01 Record

CVE-2021-33193

Request splitting via HTTP/2 method injection and mod_proxy

UnratedPUBLISHEDCNA: apache

CNA base scoreUnratedNo CNA CVSS vector

View raw JSON

02 Description

Request splitting via HTTP/2 method injection and mod_proxy

03 Exploitation and scoring

Exploitation: Not assessed. CISA has not published an exploitation assessment for this record, and it is not in the KEV catalog. That is an absence of assessment, not a finding of no risk.
SSVC decision: Not assessed by CISA
EPSS probability: 46.17% probability of exploitation activity in the next 30 days.
EPSS percentile: Equal to or higher than the score of 98.7% of scored records. A rank, not a probability.
NVD base score: 7.5 (CVSS v3.x), scored by the NVD independently of the CNA.
NVD CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
NVD analysis status: Analyzed. NVD last modified this record on 2026-06-17.
Red Hat severity: Moderate. Red Hat's rating for its own products, not a CVSS rating.

Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.

04 Metadata

Published

2021-08-16 00:00Z5 YR AGO

Last updated

2024-08-03 23:42Z2 YR AGO

Reserved

2021-05-19

Assigning CNA

apache

Record state

PUBLISHED

Severity

Not rated by the issuing CNA

CNA CVSS vector

Not published by the issuing CNA

Weaknesses

CWE-476NULL Pointer DereferenceBase

Data version

5.1

Document digest

e23c35ab747aa21ee46e4ee446960cb85d5ed8423d4b6111807cf1ea229d9ba5

05 Affected products

VendorProductVersionsPlatforms

Apache Software FoundationApache HTTP ServerApache HTTP Server 2.4 2.4.17 to 2.4.48—

06 References

portswigger.nethttps://portswigger.net/research/http2
github.comhttps://github.com/apache/httpd/commit/ecebcc035ccd8d0e2984fe41420d9e944f456b3c.patch
lists.apache.org[httpd-cvs] 20210916 [httpd-site] branch main updated: Revert "Add descriptions for CVE-2021-33193 CVE-2021-36160"https://lists.apache.org/thread.html/re4162adc051c1a0a79e7a24093f3776373e8733abaff57253fef341d%40%3Ccvs.httpd.apache.org%3Emailing-list
lists.apache.org[httpd-cvs] 20210916 [httpd-site] branch main updated: Add descriptions for CVE-2021-33193 CVE-2021-36160https://lists.apache.org/thread.html/ree7519d71415ecdd170ff1889cab552d71758d2ba2904a17ded21a70%40%3Ccvs.httpd.apache.org%3Emailing-list
lists.fedoraproject.orgFEDORA-2021-5d2d4b6ac5https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DSM6UWQICBJ2TU727RENU3HBKEAFLT6T/vendor-advisory
lists.fedoraproject.orgFEDORA-2021-f94985afcahttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EUVJVRJRBW5QVX4OY3NOHZDQ3B3YOTSG/vendor-advisory
tools.cisco.com20211124 Multiple Vulnerabilities in Apache HTTP Server Affecting Cisco Products: November 2021https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQvendor-advisory
www.oracle.comhttps://www.oracle.com/security-alerts/cpujan2022.html
security.netapp.comhttps://security.netapp.com/advisory/ntap-20210917-0004/
www.tenable.comhttps://www.tenable.com/security/tns-2021-17
www.oracle.comhttps://www.oracle.com/security-alerts/cpuapr2022.html
security.gentoo.orgGLSA-202208-20https://security.gentoo.org/glsa/202208-20vendor-advisory
lists.debian.org[debian-lts-announce] 20230303 [SECURITY] [DLA 3351-1] apache2 security updatehttps://lists.debian.org/debian-lts-announce/2023/03/msg00002.htmlmailing-list

07 Fixed in

AlmaLinux 8

httpd
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
httpd-devel
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
httpd-filesystem
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
httpd-manual
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
httpd-tools
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
mod_http2
Fixed in 1.15.7-5.module_el8.6.0+2872+fe0ff7aa
mod_ldap
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
mod_md
Fixed in 1:2.0.8-8.module_el8.6.0+2872+fe0ff7aa
mod_proxy_html
Fixed

A version is affected if any line below covers it.
- Affected before 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 1:2.4.37-47.module_el8.6.0+2935+fb177b09.2
mod_session
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
mod_ssl
Fixed

A version is affected if any line below covers it.
- Affected before 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 1:2.4.37-47.module_el8.6.0+2935+fb177b09.2

Arch Linux

apache
Fixed in 2.4.49-1

Source: Arch Linux Security Tracker, the Arch Linux security team. Reformatted by exploit.cc.

CloudLinux 8

httpd
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
httpd-devel
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
httpd-filesystem
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
httpd-manual
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
httpd-tools
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
mod_http2
Fixed in 1.15.7-5.module_el8.6.0+2872+fe0ff7aa
mod_ldap
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
mod_md
Fixed in 1:2.0.8-8.module_el8.6.0+2872+fe0ff7aa
mod_proxy_html
Fixed

A version is affected if any line below covers it.
- Affected before 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 1:2.4.37-47.module_el8.6.0+2935+fb177b09.2
mod_session
Fixed

A version is affected if any line below covers it.
- Affected before 2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 2.4.37-47.module_el8.6.0+2935+fb177b09.2
mod_ssl
Fixed

A version is affected if any line below covers it.
- Affected before 1:2.4.37-47.module_el8.6.0+2872+fe0ff7aa.1.alma
- Affected before 1:2.4.37-47.module_el8.6.0+2935+fb177b09.2

Derived from AlmaLinux 8. Partial coverage: only packages taken from AlmaLinux 8 are listed.

Debian 12

apache2
Fixed in 2.4.48-4

Source: Debian Security Tracker, the Debian security team. Received through OSV.dev. Reformatted by exploit.cc.

Debian 13

apache2
Fixed in 2.4.48-4

Source: Debian Security Tracker, the Debian security team. Received through OSV.dev. Reformatted by exploit.cc.

Debian 14

apache2
Fixed in 2.4.48-4

Source: Debian Security Tracker, the Debian security team. Received through OSV.dev. Reformatted by exploit.cc.

Ubuntu 18.04 LTS

apache2
Fixed in 2.4.29-1ubuntu4.17

Source: Ubuntu, Canonical Ltd. Licensed under CC BY-SA 4.0. Received through OSV.dev. Reformatted by exploit.cc.

Ubuntu 20.04 LTS

apache2
Fixed in 2.4.41-4ubuntu3.5

Source: Ubuntu, Canonical Ltd. Licensed under CC BY-SA 4.0. Received through OSV.dev. Reformatted by exploit.cc.

A release or ecosystem missing from this list has no record here. It may be unaffected or not covered by the source. Source notices and licences.