CVE-2021-44224 | Possible NULL dereference or SSRF in forward proxy configurations in Apache HTTP Server 2.4.51 and earlier

A crafted URI sent to httpd configured as a forward proxy (ProxyRequests on) can cause a crash (NULL pointer dereference) or, for configurations mixing forward and reverse proxy declarations, can allow for requests to be directed to a declared Unix Domain Socket endpoint (Server Side Request Forgery). This issue affects Apache HTTP Server 2.4.7 up to 2.4.51 (included).

Published: 2021-12-20 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-44224 is rated High Risk (72.7/100): CVSS High severity, with high exploitation likelihood (EPSS 82.30%, 100th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +73.04% over the last day, indicating growing attacker interest. High exploitation likelihood—assess exposure and prioritize remediation.

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

Exploit prediction scoring system (EPSS) score for CVE-2021-44224

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 2026-06-15 9.25% 82.30% +73.04%
2 2026-05-23 10.96% 9.25% -1.71%
3 2026-03-04 — 10.96% —

Full EPSS history (97 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-44224

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.2 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 4.2 [email protected]
6.4 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/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:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 4.9 [email protected]

Weakness enumeration for CVE-2021-44224

OS Trackers for CVE-2021-44224

vendor priority summary link
alpine high CVE-2021-44224: 1 source package rows (apache2); 8 state rows across 8 repos (3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 8, open 0. https://security.alpinelinux.org/vuln/CVE-2021-44224
debian not yet assigned CVE-2021-44224 not yet assigned 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-2021-44224
gentoo high CVE-2021-44224: 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-2021-44224
redhat medium — https://access.redhat.com/security/cve/CVE-2021-44224
suse high CVE-2021-44224 severity important: SUSE including 301 source package names (amazon/suse-sles-15-sp1-chost-byos-v20210304-hvm-ssd-x86_64, amazon/suse-sles-15-sp1-chost-byos-v20220127-hvm-ssd-x86_64, …), 503 product×package rows across 61 product lines (HPE Helion OpenStack 8, Image SLES15-SP3-EC2-HVM, … (61 product lines)): Fixed 265, Known Affected 231, Known Not Affected 7. https://www.suse.com/security/cve/CVE-2021-44224/
ubuntu medium CVE-2021-44224 medium priority: Ubuntu including 1 source packages (apache2), 8 status rows across 8 suites (bionic, focal, hirsute, impish, jammy, trusty, upstream, xenial): released 8. https://ubuntu.com/security/CVE-2021-44224

Affected software / configurations for CVE-2021-44224

Vendor Product Version Raw CPE
apache http_server >= 2.4.7, < 2.4.52 cpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
fedoraproject fedora 35 cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
fedoraproject fedora 36 cpe:2.3:o:fedoraproject:fedora:36:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
tenable tenable.sc >= 5.14.0, < 5.20.0 cpe:2.3:a:tenable:tenable.sc:*:*:*:*:*:*:*:*
tenable tenable.sc >= 5.16.0, < 202201.1 cpe:2.3:a:tenable:tenable.sc:*:*:*:*:*:*:*:*
oracle communications_element_manager < 9.0 cpe:2.3:a:oracle:communications_element_manager:*:*:*:*:*:*:*:*
oracle communications_operations_monitor 4.0 cpe:2.3:a:oracle:communications_operations_monitor:4.0:*:*:*:*:*:*:*
oracle communications_operations_monitor 4.3 cpe:2.3:a:oracle:communications_operations_monitor:4.3:*:*:*:*:*:*:*
oracle communications_operations_monitor 4.4 cpe:2.3:a:oracle:communications_operations_monitor:4.4:*:*:*:*:*:*:*
oracle communications_operations_monitor 5.0 cpe:2.3:a:oracle:communications_operations_monitor:5.0:*:*:*:*:*:*:*
oracle communications_session_report_manager < 9.0 cpe:2.3:a:oracle:communications_session_report_manager:*:*:*:*:*:*:*:*
oracle communications_session_route_manager < 9.0 cpe:2.3:a:oracle:communications_session_route_manager:*:*:*:*:*:*:*:*
oracle http_server — cpe:2.3:a:oracle:http_server:-:*:*:*:*:*:*:*
oracle http_server 12.2.1.3.0 cpe:2.3:a:oracle:http_server:12.2.1.3.0:*:*:*:*:*:*:*
oracle http_server 12.2.1.4.0 cpe:2.3:a:oracle:http_server:12.2.1.4.0:*:*:*:*:*:*:*
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:*:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:*:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2020-001:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2021-001:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2021-002:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2021-003:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2021-004:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2021-005:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2021-006:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2021-007:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2021-008:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2022-001:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2022-002:*:*:*:*:*:*
apple mac_os_x 10.15.7 cpe:2.3:o:apple:mac_os_x:10.15.7:security_update_2022-003:*:*:*:*:*:*
apple macos < 10.15.7 cpe:2.3:o:apple:macos:*:*:*:*:*:*:*:*
apple macos >= 11.0, < 11.6.6 cpe:2.3:o:apple:macos:*:*:*:*:*:*:*:*
apple macos >= 12.0.0, < 12.4 cpe:2.3:o:apple:macos:*:*:*:*:*:*:*:*

References for CVE-2021-44224

URL Tags
http://httpd.apache.org/security/vulnerabilities_24.html Vendor Advisory
http://seclists.org/fulldisclosure/2022/May/33 Mailing List Third Party Advisory
http://seclists.org/fulldisclosure/2022/May/35 Mailing List Third Party Advisory
http://seclists.org/fulldisclosure/2022/May/38 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/12/20/3 Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BFSWOH4X77CV7AH7C4RMHUBDWKQDL4YH/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RGWILBORT67SHMSLYSQZG2NMXGCMPUZO/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/X73C35MMMZGBVPQQCH7LQZUMYZNQA5FO/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Z7H26WJ6TPKNWV3QKY4BHKUKQVUTZJTD/
https://security.gentoo.org/glsa/202208-20 Third Party Advisory
https://security.netapp.com/advisory/ntap-20211224-0001/ Third Party Advisory
https://support.apple.com/kb/HT213255 Third Party Advisory
https://support.apple.com/kb/HT213256 Third Party Advisory
https://support.apple.com/kb/HT213257 Third Party Advisory
https://www.debian.org/security/2022/dsa-5035 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-2022-01 Third Party Advisory
https://www.tenable.com/security/tns-2022-03 Third Party Advisory
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