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Fencer Vulns
critical 9.0

CVE-2021-40438 kev+ ransomware in the critical feed json

mod_proxy SSRF

published 2021-09-16 5 y ago modified 2026-10-16 24 d ago also BIT-apache-2021-40438 , EUVD-2021-27615

cvss
9.0
version 3.1, CNA
cisa kev
Exploited
added 2021-12-01, used in ransomware
epss
100.0%
EPSS 100.0% chance of exploitation in 30 days, percentile 99.9%
public exploits
0
none known, plus a Nuclei check

Summary

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.

Patch / fix

cisa required action Apply updates per vendor instructions.

  • bitnami apache 2.4.49
  • siemens sinec_nms 1.0.3
  • siemens sinema_remote_connect_server 3.1
  • apache2 Debian 14, Debian 13, Debian 12 2.4.49-1

debian advisories DEBIAN-CVE-2021-40438

  • apache2 Ubuntu 18.04 LTS 2.4.29-1ubuntu4.18
  • apache2 Ubuntu 20.04 LTS 2.4.41-4ubuntu3.6
  • apache2 Ubuntu Pro 16.04 LTS 2.4.18-2ubuntu3.17+esm3

ubuntu advisories UBUNTU-CVE-2021-40438

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • httpd RHEL 8 2.4.37-39.module+el8.4.0+12865+a7065a39.1
  • mod_md RHEL 8 1:2.0.8-8.module+el8.3.0+6814+67d1e611
  • mod_ssl RHEL 8 1:2.4.37-39.module+el8.4.0+12865+a7065a39.1
  • mod_ldap RHEL 8 2.4.37-39.module+el8.4.0+12865+a7065a39.1
  • mod_http2 RHEL 8 1.15.7-3.module+el8.4.0+8625+d397f3da
  • httpd-tools RHEL 8 2.4.37-39.module+el8.4.0+12865+a7065a39.1
  • mod_session RHEL 8 2.4.37-39.module+el8.4.0+12865+a7065a39.1
  • httpd-manual RHEL 8 2.4.37-39.module+el8.4.0+12865+a7065a39.1

red hat advisories RHSA-2021:3816RHSA-2021:3754RHSA-2021:3746RHSA-2021:3856RHSA-2021:3837RHSA-2021:3836

  • apache2 SLE Module for Server Applications 15 SP3, SLE Module for Server Applications 15 SP2, SLE Module for Package Hub 15 SP3 +2 more 2.4.43-3.32.1
  • apache2 SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +7 more 2.4.33-3.55.1
  • apache2 SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +11 more 2.4.23-29.80.1

suse advisories SUSE-SU-2021:3522-1SUSE-SU-2021:3335-1SUSE-SU-2021:3299-1

  • owasp-modsecurity-crs openSUSE Tumbleweed 4.9.0-1.1
  • apache2 openSUSE Leap 15.2 2.4.43-lp152.2.21.1
  • apache2 openSUSE Leap 15.3 2.4.43-3.32.1

opensuse advisories openSUSE-SU-2025:14708-1openSUSE-SU-2021:1438-1openSUSE-SU-2021:3522-1

  • mod_md AlmaLinux 8 1:2.0.8-8.module_el8.5.0+2609+b30d9eec
  • mod_md AlmaLinux 8 1:2.0.8-8.module_el8.6.0+2872+fe0ff7aa
  • mod_http2 AlmaLinux 8 1.15.7-3.module_el8.5.0+2609+b30d9eec
  • httpd AlmaLinux 8 2.4.37-43.module_el8.5.0+2597+c4b14997.alma
  • mod_ssl AlmaLinux 8 1:2.4.37-43.module_el8.5.0+2597+c4b14997.alma
  • mod_ldap AlmaLinux 8 2.4.37-43.module_el8.5.0+2597+c4b14997.alma
  • httpd-tools AlmaLinux 8 2.4.37-43.module_el8.5.0+2597+c4b14997.alma
  • mod_session AlmaLinux 8 2.4.37-43.module_el8.5.0+2597+c4b14997.alma

almalinux advisories ALBA-2021:4604ALSA-2021:4537ALSA-2021:3816

  • httpd Rocky Linux 8 2.4.37-39.module+el8.4.0+571+fd70afb1
  • mod_md Rocky Linux 8 1:2.0.8-8.module+el8.5.0+695+1fa8055e
  • mod_md Rocky Linux 8 1:2.0.8-8.module+el8.4.0+553+7a69454b
  • mod_http2 Rocky Linux 8 1.15.7-3.module+el8.4.0+553+7a69454b
  • mod_http2 Rocky Linux 8 1.15.7-3.module+el8.5.0+695+1fa8055e

rocky linux advisories RLSA-2021:3816

  • apache2 Alpine 3.24, Alpine 3.23, Alpine 3.22 +11 more 2.4.49-r0

alpine advisories ALPINE-CVE-2021-40438

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

  • httpd CBL-Mariner 2.0 2.4.52-1

azure linux advisories AZL-6487

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

  • apache Arch Linux 2.4.49-1

arch linux advisories AVG-2289

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-2021-40438 updated cvss 9.0

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

  • Red Hat Enterprise Linux AppStream (v. 8) mod_md 2.0.8-8.module+el8.3.0+6814+67d1e611, httpd 2.4.37-39.module+el8.4.0+12865+a7065a39.1, mod_http2 1.15.7-3.module+el8.4.0+8625+d397f3da, mod_ssl 2.4.37-39.module+el8.4.0+12865+a7065a39.1, mod_ldap 2.4.37-39.module+el8.4.0+12865+a7065a39.1, httpd-tools 2.4.37-39.module+el8.4.0+12865+a7065a39.1, +4 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2021:3816
  • Red Hat Enterprise Linux AppStream EUS (v. 8.1) httpd 2.4.37-16.module+el8.1.0+12900+7e6e5641.1, mod_md 2.4.37-16.module+el8.1.0+12900+7e6e5641.1, mod_http2 1.11.3-3.module+el8.1.0+7763+babdfe5b.1, mod_ssl 2.4.37-16.module+el8.1.0+12900+7e6e5641.1, mod_ldap 2.4.37-16.module+el8.1.0+12900+7e6e5641.1, httpd-tools 2.4.37-16.module+el8.1.0+12900+7e6e5641.1, +4 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2021:3837
  • Red Hat Enterprise Linux AppStream EUS (v. 8.2) mod_md 2.0.8-7.module+el8.2.0+5531+7e4d69a2, httpd 2.4.37-21.module+el8.2.0+12904+53ee7aba.1, mod_http2 1.11.3-3.module+el8.2.0+7758+84b4ca3e.1, mod_ssl 2.4.37-21.module+el8.2.0+12904+53ee7aba.1, mod_ldap 2.4.37-21.module+el8.2.0+12904+53ee7aba.1, httpd-tools 2.4.37-21.module+el8.2.0+12904+53ee7aba.1, +4 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2021:3836
  • Red Hat Enterprise Linux Client Optional (v. 7) httpd 2.4.6-97.el7_9.1, mod_ssl 2.4.6-97.el7_9.1, mod_ldap 2.4.6-97.el7_9.1, httpd-tools 2.4.6-97.el7_9.1, mod_session 2.4.6-97.el7_9.1, httpd-manual 2.4.6-97.el7_9.1, +1 more Red Hat Enterprise Linux ComputeNode Optional (v. 7) httpd 2.4.6-97.el7_9.1, mod_ssl 2.4.6-97.el7_9.1, mod_ldap 2.4.6-97.el7_9.1, httpd-tools 2.4.6-97.el7_9.1, mod_session 2.4.6-97.el7_9.1, httpd-manual 2.4.6-97.el7_9.1, +1 more Red Hat Enterprise Linux Server (v. 7) httpd 2.4.6-97.el7_9.1, mod_ssl 2.4.6-97.el7_9.1, httpd-tools 2.4.6-97.el7_9.1, mod_session 2.4.6-97.el7_9.1, httpd-manual 2.4.6-97.el7_9.1 Red Hat Enterprise Linux Server AUS (v. 7.2) httpd 2.4.6-40.el7_2.7, mod_ssl 2.4.6-40.el7_2.7, httpd-tools 2.4.6-40.el7_2.7, httpd-manual 2.4.6-40.el7_2.7 Red Hat Enterprise Linux Server AUS (v. 7.3) httpd 2.4.6-45.el7_3.6, mod_ssl 2.4.6-45.el7_3.6, httpd-tools 2.4.6-45.el7_3.6, httpd-manual 2.4.6-45.el7_3.6 Red Hat Enterprise Linux Server AUS (v. 7.4) httpd 2.4.6-67.el7_4.7, mod_ssl 2.4.6-67.el7_4.7, httpd-tools 2.4.6-67.el7_4.7, mod_session 2.4.6-67.el7_4.7, httpd-manual 2.4.6-67.el7_4.7
    +18 more products
    Red Hat Enterprise Linux Server AUS (v. 7.6) httpd 2.4.6-89.el7_6.2, mod_ssl 2.4.6-89.el7_6.2, httpd-tools 2.4.6-89.el7_6.2, mod_session 2.4.6-89.el7_6.2, httpd-manual 2.4.6-89.el7_6.2 Red Hat Enterprise Linux Server AUS (v. 7.7) httpd 2.4.6-90.el7_7.1, mod_ssl 2.4.6-90.el7_7.1, httpd-tools 2.4.6-90.el7_7.1, mod_session 2.4.6-90.el7_7.1, httpd-manual 2.4.6-90.el7_7.1 Red Hat Enterprise Linux Server E4S (v. 7.6) httpd 2.4.6-89.el7_6.2, mod_ssl 2.4.6-89.el7_6.2, httpd-tools 2.4.6-89.el7_6.2, mod_session 2.4.6-89.el7_6.2, httpd-manual 2.4.6-89.el7_6.2 Red Hat Enterprise Linux Server E4S (v. 7.7) httpd 2.4.6-90.el7_7.1, mod_ssl 2.4.6-90.el7_7.1, httpd-tools 2.4.6-90.el7_7.1, mod_session 2.4.6-90.el7_7.1, httpd-manual 2.4.6-90.el7_7.1 Red Hat Enterprise Linux Server Optional (v. 7) mod_ldap 2.4.6-97.el7_9.1, mod_proxy_html 2.4.6-97.el7_9.1 Red Hat Enterprise Linux Server Optional AUS (v. 7.2) mod_ldap 2.4.6-40.el7_2.7, mod_session 2.4.6-40.el7_2.7, mod_proxy_html 2.4.6-40.el7_2.7 Red Hat Enterprise Linux Server Optional AUS (v. 7.3) mod_ldap 2.4.6-45.el7_3.6, mod_session 2.4.6-45.el7_3.6, mod_proxy_html 2.4.6-45.el7_3.6 Red Hat Enterprise Linux Server Optional AUS (v. 7.4) mod_ldap 2.4.6-67.el7_4.7, mod_proxy_html 2.4.6-67.el7_4.7 Red Hat Enterprise Linux Server Optional AUS (v. 7.6) mod_ldap 2.4.6-89.el7_6.2, mod_proxy_html 2.4.6-89.el7_6.2 Red Hat Enterprise Linux Server Optional AUS (v. 7.7) mod_ldap 2.4.6-90.el7_7.1, mod_proxy_html 2.4.6-90.el7_7.1 Red Hat Enterprise Linux Server Optional E4S (v. 7.6) mod_ldap 2.4.6-89.el7_6.2, mod_proxy_html 2.4.6-89.el7_6.2 Red Hat Enterprise Linux Server Optional E4S (v. 7.7) mod_ldap 2.4.6-90.el7_7.1, mod_proxy_html 2.4.6-90.el7_7.1 Red Hat Enterprise Linux Server Optional TUS (v. 7.6) mod_ldap 2.4.6-89.el7_6.2, mod_proxy_html 2.4.6-89.el7_6.2 Red Hat Enterprise Linux Server Optional TUS (v. 7.7) mod_ldap 2.4.6-90.el7_7.1, mod_proxy_html 2.4.6-90.el7_7.1 Red Hat Enterprise Linux Server TUS (v. 7.6) httpd 2.4.6-89.el7_6.2, mod_ssl 2.4.6-89.el7_6.2, httpd-tools 2.4.6-89.el7_6.2, mod_session 2.4.6-89.el7_6.2, httpd-manual 2.4.6-89.el7_6.2 Red Hat Enterprise Linux Server TUS (v. 7.7) httpd 2.4.6-90.el7_7.1, mod_ssl 2.4.6-90.el7_7.1, httpd-tools 2.4.6-90.el7_7.1, mod_session 2.4.6-90.el7_7.1, httpd-manual 2.4.6-90.el7_7.1 Red Hat Enterprise Linux Workstation (v. 7) httpd 2.4.6-97.el7_9.1, mod_ssl 2.4.6-97.el7_9.1, httpd-tools 2.4.6-97.el7_9.1, mod_session 2.4.6-97.el7_9.1, httpd-manual 2.4.6-97.el7_9.1 Red Hat Enterprise Linux Workstation Optional (v. 7) mod_ldap 2.4.6-97.el7_9.1, mod_proxy_html 2.4.6-97.el7_9.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2021:3856
  • Red Hat JBoss Core Services
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2021:3745
  • Red Hat JBoss Core Services on RHEL 7 Server jbcs-httpd24-httpd 2.4.37-76.jbcs.el7, jbcs-httpd24-mod_md 2.0.8-38.jbcs.el7, jbcs-httpd24-mod_ssl 2.4.37-76.jbcs.el7, jbcs-httpd24-mod_ldap 2.4.37-76.jbcs.el7, jbcs-httpd24-mod_http2 1.15.7-19.jbcs.el7, jbcs-httpd24-httpd-tools 2.4.37-76.jbcs.el7, +9 more Red Hat JBoss Core Services on RHEL 8 jbcs-httpd24-httpd 2.4.37-76.el8jbcs, jbcs-httpd24-mod_md 2.0.8-38.el8jbcs, jbcs-httpd24-mod_ssl 2.4.37-76.el8jbcs, jbcs-httpd24-mod_ldap 2.4.37-76.el8jbcs, jbcs-httpd24-mod_http2 1.15.7-19.el8jbcs, jbcs-httpd24-httpd-tools 2.4.37-76.el8jbcs, +9 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2021:3746
  • Red Hat Software Collections for Red Hat Enterprise Linux Server (v. 7) httpd24-httpd 2.4.34-22.el7.1, httpd24-mod_ssl 2.4.34-22.el7.1, httpd24-mod_ldap 2.4.34-22.el7.1, httpd24-httpd-tools 2.4.34-22.el7.1, httpd24-mod_session 2.4.34-22.el7.1, httpd24-httpd-manual 2.4.34-22.el7.1, +1 more Red Hat Software Collections for Red Hat Enterprise Linux Workstation (v. 7) httpd24-httpd 2.4.34-22.el7.1, httpd24-mod_ssl 2.4.34-22.el7.1, httpd24-mod_ldap 2.4.34-22.el7.1, httpd24-httpd-tools 2.4.34-22.el7.1, httpd24-mod_session 2.4.34-22.el7.1, httpd24-httpd-manual 2.4.34-22.el7.1, +1 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2021:3754
  • Red Hat Enterprise Linux 6 httpd, mod_ssl, httpd-tools, httpd-manual Red Hat Enterprise Linux 9 httpd, mod_lua, mod_ssl, mod_ldap, httpd-core, httpd-tools, +4 more Red Hat JBoss Enterprise Application Platform 6 httpd, mod_ssl, mod_ldap, httpd-tools, httpd-manual
    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

cisa ICSA-22-167-06 updated cvss 9.0

Siemens Apache HTTP Server

  • Siemens SINEC NMS <V1.0.3
    affected: fixed in V1.0.3, mitigation support.industry.siemens.com
  • Siemens SINEMA Server V14
    affected: mitigation, no fix planned

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Timeline

  1. Published
  2. CISA SSVC: exploitation active
  3. Added to CISA KEV
  4. CISA patch deadline

Known exploited

Added
4 y ago
Patch by
2021-12-15 (4 y ago)
Ransomware
Known to be used in ransomware campaigns
Required action
Apply updates per vendor instructions.
Vendor, product
Apache, Apache
CISA name
Apache HTTP Server-Side Request Forgery (SSRF)

CISA SSVC

Exploitation
Active, exploited in the wild
Automatable
yes
Technical impact
total
Assessed
5 y ago

Exploit prediction

100.00% chance of exploitation in the next 30 days, higher than 99.9% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • Nuclei template Apache <= 2.4.48 Mod_Proxy - Server-Side Request Forgery nuclei detection template

CVSS scores

assigned by version score vector
CISA ADP 3.1 9.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
NVD 3.1 9.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
CNA 3.1 9.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
NVD 2.0 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P
OSV 3.1 9.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
bitnami apache
<2.4.49
2.4.49

Affected products

  • Apache Software Foundation Apache HTTP Server

Classification

Weakness
  • CWE-918 Server-Side Request Forgery
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.