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Fencer Vulns
critical 9.8

CVE-2021-42013 kev+ ransomware in the critical feed json

Path Traversal and Remote Code Execution in Apache HTTP Server 2.4.49 and 2.4.50 (incomplete fix of CVE-2021-41773)

published 2021-10-07 5 y ago modified 2026-09-08 2 mo ago also BIT-apache-2021-42013 , EUVD-2021-29001

cvss
9.8
version 3.1, CNA
cisa kev
Exploited
added 2021-11-03, used in ransomware
epss
100.0%
EPSS 100.0% chance of exploitation in 30 days, percentile 99.9%
public exploits
5
Metasploit, Exploit-DB, plus a Nuclei check

Summary

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.

Patch / fix

cisa required action Apply updates per vendor instructions.

  • bitnami apache 2.4.50, 2.4.51
  • oracle jd_edwards_enterpriseone_tools 9.2.6.0
  • oracle secure_backup 18.1.0.1.0
  • apache2 Debian 14, Debian 13, Debian 12 2.4.51-1

debian advisories DEBIAN-CVE-2021-42013

  • apache2 openSUSE Tumbleweed 2.4.51-1.1

opensuse advisories openSUSE-SU-2024:11560-1

  • apache2 Alpine 3.24, Alpine 3.23, Alpine 3.22 +11 more 2.4.51-r0

alpine advisories ALPINE-CVE-2021-42013

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • apache Arch Linux 2.4.51-1

arch linux advisories AVG-2450

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-42013 updated cvss 8.1

httpd: path traversal and remote code execution (incomplete fix of CVE-2021-41773)

  • Red Hat Enterprise Linux 6 httpd, mod_ssl, httpd-tools, httpd-manual Red Hat Enterprise Linux 7 httpd, mod_ssl, mod_ldap, httpd-tools, mod_session, httpd-manual, +1 more Red Hat Enterprise Linux 8 httpd, mod_md, mod_ssl, mod_ldap, mod_http2, httpd-tools, +4 more Red Hat Enterprise Linux 9 httpd, mod_lua, mod_ssl, mod_ldap, httpd-core, httpd-tools, +4 more Red Hat JBoss Core Services jbcs-httpd24-httpd jbcs-httpd24-httpd Red Hat JBoss Enterprise Application Platform 6 httpd, mod_ssl, mod_ldap, httpd-tools, httpd-manual
    +1 more products
    Red Hat Software Collections httpd24-httpd, httpd24-mod_md, httpd24-mod_ssl, httpd24-mod_ldap, httpd24-httpd-tools, httpd24-mod_session, +2 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Timeline

  1. First public exploit (Metasploit auxiliary/scanner/http/apache_normalize_path)
  2. Published
  3. Added to CISA KEV
  4. CISA patch deadline
  5. CISA SSVC: exploitation active

Known exploited

Added
5 y ago
Patch by
2021-11-17 (4 y ago)
Ransomware
Known to be used in ransomware campaigns
Required action
Apply updates per vendor instructions.
Vendor, product
Apache, HTTP Server
CISA name
Apache HTTP Server Path Traversal Vulnerability

ATT&CK techniques

How it is exploited and what it leads to, in MITRE ATT&CK terms.

  • T1210 Exploitation of Remote Services exploitation
  • T1059 Command and Scripting Interpreter primary impact

kev release 2025-07-28, att&ck v16.1. KEV to ATT&CK mappings by the MITRE Center for Threat-Informed Defense (Mappings Explorer, Apache-2.0). © 2026 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation. Terms of use

CISA SSVC

Exploitation
Active, exploited in the wild
Automatable
yes
Technical impact
total
Assessed
21 mo ago

Exploit prediction

99.96% chance of exploitation in the next 30 days, higher than 99.9% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • Metasploit auxiliary/scanner/http/apache_normalize_path Apache 2.4.49/2.4.50 Traversal RCE scanner metasploit auxiliary, normal rank, 2021-05-10
  • Metasploit exploit/multi/http/apache_normalize_path_rce Apache 2.4.49/2.4.50 Traversal RCE metasploit exploit, excellent rank, 2021-05-10
  • EDB-50512 Apache HTTP Server 2.4.50 - Remote Code Execution (RCE) (3) webapps, 2021-11-11
  • EDB-50446 Apache HTTP Server 2.4.50 - Remote Code Execution (RCE) (2) webapps, 2021-10-25
  • EDB-50406 Apache HTTP Server 2.4.50 - Path Traversal & Remote Code Execution (RCE) webapps, 2021-10-13
  • Nuclei template Apache 2.4.49/2.4.50 - Path Traversal and Remote Code Execution nuclei detection template
  • packetstormsecurity.com http://packetstormsecurity.com/files/164629/Apache-2.4.49-2.4.50-Traversal-Remote-Code-Execution.html referenced PoC, tagged "exploit" by a source, unverified
  • packetstormsecurity.com http://packetstormsecurity.com/files/164941/Apache-HTTP-Server-2.4.50-Remote-Code-Execution.html referenced PoC, tagged "exploit" by a source, unverified
  • packetstormsecurity.com http://packetstormsecurity.com/files/164501/Apache-HTTP-Server-2.4.50-Path-Traversal-Code-Execution.html referenced PoC, tagged "exploit" by a source, unverified
  • packetstormsecurity.com http://packetstormsecurity.com/files/164609/Apache-HTTP-Server-2.4.50-Remote-Code-Execution.html referenced PoC, tagged "exploit" by a source, unverified
  • packetstormsecurity.com http://packetstormsecurity.com/files/167397/Apache-2.4.50-Remote-Code-Execution.html referenced PoC, tagged "exploit" by a source, unverified
  • povilaika.com https://www.povilaika.com/apache-2-4-50-exploit/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CISA ADP 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P
OSV 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
bitnami apache
>=2.4.49, <2.4.50
>=2.4.50, <2.4.51
2.4.50
2.4.51

Affected products

  • Apache Software Foundation Apache HTTP Server

Classification

Weakness
  • CWE-22 Improper Limitation of a Pathname to a Restricted Directory
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.