CVE-2021-44224: Possible NULL dereference or SSRF in forward proxy configurations in Apache HTTP Server 2.4.51 and earlier
Noroxi assessment
Priority: Plan (action score 57/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 82.2% (FIRST EPSS); higher than 99.6% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
- Fixed version: httpd (AlmaLinux:8) 2.4.37-47.module_el8.6.0+2935+fb177b09.2, 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma; httpd-devel (AlmaLinux:8) 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma, 2.4.37-47.module_el8.6.0+2935+fb177b09.2; httpd-filesystem (AlmaLinux:8) 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma, 2.4.37-47.module_el8.6.0+2935+fb177b09.2.
- Mentioned 3 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Add it to your regular patch cycle. Upgrade to httpd (AlmaLinux:8) 2.4.37-47.module_el8.6.0+2935+fb177b09.2, 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma; httpd-devel (AlmaLinux:8) 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma, 2.4.37-47.module_el8.6.0+2935+fb177b09.2; httpd-filesystem (AlmaLinux:8) 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma, 2.4.37-47.module_el8.6.0+2935+fb177b09.2 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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
- Dec 20, 2021
- Updated
- Jun 17, 2026
- EPSS
- 82.2% · 99th percentile
- CWE
- CWE-476
Report tools
Action score
57
Add it to your regular patch cycle.
- CVSS
- 32 / 40 · 8.2 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 25 / 30 · 82.2%
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
Is Apache HTTP Server on your server exposed to the internet?Run a port scan
Is your version affected? Check itNoroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| apache | http server | cpe:2.3:a:apache:http_server |
| fedoraproject | fedora | cpe:2.3:o:fedoraproject:fedora |
| debian | debian linux | cpe:2.3:o:debian:debian_linux |
| tenable | tenable.sc | cpe:2.3:a:tenable:tenable.sc |
| oracle | communications element manager | cpe:2.3:a:oracle:communications_element_manager |
| oracle | communications operations monitor | cpe:2.3:a:oracle:communications_operations_monitor |
| oracle | communications session report manager | cpe:2.3:a:oracle:communications_session_report_manager |
| oracle | communications session route manager | cpe:2.3:a:oracle:communications_session_route_manager |
| oracle | http server | cpe:2.3:a:oracle:http_server |
| oracle | instantis enterprisetrack | cpe:2.3:a:oracle:instantis_enterprisetrack |
| apple | mac os x | cpe:2.3:o:apple:mac_os_x |
| apple | macos | cpe:2.3:o:apple:macos |
Using http server? Add it to your stack and be the first to know about CVEs like this one. (Apache HTTP)
Is Apache HTTP Server on your server exposed to the internet?
The free port scanner finds the open ports on your server and matches the service versions it can read against known vulnerabilities. No account needed.
Run a port scanVersions reported by the vendor
Affected version ranges reported by the assigning authority (apache). Independent of NVD's CPE analysis and usually ahead of it.
Apache Software Foundation Apache HTTP Server
- 2.4.7 and later · before Apache HTTP Server 2.4*affected
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- apache http server2.4.7 and later · before 2.4.52
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| AlmaLinux:8 | httpd | before 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 |
| AlmaLinux:8 | httpd | before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma |
| AlmaLinux:8 | httpd-devel | before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma |
| AlmaLinux:8 | httpd-devel | before 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 |
| AlmaLinux:8 | httpd-filesystem | before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma |
| AlmaLinux:8 | httpd-filesystem | before 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 |
| AlmaLinux:8 | httpd-manual | before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma |
| AlmaLinux:8 | httpd-manual | before 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 |
| AlmaLinux:8 | httpd-tools | before 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 |
| AlmaLinux:8 | httpd-tools | before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma |
| AlmaLinux:8 | mod_http2 | before 1.15.7-5.module_el8.6.0+2872+fe0ff7aa | 1.15.7-5.module_el8.6.0+2872+fe0ff7aa |
| AlmaLinux:8 | mod_ldap | before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma |
| AlmaLinux:8 | mod_ldap | before 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 |
| AlmaLinux:8 | mod_md | before 1:2.0.8-8.module_el8.6.0+2872+fe0ff7aa | 1:2.0.8-8.module_el8.6.0+2872+fe0ff7aa |
| AlmaLinux:8 | mod_proxy_html | before 1:2.4.37-47.module_el8.6.0+2935+fb177b09.2 | 1:2.4.37-47.module_el8.6.0+2935+fb177b09.2 |
| AlmaLinux:8 | mod_proxy_html | before 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma |
| AlmaLinux:8 | mod_session | before 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 |
| AlmaLinux:8 | mod_session | before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma |
| AlmaLinux:8 | mod_ssl | before 1:2.4.37-47.module_el8.6.0+2935+fb177b09.2 | 1:2.4.37-47.module_el8.6.0+2935+fb177b09.2 |
| AlmaLinux:8 | mod_ssl | before 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma |
| Alpine:v3.12 | apache2 | before 2.4.52-r0 | 2.4.52-r0 |
| Debian:10 | apache2 | before 2.4.38-3+deb10u7 | 2.4.38-3+deb10u7 |
| Debian:11 | apache2 | before 2.4.52-1~deb11u2 | 2.4.52-1~deb11u2 |
| Debian:12 | apache2 | before 2.4.52-1 | 2.4.52-1 |
+70
Same product
apache: all recordsOther highest-scoring records for the same primary product.
- CVE-2021-42013Path Traversal and Remote Code Execution in Apache HTTP Server 2.4.49 and 2.4.50 (incomplete fix of CVE-2021-41773)KEV99Now
- CVE-2021-41773Path traversal and file disclosure vulnerability in Apache HTTP Server 2.4.49KEV99Now
- CVE-2024-38475Apache HTTP Server weakness in mod_rewrite when first segment of substitution matches filesystem path.KEV96Now
Published before and after this one in the same product
- ← EarlierCVE-2021-39275Sep 16, 2021 · ap_escape_quotes buffer overflow51Plan
- ← EarlierCVE-2021-41524Oct 5, 2021 · null pointer dereference in h2 fuzzing38Monitor
- Later →CVE-2021-44790Dec 20, 2021 · Possible buffer overflow when parsing multipart content in mod_lua of Apache HTTP Server 2.4.51 and earlier68This week
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| almalinux:httpd | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:httpd-devel | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:httpd-filesystem | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:httpd-manual | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:httpd-tools | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_http2 | 1.15.7-5.module_el8.6.0+2872+fe0ff7aa · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_ldap | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_md | 1:2.0.8-8.module_el8.6.0+2872+fe0ff7aa · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_proxy_html | 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_session | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_ssl | 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma · AlmaLinux:8 | Package registry (OSV) |
| alpine:apache2 | 2.4.52-r0 · Alpine:v3.12 | Package registry (OSV) |
| debian:apache2 | 2.4.52-1 · Debian:12 | Package registry (OSV) |
| opensuse:apache2 | 2.4.51-3.37.1 · openSUSE:Leap 15.3 | Package registry (OSV) |
| opensuse:chromium | 99.0.4844.84-bp153.2.75.1 · openSUSE:Leap 15.3 | Package registry (OSV) |
| red hat:httpd | 0:2.4.37-47.module+el8.6.0+14529+083145da.1 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:httpd-debuginfo | 0:2.4.37-47.module+el8.6.0+14529+083145da.1 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:httpd-debugsource | 0:2.4.37-47.module+el8.6.0+14529+083145da.1 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:httpd-devel | 0:2.4.37-47.module+el8.6.0+14529+083145da.1 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:httpd-filesystem | 0:2.4.37-47.module+el8.6.0+14529+083145da.1 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:httpd-manual | 0:2.4.37-47.module+el8.6.0+14529+083145da.1 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:httpd-tools | 0:2.4.37-47.module+el8.6.0+14529+083145da.1 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:httpd-tools-debuginfo | 0:2.4.37-47.module+el8.6.0+14529+083145da.1 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:mod_http2 | 0:1.15.7-5.module+el8.6.0+13996+01710940 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:mod_http2-debuginfo | 0:1.15.7-5.module+el8.6.0+13996+01710940 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:mod_http2-debugsource | 0:1.15.7-5.module+el8.6.0+13996+01710940 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| red hat:mod_ldap | 0:2.4.37-47.module+el8.6.0+14529+083145da.1 · Red Hat:enterprise_linux:8::appstream | Package registry (OSV) |
| rocky linux:httpd | 0:2.4.37-47.module+el8.6.0+823+f143cee1.1 · Rocky Linux:8 | Package registry (OSV) |
| rocky linux:mod_http2 | 0:1.15.7-5.module+el8.6.0+823+f143cee1 · Rocky Linux:8 | Package registry (OSV) |
| rocky linux:mod_md | 1:2.0.8-8.module+el8.5.0+695+1fa8055e · Rocky Linux:8 | Package registry (OSV) |
+2
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
Bug bounty scope
The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.
National notice (Türkiye Cybersecurity Directorate / USOM)
Official security notices citing this record; remediation advice is on the agency's page.
- TR-22-0362 · May 17, 2022(Apple Güvenlik Güncellemesi)
- TR-22-0039 · Jan 13, 2022(IBM Güvenlik Bülteni)
- TR-21-1017 · Dec 23, 2021(Apache HTTP Server Güvenlik Bildirimi)
Not on record for this CVE: EPSS history · patch commit or PR link · variant or chain candidate.
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- none
- Integrity
- low · data or configuration can be modified
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- Low
- Availability impact
- High
Weakness class (CWE)
CWE-476 · NULL Pointer DereferenceCVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log (1)
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (18 more)Show less
- seclists.org/fulldisclosure/2022/May/33
- seclists.org/fulldisclosure/2022/May/35
- seclists.org/fulldisclosure/2022/May/38
- www.openwall.com/lists/oss-security/2021/12/20/3
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BFSWOH4X77CV7AH7C4RMHUBDWKQDL4YH/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RGWILBORT67SHMSLYSQZG2NMXGCMPUZO/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/X73C35MMMZGBVPQQCH7LQZUMYZNQA5FO/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Z7H26WJ6TPKNWV3QKY4BHKUKQVUTZJTD/
- security.gentoo.org/glsa/202208-20
- security.netapp.com/advisory/ntap-20211224-0001/
- support.apple.com/kb/HT213255
- support.apple.com/kb/HT213256
- support.apple.com/kb/HT213257
- www.debian.org/security/2022/dsa-5035
- www.oracle.com/security-alerts/cpuapr2022.html
- www.oracle.com/security-alerts/cpujan2022.html
- www.tenable.com/security/tns-2022-01
- www.tenable.com/security/tns-2022-03
Vendor advisories and official records. Exploit/PoC links are deliberately left out.