Is CVE-2021-40438 being actively exploited?

Yes. CVE-2021-40438 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added on December 1, 2021.

What is the CVSS score for CVE-2021-40438?

CVE-2021-40438 has a CVSS 3.1 base score of 9.0 (CRITICAL).

CVE-2021-40438

CRITICAL · CVSS 9.0CISA KEV: actively exploitedEPSS 100.0%EU EUVD: exploited

A crafted request uri-path can cause mod_proxy to forward the request to an origin server choosen by the remote user. This issue affects Apache HTTP Server 2.4.48 and earlier.

Key facts

CVSS score: 9.0 (v3.1)
Severity: CRITICAL
CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Weakness (CWE): CWE-918
EPSS score: 100.0% (100th percentile)
In CISA KEV: Yes, added December 1, 2021
In EU EUVD: Yes (EUVD-2021-27615)
Published: September 16, 2021
NVD last modified: August 6, 2026
Status: Analyzed

CISA Known Exploited Vulnerability

Apache HTTP Server-Side Request Forgery (SSRF)

Added to the KEV catalog on December 1, 2021; federal remediation due December 15, 2021. Known to be used in ransomware campaigns.

EU Vulnerability Database (EUVD)

This vulnerability is also tracked by ENISA as EUVD-2021-27615 in the EU Vulnerability Database. ENISA flags it as known exploited. Last updated in EUVD on August 6, 2026.

View on the EU Vulnerability Database

Affected products

apache / http server
broadcom / brocade fabric operating system firmware
debian / debian linux
debian / debian linux
debian / debian linux
f5 / f5os
fedoraproject / fedora
fedoraproject / fedora
netapp / cloud backup
netapp / clustered data ontap
netapp / storagegrid
oracle / enterprise manager ops center
oracle / http server
oracle / http server
oracle / instantis enterprisetrack
oracle / instantis enterprisetrack
oracle / instantis enterprisetrack
oracle / secure global desktop
oracle / zfs storage appliance kit
redhat / enterprise linux
redhat / enterprise linux
redhat / enterprise linux eus
redhat / enterprise linux eus
redhat / enterprise linux eus
redhat / enterprise linux eus
redhat / enterprise linux eus
redhat / enterprise linux for arm 64
redhat / enterprise linux for arm 64 eus
redhat / enterprise linux for arm 64 eus
redhat / enterprise linux for ibm z systems
redhat / enterprise linux for ibm z systems
redhat / enterprise linux for ibm z systems eus
redhat / enterprise linux for ibm z systems eus
redhat / enterprise linux for ibm z systems eus
redhat / enterprise linux for ibm z systems eus s390x
redhat / enterprise linux for power big endian
redhat / enterprise linux for power little endian
redhat / enterprise linux for power little endian
redhat / enterprise linux for power little endian eus
redhat / enterprise linux for power little endian eus
redhat / enterprise linux for power little endian eus
redhat / enterprise linux for power little endian eus
redhat / enterprise linux for power little endian eus
redhat / enterprise linux for scientific computing
redhat / enterprise linux server
redhat / enterprise linux server aus
redhat / enterprise linux server aus
redhat / enterprise linux server aus
redhat / enterprise linux server aus
redhat / enterprise linux server aus

and 34 more…

Certified products that may be affected

27 FIPS 140 or Common Criteria certified products, from automated matching by sec-certs.org.

Red Hat Enterprise Linux 8 NSS Cryptographic Module - Red Hat, Inc. - FIPS 140 5513 - active
Red Hat Enterprise Linux 8 Kernel Cryptographic API - Red Hat, LLC - FIPS 140 5461 - active
Red Hat Enterprise Linux 8 Kernel Cryptographic API - Red Hat, Inc. - FIPS 140 5089 - active
Red Hat Enterprise Linux 8.6 - Red Hat, Inc. - Common Criteria CCEVS-VR-VID-11309-2024 - archived
Red Hat Enterprise Linux 8 OpenSSL Cryptographic Module - Red Hat®, Inc. - FIPS 140 4642 - historical

See all 27 in the Security Certifications Explorer.

References

https://cert-portal.siemens.com/productcert/pdf/ssa-685781.pdf(Third Party Advisory)
https://httpd.apache.org/security/vulnerabilities_24.html(Release Notes, Vendor Advisory)
https://lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a%40%3Cusers.httpd.apache.org%3E(Mailing List)
https://lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37%40%3Cbugs.httpd.apache.org%3E(Mailing List)
https://lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.httpd.apache.org%3E(Mailing List)
https://lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c%40%3Cusers.httpd.apache.org%3E(Mailing List)
https://lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697%40%3Cusers.httpd.apache.org%3E(Mailing List)
https://lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029%40%3Cusers.httpd.apache.org%3E(Mailing List)
https://lists.apache.org/thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00%40%3Cusers.httpd.apache.org%3E(Mailing List)
https://lists.debian.org/debian-lts-announce/2021/10/msg00001.html(Mailing List, Third Party Advisory)
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR6WUYBJNACHKE65SPL7TJOHX7RHWD/(Release Notes)
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCYSR3BXT36FFF4XTCPL3HDQK4VP45R/(Release Notes)
https://security.gentoo.org/glsa/202208-20(Third Party Advisory)
https://security.netapp.com/advisory/ntap-20211008-0004/(Third Party Advisory)
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQ(Broken Link, Third Party Advisory)
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-40438(US Government Resource)
https://www.debian.org/security/2021/dsa-4982(Mailing List, 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.tenable.com/security/tns-2021-17(Third Party Advisory)

Last updated September 17, 2026 · Source: NVD, CISA KEV, FIRST.org EPSS

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