CVE-2021-33193

mediumpriority · attend · 46EPSS 0.462 · 99 %ileDEEURUUS

grimoire priorityP1 · Urgent

Exploitable?

—

no known exploitation

Likely / severe?

46.2% (99th) EPSS

CVSS 5 · medium

Is it mine?

26 products

Check your exposure

Who says so?

7 sources

cnnvd · enisa_euvd · fstec_bdu · cert_bund

EPSS · scored 2026-10-27

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.

remediations

Vendor fix, mitigation, or workaround guidance, as published by each source.

A vendor fix is available.

FixedCisco Firepower Extensible Operating System (FXOS)cisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
FixedCisco TelePresence Video Communication Server (VCS) Expresswaycisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
WorkaroundCisco Firepower Extensible Operating System (FXOS)cisco_csaf
Any workarounds will be documented in the product-specific Cisco bugs, which are identified in the Vulnerable Products ["#vp"] section of this advisory.
WorkaroundCisco TelePresence Video Communication Server (VCS) Expresswaycisco_csaf
Any workarounds will be documented in the product-specific Cisco bugs, which are identified in the Vulnerable Products ["#vp"] section of this advisory.

cvss

Technical severity, 0–10. One row per scoring source.

7.5

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 4.8–7.5

v2.05mediumAV:N/AC:L/Au:N/C:N/I:P/A:Nprimary · NVD / NIST USexploitability 10 · impact 2.9

v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:Nprimary · NVD / NIST USexploitability 3.9 · impact 3.6

v3.14.8mediumAV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:Nsecondary · FSTEC (BDU) RU

v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N/E:Hsecondary · CVSS-BT (t0sche)

v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:Nsecondary · Cisco PSIRT US

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-444US

affected products (26)

Products and version ranges known to be affected.

Juniper JUNOSall versionscert_bundDEcpe:/o:juniper:junos:-
Cisco Cisco Firepower Extensible Operating System (FXOS)all versionscisco_csafUS
Cisco Cisco TelePresence Video Communication Server (VCS) Expresswayall versionscisco_csafUS
Apache Software Foundation Apache HTTP Server≤ Apache HTTP Server 2.4 2.4.17 to 2.4.48enisa_euvdEU
Apache Software Foundation HTTP Server2.4 → 2.4.48fstec_bduRU
АО «ИВК» Альт 8 СПall versionsfstec_bduRU
АО «Концерн ВНИИНС» ОС ОН «Стрелец»≤ 16.01.2023fstec_bduRU
АО «НППКТ» ОСОН ОСнова Оnyx≤ 2.3fstec_bduRU
АО «НТЦ ИТ РОСА» ROSA Virtualization≤ 2.1fstec_bduRU
АО «НТЦ ИТ РОСА» ROSA Virtualization 3.0≤ 3.0fstec_bduRU
ООО «РусБИТех-Астра» Astra Linux Common Edition≤ 2.12 «Орёл»fstec_bduRU
ООО «РусБИТех-Астра» Astra Linux Special Edition≤ 1.6 «Смоленск»fstec_bduRU
ООО «РусБИТех-Астра» Astra Linux Special Edition≤ 4.7fstec_bduRU
ООО «РусБИТех-Астра» Astra Linux Special Edition≤ 1.7fstec_bduRU
ООО «РусБИТех-Астра» Astra Linux Special Edition для «Эльбрус»≤ 8.1 «Ленинград»fstec_bduRU
Сообщество свободного программного обеспечения Debian GNU/Linux≤ 9fstec_bduRU
Сообщество свободного программного обеспечения Debian GNU/Linux≤ 10fstec_bduRU
Сообщество свободного программного обеспечения Debian GNU/Linux≤ 11fstec_bduRU
apache http server2.4.17 → 2.4.49nvdUScpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:*
debian debian linux= 10.0nvdUScpe:2.3:o:debian:debian_linux:*:*:*:*:*:*:*:*

showing 20 of 26

advisories (4)

Vendor and ecosystem advisories describing this.

WID-SEC-W-2022-0722Apache HTTP Server: Schwachstelle ermöglicht Denial of ServiceDeutsch2021-08-16csaf · cert_bundDE
Ein entfernter, anonymer Angreifer kann eine Schwachstelle in Apache HTTP Server ausnutzen, um einen Denial of Service Angriff durchzuführen.
WID-SEC-W-2024-1591Juniper JUNOS: Mehrere SchwachstellenDeutsch2024-07-10csaf · cert_bundDE
Ein Angreifer kann mehrere Schwachstellen in Juniper JUNOS ausnutzen, um einen Denial of Service zu verursachen, Informationen offenzulegen, Privilegien zu erweitern und Sicherheitsmechanismen inklusive zu umgehen.
cisco-sa-apache-httpd-2.4.49-VWL69sWQMultiple Vulnerabilities in Apache HTTP Server Affecting Cisco Products: November 20212021-11-24csaf · cisco_csafUS
On September 16, 2021, the Apache Software Foundation disclosed five vulnerabilities affecting the Apache HTTP Server (httpd) 2.4.48 and earlier releases. For a description of these vulnerabilities, see the Apache HTTP Server 2.4.49 section ["https://httpd.apache.org/security/vulnerabilities_24.html#2.4.49"] of the Apache HTTP Server 2.4 vulnerabilities webpage. This advisory will be updated as additional information becomes available.
BIT-apache-2021-33193Request splitting via HTTP/2 method injection and mod_proxy2024-03-06vendor · osvUS
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.

also known as (4)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd fstec_bdu cert_bund cisco_csaf nvd osv NVD CVE.org MITRE

published 2021-08-16modified 2026-06-17

references (63)

External citations — patches, advisories, analysis.

scry

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