CVE-2021-33193 (GCVE-0-2021-33193)
Vulnerability from cvelistv5 – Published: 2021-08-16 00:00 – Updated: 2024-08-03 23:42
VLAI
EPSS
VEX
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
References
13 references
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 |
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"cvssData": {
"accessComplexity": "LOW",
"accessVector": "NETWORK",
"authentication": "NONE",
"availabilityImpact": "NONE",
"baseScore": 5.0,
"confidentialityImpact": "NONE",
"integrityImpact": "PARTIAL",
"vectorString": "AV:N/AC:L/Au:N/C:N/I:P/A:N",
"version": "2.0"
},
"exploitabilityScore": 10.0,
"impactScore": 2.9,
"obtainAllPrivilege": false,
"obtainOtherPrivilege": false,
"obtainUserPrivilege": false,
"source": "nvd@nist.gov",
"type": "Primary",
"userInteractionRequired": false
}
],
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "NONE",
"baseScore": 7.5,
"baseSeverity": "HIGH",
"confidentialityImpact": "NONE",
"integrityImpact": "HIGH",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
"version": "3.1"
},
"exploitabilityScore": 3.9,
"impactScore": 3.6,
"source": "nvd@nist.gov",
"type": "Primary"
}
]
},
"published": "2021-08-16T08:15:11.480",
"references": [
{
"source": "security@apache.org",
"tags": [
"Patch"
],
"url": "https://github.com/apache/httpd/commit/ecebcc035ccd8d0e2984fe41420d9e944f456b3c.patch"
},
{
"source": "security@apache.org",
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"Patch"
],
"url": "https://lists.apache.org/thread.html/re4162adc051c1a0a79e7a24093f3776373e8733abaff57253fef341d%40%3Ccvs.httpd.apache.org%3E"
},
{
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"tags": [
"Patch"
],
"url": "https://lists.apache.org/thread.html/ree7519d71415ecdd170ff1889cab552d71758d2ba2904a17ded21a70%40%3Ccvs.httpd.apache.org%3E"
},
{
"source": "security@apache.org",
"tags": [
"Mailing List",
"Third Party Advisory"
],
"url": "https://lists.debian.org/debian-lts-announce/2023/03/msg00002.html"
},
{
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"tags": [
"Third Party Advisory"
],
"url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DSM6UWQICBJ2TU727RENU3HBKEAFLT6T/"
},
{
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},
{
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"url": "https://portswigger.net/research/http2"
},
{
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"tags": [
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"url": "https://security.gentoo.org/glsa/202208-20"
},
{
"source": "security@apache.org",
"tags": [
"Third Party Advisory"
],
"url": "https://security.netapp.com/advisory/ntap-20210917-0004/"
},
{
"source": "security@apache.org",
"tags": [
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{
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"tags": [
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{
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"url": "https://www.tenable.com/security/tns-2021-17"
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},
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},
{
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},
{
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"url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DSM6UWQICBJ2TU727RENU3HBKEAFLT6T/"
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{
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"url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EUVJVRJRBW5QVX4OY3NOHZDQ3B3YOTSG/"
},
{
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"url": "https://portswigger.net/research/http2"
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{
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{
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],
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},
{
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"Patch",
"Third Party Advisory"
],
"url": "https://www.oracle.com/security-alerts/cpujan2022.html"
},
{
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"tags": [
"Third Party Advisory"
],
"url": "https://www.tenable.com/security/tns-2021-17"
}
],
"sourceIdentifier": "security@apache.org",
"vulnStatus": "Analyzed",
"weaknesses": [
{
"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"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
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.
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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.
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.
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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.
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