Vulnerability-Lookup

CVE-2021-33193 (GCVE-0-2021-33193)

Vulnerability from cvelistv5 – Published: 2021-08-16 00:00 – Updated: 2024-08-03 23:42

Title

Request splitting via HTTP/2 method injection and mod_proxy

Summary

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.

Severity

No CVSS data available.

CWE

Request Splitting

Assigner

apache mitre root

References

13 references

URL	Tags
https://portswigger.net/research/http2
https://github.com/apache/httpd/commit/ecebcc035c…
https://lists.apache.org/thread.html/re4162adc051…	mailing-list
https://lists.apache.org/thread.html/ree7519d7141…	mailing-list
https://lists.fedoraproject.org/archives/list/pac…	vendor-advisory
https://lists.fedoraproject.org/archives/list/pac…	vendor-advisory
https://tools.cisco.com/security/center/content/C…	vendor-advisory
https://www.oracle.com/security-alerts/cpujan2022.html
https://security.netapp.com/advisory/ntap-2021091…
https://www.tenable.com/security/tns-2021-17
https://www.oracle.com/security-alerts/cpuapr2022.html
https://security.gentoo.org/glsa/202208-20	vendor-advisory
https://lists.debian.org/debian-lts-announce/2023…	mailing-list

Impacted products

1 product

Vendor	Product	Version	CPE status
Apache Software Foundation	Apache HTTP Server	Affected: Apache HTTP Server 2.4 2.4.17 to 2.4.48	guessed

Credits

Reported by James Kettle of PortSwigger

Show details on NVD website

JSON

To clipboard

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        "sourceIdentifier": "security@apache.org",
        "vulnStatus": "Analyzed",
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          {
            "description": [
              {
                "lang": "en",
                "value": "NVD-CWE-Other"
              }
            ],
            "source": "nvd@nist.gov",
            "type": "Primary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-06-28T06:25:16+00:00",
      "cve": "CVE-2021-33193",
      "id": "CVE-2021-33193",
      "initial_release_date": "2021-08-05T00:00:00+00:00",
      "product_status:fixed": "149",
      "product_status:known_affected": "15",
      "product_status:known_not_affected": "143",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "httpd: Request splitting via HTTP/2 method injection and mod_proxy",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-33193.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "critical",
      "current_release_date": "2026-08-31T02:03:46Z",
      "cve": "CVE-2021-33193",
      "id": "CVE-2021-33193",
      "initial_release_date": "2023-02-15T03:40:36Z",
      "product_status:known_affected": "498",
      "product_status:known_not_affected": "4",
      "product_status:recommended": "297",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2021-33193",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2021-33193.json",
      "version": "36"
    }
  }
}

SUSE-SU-2021:3335-1

Vulnerability from csaf_suse - Published: 2021-10-12 06:19 - Updated: 2021-10-12 06:19

Summary

Security update for apache2

Severity

Important

Scope

5 vulnerabilities in this advisory, including CVE-2021-33193.

CVE-2021-33193

9.1 (Critical)


                
                  CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Recommended: 125 products

Open the full advisory

UBUNTU-CVE-2021-33193 (CVE-2021-33193)

Vulnerability from osv_ubuntu – Published: 2021-08-16 08:15 – Updated: 2026-04-22 07:40 – Source website

Details

Severity

7.5 (High)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2021-33193	REPORT
	https://portswigger.net/research/http2	REPORT
	https://ubuntu.com/security/notices/USN-5090-1	ADVISORY
	https://www.cve.org/CVERecord?id=CVE-2021-33193	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "availability": "No subscription required",
        "binaries": [
          {
            "binary_name": "apache2",
            "binary_version": "2.4.29-1ubuntu4.17"
          },
          {
            "binary_name": "apache2-bin",
            "binary_version": "2.4.29-1ubuntu4.17"
          },
          {
            "binary_name": "apache2-data",
            "binary_version": "2.4.29-1ubuntu4.17"
          },
          {
            "binary_name": "apache2-suexec-custom",
            "binary_version": "2.4.29-1ubuntu4.17"
          },
          {
            "binary_name": "apache2-suexec-pristine",
            "binary_version": "2.4.29-1ubuntu4.17"
          },
          {
            "binary_name": "apache2-utils",
            "binary_version": "2.4.29-1ubuntu4.17"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:18.04:LTS",
        "name": "apache2",
        "purl": "pkg:deb/ubuntu/apache2@2.4.29-1ubuntu4.17?arch=source\u0026distro=bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.4.29-1ubuntu4.17"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.4.27-2ubuntu3",
        "2.4.29-1ubuntu1",
        "2.4.29-1ubuntu2",
        "2.4.29-1ubuntu3",
        "2.4.29-1ubuntu4",
        "2.4.29-1ubuntu4.1",
        "2.4.29-1ubuntu4.2",
        "2.4.29-1ubuntu4.3",
        "2.4.29-1ubuntu4.4",
        "2.4.29-1ubuntu4.5",
        "2.4.29-1ubuntu4.6",
        "2.4.29-1ubuntu4.7",
        "2.4.29-1ubuntu4.8",
        "2.4.29-1ubuntu4.10",
        "2.4.29-1ubuntu4.11",
        "2.4.29-1ubuntu4.12",
        "2.4.29-1ubuntu4.13",
        "2.4.29-1ubuntu4.14",
        "2.4.29-1ubuntu4.16"
      ]
    },
    {
      "ecosystem_specific": {
        "availability": "No subscription required",
        "binaries": [
          {
            "binary_name": "apache2",
            "binary_version": "2.4.41-4ubuntu3.5"
          },
          {
            "binary_name": "apache2-bin",
            "binary_version": "2.4.41-4ubuntu3.5"
          },
          {
            "binary_name": "apache2-data",
            "binary_version": "2.4.41-4ubuntu3.5"
          },
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            "binary_name": "apache2-suexec-custom",
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          },
          {
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            "binary_version": "2.4.41-4ubuntu3.5"
          },
          {
            "binary_name": "apache2-utils",
            "binary_version": "2.4.41-4ubuntu3.5"
          },
          {
            "binary_name": "libapache2-mod-md",
            "binary_version": "2.4.41-4ubuntu3.5"
          },
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            "binary_name": "libapache2-mod-proxy-uwsgi",
            "binary_version": "2.4.41-4ubuntu3.5"
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      "package": {
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        "2.4.41-4ubuntu3.3",
        "2.4.41-4ubuntu3.4"
      ]
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  "id": "UBUNTU-CVE-2021-33193",
  "modified": "2026-04-22T07:40:04Z",
  "published": "2021-08-16T08:15:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2021-33193"
    },
    {
      "type": "REPORT",
      "url": "https://portswigger.net/research/http2"
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    {
      "type": "ADVISORY",
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      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2021-33193"
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    "USN-5090-1"
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  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
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    "CVE-2021-33193"
  ]
}

WID-SEC-W-2022-0722

Vulnerability from csaf_certbund - Published: 2021-08-16 22:00 - Updated: 2023-03-05 23:00

Summary

Apache HTTP Server: Schwachstelle ermöglicht Denial of Service

Severity

Mittel

Scope

1 vulnerability in this advisory, including CVE-2021-33193.

CVE-2021-33193

Es existiert eine Schwachstelle in Apache HTTP Server. Eine über HTTP/2 gesendete methode wird nur ungenügend validiert und von mod_proxy weitergeleitet, was zu einem Request Splitting oder Cache Poisoning führen und in der Folge zu einem Denial of Service führen kann. Ein entfernter anonymer Angreifer kann diese Schwachstelle ausnutzen, um einen Denial of Service zu verursachen.

Known affected: 22 products

Open the full advisory

WID-SEC-W-2024-1591

Vulnerability from csaf_certbund - Published: 2024-07-10 22:00 - Updated: 2024-11-11 23:00

Summary

Juniper JUNOS: Mehrere Schwachstellen

Severity

Mittel

Scope

281 vulnerabilities in this advisory, including CVE-2021-33193.

CVE-2021-33193

Es existieren mehrere Schwachstellen in verschiedenen Juniper-Produkten. Ursachen sind unter Anderem Ungenügende Eingabeüberprüfungen, Unsachgemäße Überprüfung und Verarbeitung von Paketen, fehlende Speicherfreigaben, fehlerhafte Behandlung von Ausnahmen, Unsachgemäße Speicherbehandlung, unkontrollierter Ressourcenverbrauch, Klartextspeicherung von Daten und Pufferüberläufe. Diese Schwachstellen ermöglichen Angreifern Denial of Service Zustände zu verursachen, Informationen offenzulegen, Code auszuführen, Privilegien zu erweitern und Sicherheitsmechanismen inklusive der Firewall Funktionalität zu umgehen. Zu einer erfolgreichen Ausnutzung einiger dieser Schwachstellen ist eine Anmeldung oder eine Interaktion des Nutzers notwendig.

Known affected: 1 product

Open the full advisory

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2021-33193 (GCVE-0-2021-33193)

SUSE-SU-2021:3335-1

UBUNTU-CVE-2021-33193 (CVE-2021-33193)

WID-SEC-W-2022-0722

WID-SEC-W-2024-1591

Tags

Sightings

Nomenclature

Related by attack behaviour