CVE-2021-40438

97

FAUCET Score

CVE-2021-40438 is a critical Server-Side Request Forgery (SSRF) vulnerability in Apache HTTP Server versions 2.4.48 and earlier, allowing a remote attacker to manipulate mod_proxy to forward requests to an arbitrary origin server. This flaw carries a CVSS score of 9.0 (CRITICAL) due to its network-based attack vector, low attack complexity, and high potential for confidentiality, integrity, and availability impact. The vulnerability is actively exploited in the wild, listed in CISA's KEV catalog, and has garnered significant community attention with numerous discussions and media coverage, despite no public Metasploit or ExploitDB modules.

Impacted Technologies

Vendor	Product	Version(s)	CPE
		8.0CPE matchmatch criteria	cpe:2.3:o:resf:rocky_linux:8.0:::::::*
		8.0CPE matchmatch criteria	cpe:2.3:o:redhat:enterprise_linux:8.0:::::::*
		8.1CPE matchmatch criteria	cpe:2.3:o:redhat:enterprise_linux_eus:8.1:::::::*
		8.2CPE matchmatch criteria	cpe:2.3:o:redhat:enterprise_linux_eus:8.2:::::::*
		8.4CPE matchmatch criteria	cpe:2.3:o:redhat:enterprise_linux_eus:8.4:::::::*

CVSS Data

CVSS version used by this source: 3.1

9.0CRITICAL

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Attack Vector

NETWORK

Attack Complexity

HIGH

Privileges Required

NONE

User Interaction

NONE

Scope

CHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

Exploitability Score

2.2

Impact Score

6.0

CvssVersion

3.1

Exploit Intelligence

EPSS Score

100.00%

Probability of exploitation in next 30 days

EPSS Percentile

100.0%

Percentile rank of EPSS score among Peer Group

As of 2026-07-27

Model: v2026.06.15

Added to KEV · Dec 1, 2021

Nuclei: CVE-2021-40438 · Oct 15, 2021

This CVE's current EPSS score of 1.0000 is in the 100th percentile among its peer group of 201 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.4 Reddit, 1.2 Bluesky, 0.8 Mastodon, and 2.3 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.8 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (35)

apachepatch availablevia llm_extracted

Fixed in: 2.4

coollabspatch availablevia llm_extracted

microsoftpatch availablevia msrc

Product: cbl2 httpd 2.4.52-1 on CBL Mariner 2.0Fixed in: 2.4.52-1

microsoftpatch availablevia msrc

Product: cm1 httpd 2.4.49-1 on CBL Mariner 1.0Fixed in: 2.4.49-1

microsoftpatch availablevia msrc

Product: 17030-16823Fixed in: 2.4.52-1

microsoftpatch availablevia msrc

Product: 16886-16820Fixed in: 2.4.49-1

oraclepatch availablevia nvd_reference

redhatpatch availablevia redhat_api

Product: JBoss Core Services for RHEL 8Fixed in: jbcs-httpd24-httpd-0:2.4.37-76.el8jbcs

redhatpatch availablevia redhat_api

Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-httpd-0:2.4.37-76.jbcs.el7

redhatpatch availablevia redhat_api

Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-mod_cluster-native-0:1.3.16-7.Final_redhat_2.jbcs.el7

redhatpatch availablevia redhat_api

Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-mod_http2-0:1.15.7-19.jbcs.el7

redhatpatch availablevia redhat_api

Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-mod_jk-0:1.2.48-18.redhat_1.jbcs.el7

redhatpatch availablevia redhat_api

Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-mod_md-1:2.0.8-38.jbcs.el7

redhatpatch availablevia redhat_api

Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-mod_security-0:2.9.2-65.GA.jbcs.el7

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 7Fixed in: httpd-0:2.4.6-97.el7_9.1

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 7.2 Advanced Update SupportFixed in: httpd-0:2.4.6-40.el7_2.7

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 7.3 Advanced Update SupportFixed in: httpd-0:2.4.6-45.el7_3.6

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 7.4 Advanced Update SupportFixed in: httpd-0:2.4.6-67.el7_4.7

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 7.6 Advanced Update Support(Disable again in 2026 - SPRHEL-7118)Fixed in: httpd-0:2.4.6-89.el7_6.2

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 7.6 Telco Extended Update SupportFixed in: httpd-0:2.4.6-89.el7_6.2

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 7.6 Update Services for SAP SolutionsFixed in: httpd-0:2.4.6-89.el7_6.2

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 7.7 Advanced Update SupportFixed in: httpd-0:2.4.6-90.el7_7.1

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 7.7 Telco Extended Update SupportFixed in: httpd-0:2.4.6-90.el7_7.1

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 7.7 Update Services for SAP SolutionsFixed in: httpd-0:2.4.6-90.el7_7.1

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 8Fixed in: httpd:2.4-8040020211008164252.522a0ee4

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 8.1 Extended Update SupportFixed in: httpd:2.4-8010020211008125020.c27ad7f8

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 8.2 Extended Update SupportFixed in: httpd:2.4-8020020211008164029.4cda2c84

redhatpatch availablevia redhat_api

Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: httpd24-httpd-0:2.4.34-22.el7.1

redhatpatch availablevia redhat_api

Product: Text-Only JBCS

redhatpatch availablevia redhat_api

Product: JBoss Core Services for RHEL 8Fixed in: jbcs-httpd24-mod_security-0:2.9.2-65.GA.el8jbcs

redhatpatch availablevia redhat_api

Product: JBoss Core Services for RHEL 8Fixed in: jbcs-httpd24-mod_md-1:2.0.8-38.el8jbcs

redhatpatch availablevia redhat_api

Product: JBoss Core Services for RHEL 8Fixed in: jbcs-httpd24-mod_jk-0:1.2.48-18.redhat_1.el8jbcs

redhatpatch availablevia redhat_api

Product: JBoss Core Services for RHEL 8Fixed in: jbcs-httpd24-mod_http2-0:1.15.7-19.el8jbcs

redhatpatch availablevia redhat_api

Product: JBoss Core Services for RHEL 8Fixed in: jbcs-httpd24-mod_cluster-native-0:1.3.16-7.Final_redhat_2.el8jbcs

power_bivendor investigatingvia llm_extracted

Vendor Advisories (7)

apachellm-apache-f398f8ed28802aa3LOW

Apache HTTP Server 2.4 vulnerabilities - The Apache HTTP Server Project

apachellm-apache-a7a91ec4c0e9421dHIGH

Apache HTTP Server 2.4 vulnerabilities - The Apache HTTP Server Project

power_billm-power_bi-1b0fc586308e0987CRITICAL

LenelS2 NetBox MOD_PROXY SSRF Vulnerability

coollabsllm-coollabs-44864ab5c7fe24c9CRITICAL

LenelS2 NetBox MOD_PROXY SSRF Vulnerability

redhatCVE-2021-40438Important

httpd: mod_proxy: SSRF via a crafted request uri-path containing "unix:"

microsoft2021-Sep/CVE-2021-40438Critical

mod_proxy SSRF

apachellm-apache-684e4d0003611bd4LOW

Apache HTTP Server 2.4 vulnerabilities - The Apache HTTP Server Project

References

cisa.gov / known-exploited-vulnerabilities-catalog

US Government Resource

cert-portal.siemens.com / productcert/pdf/ssa-685781.pdf

Third Party Advisory

httpd.apache.org / security/vulnerabilities_24.html

Release NotesVendor Advisory

lists.apache.org / thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a%40%3Cusers.httpd.apache.org%3E

Mailing List

lists.apache.org / thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37%40%3Cbugs.httpd.apache.org%3E

Mailing List

lists.apache.org / thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.httpd.apache.org%3E

Mailing List

lists.apache.org / thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c%40%3Cusers.httpd.apache.org%3E

Mailing List

lists.apache.org / thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697%40%3Cusers.httpd.apache.org%3E

Mailing List

lists.apache.org / thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029%40%3Cusers.httpd.apache.org%3E

Mailing List

lists.apache.org / thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00%40%3Cusers.httpd.apache.org%3E

Mailing List

lists.debian.org / debian-lts-announce/2021/10/msg00001.html

Mailing ListThird Party Advisory

lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/SPBR6WUYBJNACHKE65SPL7TJOHX7RHWD

Release Notes

lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/ZNCYSR3BXT36FFF4XTCPL3HDQK4VP45R

Release Notes

security.gentoo.org / glsa/202208-20

Third Party Advisory

security.netapp.com / advisory/ntap-20211008-0004

Third Party Advisory

tools.cisco.com / security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQ

Broken LinkThird Party Advisory

debian.org / security/2021/dsa-4982

Mailing ListThird Party Advisory

oracle.com / security-alerts/cpuapr2022.html

PatchThird Party Advisory

oracle.com / security-alerts/cpujan2022.html

PatchThird Party Advisory

tenable.com / security/tns-2021-17

Third Party Advisory