Vulnerability · Published Aug 16, 2021 · Assigned by apache
CVE-2021-33193Request splitting via HTTP/2 method injection and mod_proxy
High 7.5
In plain English
A high-severity security flaw in Apache HTTP Server from Apache Software Foundation. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 46.2% (higher than 99% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS NVD)7.5High
Exploit odds (30 days)46.2%top 1.2% of all CVEs
Exploited in the wildNo reportsnot in CISA KEV
Attack toolingNoneno public tooling known
Official description
A crafted method sent through HTTP/2 will bypass validation and be forwarded by mod_proxy, which can lead to request splitting or cache poisoning. This issue affects Apache HTTP Server 2.4.17 to 2.4.48.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:8 | httpd | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | ALSA-2022:1915 |
| AlmaLinux:8 | httpd | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | ALSA-2022:1915 |
| AlmaLinux:8 | httpd-devel | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | ALSA-2022:1915 |
| AlmaLinux:8 | httpd-devel | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | ALSA-2022:1915 |
| AlmaLinux:8 | httpd-filesystem | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | ALSA-2022:1915 |
| AlmaLinux:8 | httpd-filesystem | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | ALSA-2022:1915 |
| AlmaLinux:8 | httpd-manual | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | ALSA-2022:1915 |
| AlmaLinux:8 | httpd-manual | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | ALSA-2022:1915 |
| AlmaLinux:8 | httpd-tools | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | ALSA-2022:1915 |
| AlmaLinux:8 | httpd-tools | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | ALSA-2022:1915 |
| AlmaLinux:8 | mod_http2 | 1.15.7-5.module_el8.6.0+2872+fe0ff7aa | ALSA-2022:1915 |
| AlmaLinux:8 | mod_ldap | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | ALSA-2022:1915 |
| AlmaLinux:8 | mod_ldap | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | ALSA-2022:1915 |
| AlmaLinux:8 | mod_md | 1:2.0.8-8.module_el8.6.0+2872+fe0ff7aa | ALSA-2022:1915 |
| AlmaLinux:8 | mod_proxy_html | 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | ALSA-2022:1915 |
| AlmaLinux:8 | mod_proxy_html | 1:2.4.37-47.module_el8.6.0+2935+fb177b09.2 | ALSA-2022:1915 |
| AlmaLinux:8 | mod_session | 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | ALSA-2022:1915 |
| AlmaLinux:8 | mod_session | 2.4.37-47.module_el8.6.0+2935+fb177b09.2 | ALSA-2022:1915 |
| AlmaLinux:8 | mod_ssl | 1:2.4.37-47.module_el8.6.0+2935+fb177b09.2 | ALSA-2022:1915 |
| AlmaLinux:8 | mod_ssl | 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma | ALSA-2022:1915 |
| Alpine:v3.20 | apache2 | 2.4.49-r0 | ALPINE-CVE-2021-33193 |
| Alpine:v3.21 | apache2 | 2.4.49-r0 | ALPINE-CVE-2021-33193 |
| Alpine:v3.22 | apache2 | 2.4.49-r0 | ALPINE-CVE-2021-33193 |
| Alpine:v3.23 | apache2 | 2.4.49-r0 | ALPINE-CVE-2021-33193 |
| Alpine:v3.24 | apache2 | 2.4.49-r0 | ALPINE-CVE-2021-33193 |
| Debian:12 | apache2 | 2.4.48-4 | DEBIAN-CVE-2021-33193 |
| Debian:13 | apache2 | 2.4.48-4 | DEBIAN-CVE-2021-33193 |
| Debian:14 | apache2 | 2.4.48-4 | DEBIAN-CVE-2021-33193 |
| Rocky Linux:8 | httpd | 0:2.4.37-47.module+el8.6.0+823+f143cee1.1 | RLSA-2022:1915 |
| Rocky Linux:8 | mod_http2 | 0:1.15.7-5.module+el8.6.0+823+f143cee1 | RLSA-2022:1915 |
| Rocky Linux:8 | mod_md | 1:2.0.8-8.module+el8.4.0+553+7a69454b | RLSA-2022:1915 |
| Rocky Linux:8 | mod_md | 1:2.0.8-8.module+el8.5.0+695+1fa8055e | RLSA-2022:1915 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Apache Software Foundation | Apache HTTP Server | Apache HTTP Server 2.4 2.4.17 to 2.4.48 |
References
- https://portswigger.net/research/http2
- https://github.com/apache/httpd/commit/ecebcc035ccd8d0e2984fe41420d9e944f456b3c.patch
- [httpd-cvs] 20210916 [httpd-site] branch main updated: Revert "Add descriptions for CVE-2021-33193 CVE-2021-36160" mailing-list
- [httpd-cvs] 20210916 [httpd-site] branch main updated: Add descriptions for CVE-2021-33193 CVE-2021-36160 mailing-list
- FEDORA-2021-5d2d4b6ac5 vendor-advisory
- FEDORA-2021-f94985afca vendor-advisory
- 20211124 Multiple Vulnerabilities in Apache HTTP Server Affecting Cisco Products: November 2021 vendor-advisory
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://security.netapp.com/advisory/ntap-20210917-0004/
- https://www.tenable.com/security/tns-2021-17
- https://www.oracle.com/security-alerts/cpuapr2022.html
- GLSA-202208-20 vendor-advisory
- [debian-lts-announce] 20230303 [SECURITY] [DLA 3351-1] apache2 security update mailing-list