CVE-2021-33193

Name: CVE-2021-33193
Creator: NVD / NIST
Published: 2021-08-16T08:15:11.48+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 46.18%

Last modified Jun 17, 2026

CVE-2021-33193 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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.. EPSS estimates a 46.18% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS Probability

46.18%

98.7th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Debian	Debian Linux	10.0
Apache	Http Server	>= 2.4.17, < 2.4.49
Fedoraproject	Fedora	34
Fedoraproject	Fedora	35
Tenable	Tenable.Sc	<= 5.19.1
Oracle	Secure Backup	< 18.1.0.1.0
Oracle	Zfs Storage Appliance Kit	8.8

References

https://github.com/apache/httpd/commit/ecebcc035ccd8d0e2984fe41420d9e944f456b3c.patchPatch
https://lists.apache.org/thread.html/re4162adc051c1a0a79e7a24093f3776373e8733abaff57253fef341d%40%3Ccvs.httpd.apache.org%3EPatch
https://lists.apache.org/thread.html/ree7519d71415ecdd170ff1889cab552d71758d2ba2904a17ded21a70%40%3Ccvs.httpd.apache.org%3EPatch
https://lists.debian.org/debian-lts-announce/2023/03/msg00002.htmlMailing List, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DSM6UWQICBJ2TU727RENU3HBKEAFLT6T/Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EUVJVRJRBW5QVX4OY3NOHZDQ3B3YOTSG/Third Party Advisory
https://portswigger.net/research/http2Exploit, Third Party Advisory
https://security.gentoo.org/glsa/202208-20Third Party Advisory
https://security.netapp.com/advisory/ntap-20210917-0004/Third Party Advisory
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQThird Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.htmlPatch, Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.htmlPatch, Third Party Advisory
https://www.tenable.com/security/tns-2021-17Third Party Advisory
https://github.com/apache/httpd/commit/ecebcc035ccd8d0e2984fe41420d9e944f456b3c.patchPatch
https://lists.apache.org/thread.html/re4162adc051c1a0a79e7a24093f3776373e8733abaff57253fef341d%40%3Ccvs.httpd.apache.org%3EPatch
https://lists.apache.org/thread.html/ree7519d71415ecdd170ff1889cab552d71758d2ba2904a17ded21a70%40%3Ccvs.httpd.apache.org%3EPatch
https://lists.debian.org/debian-lts-announce/2023/03/msg00002.htmlMailing List, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DSM6UWQICBJ2TU727RENU3HBKEAFLT6T/Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EUVJVRJRBW5QVX4OY3NOHZDQ3B3YOTSG/Third Party Advisory
https://portswigger.net/research/http2Exploit, Third Party Advisory
https://security.gentoo.org/glsa/202208-20Third Party Advisory
https://security.netapp.com/advisory/ntap-20210917-0004/Third Party Advisory
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQThird Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.htmlPatch, Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.htmlPatch, Third Party Advisory
https://www.tenable.com/security/tns-2021-17Third Party Advisory

Timeline

Published: Aug 16, 2021
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2021-33193?

How severe is CVE-2021-33193?

CVE-2021-33193 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 46.18% probability of exploitation in the next 30 days.

How do I fix CVE-2021-33193?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-33193?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST