42013
Path Traversal and Remote Code Execution in Apache HTTP Server 2.4.49 and 2.4.50 (incomplete fix of CVE-2021-41773)
What it is
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.
CISA: 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.
What to do
Apply updates per vendor instructions.
Deadline for US federal agencies: November 17, 2021
- Added to the CISA list
- November 3, 2021
- Published
- October 7, 2021
- Severity
- Critical 9.8 CVSS 3.1
- Chance of attacks in the next 30 days (EPSS)
- >99.9% in the top 0.1% of all known vulnerabilities
- Weakness
- CWE-22
- More details
- NVD · CVE.org · CISA
All references (20)
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-pathtrv-LAzg68cZ
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RMIIEFINL6FU…
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WS5RVHOIIREC…
- https://httpd.apache.org/security/vulnerabilities_24.html
- https://lists.apache.org/thread.html/r7c795cd45a3384d4d27e57618a215b0ed19cb6ca8eb070061ad5d837%40%3Cannounce.…
- https://lists.apache.org/thread.html/rb5b0e46f179f60b0c70204656bc52fcb558e961cb4d06a971e9e3efb%40%3Cusers.htt…
- http://www.openwall.com/lists/oss-security/2021/10/07/6
- http://jvn.jp/en/jp/JVN51106450/index.html
- http://www.openwall.com/lists/oss-security/2021/10/08/1
- https://lists.apache.org/thread.html/r17a4c6ce9aff662efd9459e9d1850ab4a611cb23392fc68264c72cb3%40%3Ccvs.httpd…
- http://www.openwall.com/lists/oss-security/2021/10/08/2
- http://www.openwall.com/lists/oss-security/2021/10/08/3
- http://www.openwall.com/lists/oss-security/2021/10/08/4
- http://www.openwall.com/lists/oss-security/2021/10/08/6
- http://www.openwall.com/lists/oss-security/2021/10/08/5
- http://www.openwall.com/lists/oss-security/2021/10/09/1
- http://www.openwall.com/lists/oss-security/2021/10/11/4
- http://www.openwall.com/lists/oss-security/2021/10/15/3
- http://www.openwall.com/lists/oss-security/2021/10/16/1
- https://www.oracle.com/security-alerts/cpujan2022.html
More exploited flaws from Apache
| Added | Vulnerability | Product | Severity | Attack chance |
|---|---|---|---|---|
| May 1, 2025 | Improper Escaping of Output | HTTP Server | Critical 9.1 | >99.9% |
| Nov 3, 2021 | Privilege Escalation | HTTP Server | High 7.8 | 65% |
| Nov 3, 2021 | Path Traversal | HTTP Server | High 7.5 | >99.9% |
| Oct 8, 2026 | Command Injection | Struts | High 8.1 | 97% |
| Aug 4, 2026 | Missing Encryption of Sensitive Data | Tomcat | High 7.5 | 99% |
| Apr 16, 2026 | Improper Input Validation | ActiveMQ | High 8.8 | 98% |
| Apr 1, 2025 | Path Equivalence | Tomcat | Critical 10.0 | 99.9% |
| Feb 4, 2025 | Forced Browsing | OFBiz | Critical 9.8 | >99.9% |
Sources: Known Exploited Vulnerabilities (CISA, public domain), CVE records (cve.org) and EPSS (FIRST). The chance of attacks is the EPSS estimate that someone will try to exploit the flaw in the next 30 days.