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)

Exp

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.

Published: 2021-10-07 Last update: 2025-10-27 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-42013 is rated Critical Active Threat (99.2/100): CVSS Critical severity, with high exploitation likelihood (EPSS 94.43%, 100th percentile). CISA KEV confirms active exploitation (added 2021-11-03) affecting Apache / HTTP Server. a weakness (CWE-22) Unauthenticated remote administrative access may be possible. The CISA remediation deadline has passed—treat as an emergency patch priority.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

CISA KEV Record for CVE-2021-42013

Name: Apache HTTP Server Path Traversal Vulnerability · CISA KEV detail

Exploit added: 2021-11-03

Action due: 2021-11-17

Required action: Apply updates per vendor instructions.

Public exploit references (Exploit-DB) for CVE-2021-42013

EDB-ID Source Kind Published Link
50512 exploit_db edb 2021-11-11 Exploit-DB ↗
50446 exploit_db edb 2021-10-25 Exploit-DB ↗
50406 exploit_db edb 2021-10-13 Exploit-DB ↗
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Exploit prediction scoring system (EPSS) score for CVE-2021-42013

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-07-17 94.46% 94.43% -0.03%
2 2025-07-16 94.43% 94.46% +0.03%
3 2025-06-16 — 94.43% —

Full EPSS history (35 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-42013

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 134c704f-9b21-4f2e-91b3-4a467353bcc0
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-42013

OS Trackers for CVE-2021-42013

vendor priority summary link
alpine — CVE-2021-42013: 1 source package rows (apache2); 9 state rows across 9 repos (3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 9, open 0. https://security.alpinelinux.org/vuln/CVE-2021-42013
debian unimportant CVE-2021-42013 unimportant priority: Debian including 1 source packages (apache2), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-42013
gentoo high CVE-2021-42013: 1 GLSA(s) (202208-20), 2 atom(s) (app-admin/apache-tools, www-servers/apache); latest impact high. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-42013
redhat high — https://access.redhat.com/security/cve/CVE-2021-42013
ubuntu high CVE-2021-42013 high priority: Ubuntu including 1 source packages (apache2), 8 status rows across 8 suites (bionic, focal, hirsute, impish, jammy, trusty, upstream, xenial): not-affected 7, needs-triage 1. https://ubuntu.com/security/CVE-2021-42013

Affected software / configurations for CVE-2021-42013

Vendor Product Version Raw CPE
apache http_server 2.4.49 cpe:2.3:a:apache:http_server:2.4.49:*:*:*:*:*:*:*
apache http_server 2.4.50 cpe:2.3:a:apache:http_server:2.4.50:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
fedoraproject fedora 35 cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
oracle instantis_enterprisetrack 17.1 cpe:2.3:a:oracle:instantis_enterprisetrack:17.1:*:*:*:*:*:*:*
oracle instantis_enterprisetrack 17.2 cpe:2.3:a:oracle:instantis_enterprisetrack:17.2:*:*:*:*:*:*:*
oracle instantis_enterprisetrack 17.3 cpe:2.3:a:oracle:instantis_enterprisetrack:17.3:*:*:*:*:*:*:*
oracle jd_edwards_enterpriseone_tools < 9.2.6.0 cpe:2.3:a:oracle:jd_edwards_enterpriseone_tools:*:*:*:*:*:*:*:*
oracle secure_backup < 18.1.0.1.0 cpe:2.3:a:oracle:secure_backup:*:*:*:*:*:*:*:*
netapp cloud_backup — cpe:2.3:a:netapp:cloud_backup:-:*:*:*:*:*:*:*

References for CVE-2021-42013

URL Tags
http://jvn.jp/en/jp/JVN51106450/index.html Third Party Advisory
http://packetstormsecurity.com/files/164501/Apache-HTTP-Server-2.4.50-Path-Traversal-Code-Execution.html Exploit Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/164609/Apache-HTTP-Server-2.4.50-Remote-Code-Execution.html Exploit Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/164629/Apache-2.4.49-2.4.50-Traversal-Remote-Code-Execution.html Exploit Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/164941/Apache-HTTP-Server-2.4.50-Remote-Code-Execution.html Exploit Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/165089/Apache-HTTP-Server-2.4.50-CVE-2021-42013-Exploitation.html Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/167397/Apache-2.4.50-Remote-Code-Execution.html Exploit Third Party Advisory VDB Entry
http://www.openwall.com/lists/oss-security/2021/10/07/6 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/10/08/1 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/10/08/2 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/10/08/3 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/10/08/4 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/10/08/5 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/10/08/6 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/10/09/1 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/10/11/4 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/10/15/3 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/10/16/1 Mailing List Third Party Advisory
https://httpd.apache.org/security/vulnerabilities_24.html Release Notes Vendor Advisory
https://lists.apache.org/thread.html/r17a4c6ce9aff662efd9459e9d1850ab4a611cb23392fc68264c72cb3%40%3Ccvs.httpd.apache.org%3E Mailing List Patch
https://lists.apache.org/thread.html/r7c795cd45a3384d4d27e57618a215b0ed19cb6ca8eb070061ad5d837%40%3Cannounce.apache.org%3E Mailing List
https://lists.apache.org/thread.html/rb5b0e46f179f60b0c70204656bc52fcb558e961cb4d06a971e9e3efb%40%3Cusers.httpd.apache.org%3E Mailing List
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RMIIEFINL6FUIOPD2A3M5XC6DH45Y3CC/ Release Notes
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WS5RVHOIIRECG65ZBTZY7IEJVWQSQPG3/ Release Notes
https://security.gentoo.org/glsa/202208-20 Third Party Advisory
https://security.netapp.com/advisory/ntap-20211029-0009/ Third Party Advisory
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-pathtrv-LAzg68cZ Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html Patch Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html Patch Third Party Advisory
https://www.povilaika.com/apache-2-4-50-exploit/ Exploit Third Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42013 US Government Resource
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