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No exploitation reportedFix available

CVE-2021-33193

No exploitation reported by the sources we read.

  • Published2021-08-16
  • Fixed in2.4.49

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2021-08-1608:15CVE publishedNVD

Versions per branch

NVD · OSV
Apache HTTP Server
BranchAffectedFixed in
2.4≥ 2.4.17, < 2.4.492.4.49
Fedoraproject fedora
BranchAffectedFixed in
34.x= 34no fix published
35.x= 35no fix published
Debian debian linux
BranchAffectedFixed in
10.0= 10.0no fix published

3 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • apacheMageia:8all versions · fixed in 2.4.49-1.mga8
  • apache2Ubuntu:20.04:LTSall versions · fixed in 2.4.41-4ubuntu3.5
  • apache2Ubuntu:18.04:LTSall versions · fixed in 2.4.29-1ubuntu4.17
  • apache2SUSE:Linux Enterprise Software Development Kit 12 SP5all versions · fixed in 2.4.23-29.77.2
  • apache2SUSE:Linux Enterprise Server for SAP Applications 15 SP1all versions · fixed in 2.4.33-3.55.1
  • apache2SUSE:Linux Enterprise Server for SAP Applications 15all versions · fixed in 2.4.33-3.55.1
  • apache2SUSE:Linux Enterprise Server for SAP Applications 12 SP5all versions · fixed in 2.4.23-29.77.2
  • apache2SUSE:Linux Enterprise Server 15-LTSSall versions · fixed in 2.4.33-3.55.1

63 more package ranges on OSV.dev

Vendor advisories

  • CVE-2021-33193 Red Hat Product Security149 products fixed · 15 known affected

    httpd: Request splitting via HTTP/2 method injection and mod_proxy

    httpd as a component of Red Hat Enterprise Linux 6 · httpd-devel as a component of Red Hat Enterprise Linux 6 · httpd-manual as a component of Red Hat Enterprise Linux 6 · +12 more

  • RHSA-2022:7143 Red Hat Product Security27 products fixed

    Red Hat Security Advisory: Red Hat JBoss Core Services Apache HTTP Server 2.4.51 security update

  • RHSA-2022:7144 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat JBoss Core Services Apache HTTP Server 2.4.51 security update

  • RHSA-2022:6753 Red Hat Product Security36 products fixed

    Red Hat Security Advisory: httpd24-httpd security and bug fix update

  • RHSA-2022:1915 Red Hat Product Security85 products fixed

    Red Hat Security Advisory: httpd:2.4 security and bug fix update

Full record on NVD

Fix

  1. Update Apache HTTP Server to 2.4.49
  2. Vendor fix Red Hat Product Security RHSA-2022:7143 · 27 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Applications using the APR libraries, such as httpd, must be restarted for this update to take effect. After installing the updated packages, the http…
  3. Vendor fix Red Hat Product Security RHSA-2022:7144 · 1 productFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
  4. Vendor fix Red Hat Product Security RHSA-2022:6753 · 36 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 After installing the updated packages, the httpd daemon will be restarted automatically.
  5. Workaround from the vendor Red Hat Product Security RHSA-2022:7143 · 156 productsThis flaw can be mitigated by disabling HTTP/2. More information available at: https://httpd.apache.org/docs/2.4/mod/mod_http2.html
  6. No fix planned, says the vendor Red Hat Product Security CVE-2021-33193 · 15 productsOut of support scope

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Published
2021-08-16
Last Modified
2026-06-17
NVD status
Analyzed
GitHub Advisory
GHSA-p9fg-6rr5-38xc

Frequently asked questions

What is CVE-2021-33193?

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.

Is CVE-2021-33193 actively exploited?

Active exploitation of CVE-2021-33193 has not been confirmed. Its EPSS score was 46.2% on 2026-11-09, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-33193?

CVE-2021-33193 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

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Sources for this record