CVE-2021-33193
HIGH7.5EPSS 0.61%Request splitting via HTTP/2 method injection and mod_proxy
Published: 8/16/2021Modified: 4/28/2026
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 (3)
- Alpine/apache2from 0, < 2.4.49-r0
- Bitnami/apache>= 2.4.17, < 2.4.49
- Debian/apache2from 0, < 2.4.48-3.1+deb11u1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N |
References (16)
- ADVISORYhttps://security.alpinelinux.org/vuln/CVE-2021-33193
- ADVISORYhttps://security-tracker.debian.org/tracker/CVE-2021-33193
- WEBhttps://github.com/apache/httpd/commit/ecebcc035ccd8d0e2984fe41420d9e944f456b3c.patch
- WEBhttps://lists.apache.org/thread.html/re4162adc051c1a0a79e7a24093f3776373e8733abaff57253fef341d%40%3Ccvs.httpd.apache.org%3E
- WEBhttps://lists.apache.org/thread.html/ree7519d71415ecdd170ff1889cab552d71758d2ba2904a17ded21a70%40%3Ccvs.httpd.apache.org%3E
- WEBhttps://lists.debian.org/debian-lts-announce/2023/03/msg00002.html
- WEBhttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DSM6UWQICBJ2TU727RENU3HBKEAFLT6T/
- WEBhttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EUVJVRJRBW5QVX4OY3NOHZDQ3B3YOTSG/
- WEBhttps://nvd.nist.gov/vuln/detail/CVE-2021-33193
- WEBhttps://portswigger.net/research/http2
- WEBhttps://security.gentoo.org/glsa/202208-20
- WEBhttps://security.netapp.com/advisory/ntap-20210917-0004/
- WEBhttps://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQ
- WEBhttps://www.oracle.com/security-alerts/cpuapr2022.html
- WEBhttps://www.oracle.com/security-alerts/cpujan2022.html
- WEBhttps://www.tenable.com/security/tns-2021-17