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CVE-2021-33193

Request splitting via HTTP/2 method injection and mod_proxy

Published: Aug 16, 2021Updated: May 1, 2025 Sources: CVE List NVD BDUNVD-CWE-Other
NVD MITRE
7.5CVSSHIGH
EPSS Score
46.2%
Top 1.3%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Am I actually vulnerable?1 Nuclei template available — see how to check your systems. How to verify

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.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:HA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:HIntegrity
High
A:NAvailability
None
Open in CVSS calculator →

Weaknesses

NVD-CWE-Other

Affected Products

Debian GNU/LinuxСообщество свободного программного обеспечения
On-premOS
Operating Systems / linux-distro
Astra Linux Special EditionООО «РусБИТех-Астра»
On-premOS
Operating Systems / linux-distro
Astra Linux Common EditionООО «РусБИТех-Астра»
On-premOS
Operating Systems / linux-distro
Astra Linux Special Edition для «Эльбрус»ООО «РусБИТех-Астра»
On-premOS
Operating Systems / linux-distro
HTTP ServerApache Software Foundation
On-premWeb App
Networking Infrastructure / load-balancer-proxy
сообщество свободного программного обеспеченияoss-projectOperating Systemsaka сообщество свободного программного обеспечения, fsf
ооо «русбитех-астра»commercialRUOperating Systemsaka rusbitech-astra
apache software foundationoss-projectUSWeb & CMS Pluginsaka apache foundation
and 12 more affected products View all →

Exploitability

Official Patch Available

References

https://portswigger.net/research/http2
portswigger.net
https://github.com/apache/httpd/commit/ecebcc035ccd8d0e2984fe41420d9e944f456b3c
github.com
https://habr.com/ru/news/t/571694/
habr.com
and 32 more references View all →

Timeline

Published
Aug 16, 2021
Last Updated
May 1, 2025

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