CVE-2021-33193: Request splitting via HTTP/2 method injection and mod_proxy
First published: Tue Jun 01 2021(Updated: )
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.
Credit: security@apache.org
| Affected Software | Affected Version | How to fix |
|---|---|---|
| redhat/jbcs-httpd24-httpd | <0:2.4.51-28.el8 | 0:2.4.51-28.el8 |
| redhat/jbcs-httpd24-httpd | <0:2.4.51-28.el7 | 0:2.4.51-28.el7 |
| redhat/httpd24-httpd | <0:2.4.34-23.el7.5 | 0:2.4.34-23.el7.5 |
| Apache HTTP server | >=2.4.17<=2.4.48 | |
| 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 |
Remedy
This flaw can be mitigated by disabling HTTP/2. More information available at: https://httpd.apache.org/docs/2.4/mod/mod_http2.html
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Reference Links
- https://www.cve.org/CVERecord?id=CVE-2021-33193 https://nvd.nist.gov/vuln/detail/CVE-2021-33193 https://portswigger.net/research/http2
- https://bugzilla.redhat.com/show_bug.cgi?id=1966728
- https://access.redhat.com/errata/RHSA-2022:7143
- https://access.redhat.com/errata/RHSA-2022:1915
- https://access.redhat.com/errata/RHSA-2022:7144
- https://access.redhat.com/errata/RHSA-2022:6753
- https://access.redhat.com/security/cve/cve-2021-33193
- https://github.com/apache/httpd/commit/ecebcc035ccd8d0e2984fe41420d9e944f456b3c.patch
- https://lists.apache.org/thread.html/re4162adc051c1a0a79e7a24093f3776373e8733abaff57253fef341d@%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/ree7519d71415ecdd170ff1889cab552d71758d2ba2904a17ded21a70@%3Ccvs.httpd.apache.org%3E
- https://lists.debian.org/debian-lts-announce/2023/03/msg00002.html
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/DSM6UWQICBJ2TU727RENU3HBKEAFLT6T/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/EUVJVRJRBW5QVX4OY3NOHZDQ3B3YOTSG/
- https://portswigger.net/research/http2
- https://security.gentoo.org/glsa/202208-20
- https://security.netapp.com/advisory/ntap-20210917-0004/
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQ
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://www.tenable.com/security/tns-2021-17
- https://bugzilla.redhat.com/show_bug.cgi/show_bug.cgi?id=1996514
- https://lists.apache.org/thread.html/re4162adc051c1a0a79e7a24093f3776373e8733abaff57253fef341d%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/ree7519d71415ecdd170ff1889cab552d71758d2ba2904a17ded21a70%40%3Ccvs.httpd.apache.org%3E
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DSM6UWQICBJ2TU727RENU3HBKEAFLT6T/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EUVJVRJRBW5QVX4OY3NOHZDQ3B3YOTSG/
Parent vulnerabilities
(Appears in the following advisories)
Frequently Asked Questions
What is CVE-2021-33193?
CVE-2021-33193 is a vulnerability found in Apache httpd mod_h2 that allows a crafted method sent through HTTP/2 to bypass validation and be forwarded by mod_proxy, leading to request splitting or cache poisoning.
Which versions of Apache HTTP Server are affected by CVE-2021-33193?
The vulnerability affects Apache HTTP Server versions 2.4.17 to 2.4.48.
What is the severity of CVE-2021-33193?
CVE-2021-33193 has a severity rating of 7.5, which is considered high.
How can I fix CVE-2021-33193?
To fix CVE-2021-33193, you should update Apache HTTP Server to version 2.4.49 or newer.
Where can I find more information about CVE-2021-33193?
You can find more information about CVE-2021-33193 on the following references: [Link 1](https://github.com/apache/httpd/commit/ecebcc035ccd8d0e2984fe41420d9e944f456b3c.patch), [Link 2](https://bugzilla.redhat.com/show_bug.cgi/show_bug.cgi?id=1996514), [Link 3](https://access.redhat.com/errata/RHSA-2022:1915)
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