CRITICAL CISA KEV

CVE-2021-40438

CVSS v3

CRITICAL

EPSS Score

100.0 %

exploit probability, as of 2026-10-19

CISA KEV

Yes

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

apacheBitnamiall versions · fixed in 2.4.49
httpdAlmaLinux:8all versions · fixed in 2.4.37-43.module_el8.5.0+2597+c4b14997.almaand 6 other packages
mod_http2AlmaLinux:8all versions · fixed in 1.15.7-3.module_el8.5.0+2609+b30d9eec
mod_mdAlmaLinux:8all versions · fixed in 1:2.0.8-8.module_el8.6.0+2872+fe0ff7aa
mod_sslAlmaLinux:8all versions · fixed in 1:2.4.37-43.module_el8.5.0+2597+c4b14997.almaand 1 other package

Vendor advisories

CVE-2021-40438 Red Hat Product Security532 products fixed
httpd: mod_proxy: SSRF via a crafted request uri-path containing "unix:"
ICSA-22-167-06 CISA2 known affected
Siemens Apache HTTP Server
SINEC NMS · SINEMA Server V14
SSA-685781 Siemens ProductCERT2 known affected
SSA-685781: Multiple Vulnerabilities in Apache HTTP Server Affecting Siemens Products
SINEC NMS · SINEMA Server V14
RHSA-2021:3856 Red Hat Product Security186 products fixed
Red Hat Security Advisory: httpd security update
RHSA-2021:3836 Red Hat Product Security85 products fixed
Red Hat Security Advisory: httpd:2.4 security update
RHSA-2021:3837 Red Hat Product Security80 products fixed
Red Hat Security Advisory: httpd:2.4 security update

4 more advisories

Full record on NVD

Description

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.

CISA Known Exploited Vulnerability

Date Added: 2021-12-01
Patch Due Date: 2021-12-15
Ransomware Use: Unknown

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Published: 2021-09-16
Last Modified: 2026-08-05

Frequently asked questions

What is CVE-2021-40438?

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.

Is CVE-2021-40438 actively exploited?

Yes. CVE-2021-40438 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, meaning it has been confirmed as actively exploited in the wild. CISA requires federal agencies to patch by 2021-12-15.

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

CVE-2021-40438 has a CVSS v3 base score of 9 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H.

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