CVE-2021-20181 (GCVE-0-2021-20181)
Vulnerability from cvelistv5 – Published: 2021-05-13 15:24 – Updated: 2024-08-03 17:30
VLAI
EPSS
VEX
Summary
A race condition flaw was found in the 9pfs server implementation of QEMU up to and including 5.2.0. This flaw allows a malicious 9p client to cause a use-after-free error, potentially escalating their privileges on the system. The highest threat from this vulnerability is to confidentiality, integrity as well as system availability.
Severity
7.5 (High)
CWE
- CWE-367 - >CWE-416
Assigner
References
5 references
| URL | Tags |
|---|---|
| https://www.zerodayinitiative.com/advisories/ZDI-… | x_refsource_MISC |
| https://lists.debian.org/debian-lts-announce/2021… | mailing-listx_refsource_MLIST |
| https://bugzilla.redhat.com/show_bug.cgi?id=1927007 | x_refsource_MISC |
| https://security.netapp.com/advisory/ntap-2021072… | x_refsource_CONFIRM |
| https://lists.debian.org/debian-lts-announce/2022… | mailing-listx_refsource_MLIST |
Impacted products
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"url": "https://security.netapp.com/advisory/ntap-20210720-0009/"
},
{
"name": "[debian-lts-announce] 20220905 [SECURITY] [DLA 3099-1] qemu security update",
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"cveId": "CVE-2021-20181",
"datePublished": "2021-05-13T15:24:15.000Z",
"dateReserved": "2020-12-17T00:00:00.000Z",
"dateUpdated": "2024-08-03T17:30:07.767Z",
"state": "PUBLISHED"
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"date": "2026-09-16",
"epss": "0.0032",
"percentile": "0.24934"
},
"fkie_nvd": {
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"descriptions": "[{\"lang\": \"en\", \"value\": \"A race condition flaw was found in the 9pfs server implementation of QEMU up to and including 5.2.0. This flaw allows a malicious 9p client to cause a use-after-free error, potentially escalating their privileges on the system. The highest threat from this vulnerability is to confidentiality, integrity as well as system availability.\"}, {\"lang\": \"es\", \"value\": \"Se encontr\\u00f3 un fallo de condici\\u00f3n de carrera en la implementaci\\u00f3n del servidor 9pfs de QEMU versiones hasta 5.2.0 incluy\\u00e9ndola.\u0026#xa0;Este fallo permite a un cliente 9p malicioso causar un error de uso de la memoria previamente liberada, escalando potencialmente sus privilegios en el sistema.\u0026#xa0;La mayor amenaza de esta vulnerabilidad es la confidencialidad, la integridad as\\u00ed como la disponibilidad del sistema\"}]",
"id": "CVE-2021-20181",
"lastModified": "2024-11-21T05:46:04.983",
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"published": "2021-05-13T16:15:07.653",
"references": "[{\"url\": \"https://bugzilla.redhat.com/show_bug.cgi?id=1927007\", \"source\": \"secalert@redhat.com\", \"tags\": [\"Issue Tracking\", \"Patch\", \"Third Party Advisory\"]}, {\"url\": \"https://lists.debian.org/debian-lts-announce/2021/02/msg00024.html\", \"source\": \"secalert@redhat.com\", \"tags\": [\"Mailing List\", \"Third Party Advisory\"]}, {\"url\": \"https://lists.debian.org/debian-lts-announce/2022/09/msg00008.html\", \"source\": \"secalert@redhat.com\", \"tags\": [\"Mailing List\", \"Third Party Advisory\"]}, {\"url\": \"https://security.netapp.com/advisory/ntap-20210720-0009/\", \"source\": \"secalert@redhat.com\", \"tags\": [\"Third Party Advisory\"]}, {\"url\": \"https://www.zerodayinitiative.com/advisories/ZDI-21-159/\", \"source\": \"secalert@redhat.com\", \"tags\": [\"Third Party Advisory\", \"VDB Entry\"]}, {\"url\": \"https://bugzilla.redhat.com/show_bug.cgi?id=1927007\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Issue Tracking\", \"Patch\", \"Third Party Advisory\"]}, {\"url\": \"https://lists.debian.org/debian-lts-announce/2021/02/msg00024.html\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Mailing List\", \"Third Party Advisory\"]}, {\"url\": \"https://lists.debian.org/debian-lts-announce/2022/09/msg00008.html\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Mailing List\", \"Third Party Advisory\"]}, {\"url\": \"https://security.netapp.com/advisory/ntap-20210720-0009/\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Third Party Advisory\"]}, {\"url\": \"https://www.zerodayinitiative.com/advisories/ZDI-21-159/\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Third Party Advisory\", \"VDB Entry\"]}]",
"sourceIdentifier": "secalert@redhat.com",
"vulnStatus": "Modified",
"weaknesses": "[{\"source\": \"secalert@redhat.com\", \"type\": \"Secondary\", \"description\": [{\"lang\": \"en\", \"value\": \"CWE-367\"}]}, {\"source\": \"nvd@nist.gov\", \"type\": \"Primary\", \"description\": [{\"lang\": \"en\", \"value\": \"CWE-362\"}]}]"
},
"microsoft_vex": {
"current_release_date": "2021-06-05T00:00:00.000Z",
"cve": "CVE-2021-20181",
"id": "msrc_CVE-2021-20181",
"initial_release_date": "2021-05-02T00:00:00.000Z",
"product_status:fixed": "1",
"product_status:known_affected": "1",
"source": "Microsoft CSAF VEX",
"status": "final",
"title": "A race condition flaw was found in the 9pfs server implementation of QEMU up to and including 5.2.0. This flaw allows a malicious 9p client to cause a use-after-free error potentially escalating their privileges on the system. The highest threat from this vulnerability is to confidentiality integrity as well as system availability.",
"url": "https://msrc.microsoft.com/csaf/vex/2021/msrc_cve-2021-20181.json",
"version": "1"
},
"nvd": "{\"cve\":{\"id\":\"CVE-2021-20181\",\"sourceIdentifier\":\"secalert@redhat.com\",\"published\":\"2021-05-13T16:15:07.653\",\"lastModified\":\"2024-11-21T05:46:04.983\",\"vulnStatus\":\"Modified\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"A race condition flaw was found in the 9pfs server implementation of QEMU up to and including 5.2.0. This flaw allows a malicious 9p client to cause a use-after-free error, potentially escalating their privileges on the system. The highest threat from this vulnerability is to confidentiality, integrity as well as system availability.\"},{\"lang\":\"es\",\"value\":\"Se encontr\u00f3 un fallo de condici\u00f3n de carrera en la implementaci\u00f3n del servidor 9pfs de QEMU versiones hasta 5.2.0 incluy\u00e9ndola.\u0026#xa0;Este fallo permite a un cliente 9p malicioso causar un error de uso de la memoria previamente liberada, escalando potencialmente sus privilegios en el sistema.\u0026#xa0;La mayor amenaza de esta vulnerabilidad es la confidencialidad, la integridad as\u00ed como la disponibilidad del sistema\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H\",\"baseScore\":7.5,\"baseSeverity\":\"HIGH\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"HIGH\",\"privilegesRequired\":\"HIGH\",\"userInteraction\":\"NONE\",\"scope\":\"CHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":0.8,\"impactScore\":6.0}],\"cvssMetricV2\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"2.0\",\"vectorString\":\"AV:L/AC:M/Au:N/C:C/I:C/A:C\",\"baseScore\":6.9,\"accessVector\":\"LOCAL\",\"accessComplexity\":\"MEDIUM\",\"authentication\":\"NONE\",\"confidentialityImpact\":\"COMPLETE\",\"integrityImpact\":\"COMPLETE\",\"availabilityImpact\":\"COMPLETE\"},\"baseSeverity\":\"MEDIUM\",\"exploitabilityScore\":3.4,\"impactScore\":10.0,\"acInsufInfo\":false,\"obtainAllPrivilege\":false,\"obtainUserPrivilege\":false,\"obtainOtherPrivilege\":false,\"userInteractionRequired\":false}]},\"weaknesses\":[{\"source\":\"secalert@redhat.com\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-367\"}]},{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-362\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:a:qemu:qemu:*:*:*:*:*:*:*:*\",\"versionEndIncluding\":\"5.2.0\",\"matchCriteriaId\":\"326C44E5-259C-47D1-B540-E153CD7C907C\"}]}]},{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*\",\"matchCriteriaId\":\"DEECE5FC-CACF-4496-A3E7-164736409252\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*\",\"matchCriteriaId\":\"07B237A9-69A3-4A9C-9DA0-4E06BD37AE73\"}]}]}],\"references\":[{\"url\":\"https://bugzilla.redhat.com/show_bug.cgi?id=1927007\",\"source\":\"secalert@redhat.com\",\"tags\":[\"Issue Tracking\",\"Patch\",\"Third Party Advisory\"]},{\"url\":\"https://lists.debian.org/debian-lts-announce/2021/02/msg00024.html\",\"source\":\"secalert@redhat.com\",\"tags\":[\"Mailing List\",\"Third Party Advisory\"]},{\"url\":\"https://lists.debian.org/debian-lts-announce/2022/09/msg00008.html\",\"source\":\"secalert@redhat.com\",\"tags\":[\"Mailing List\",\"Third Party Advisory\"]},{\"url\":\"https://security.netapp.com/advisory/ntap-20210720-0009/\",\"source\":\"secalert@redhat.com\",\"tags\":[\"Third Party Advisory\"]},{\"url\":\"https://www.zerodayinitiative.com/advisories/ZDI-21-159/\",\"source\":\"secalert@redhat.com\",\"tags\":[\"Third Party Advisory\",\"VDB Entry\"]},{\"url\":\"https://bugzilla.redhat.com/show_bug.cgi?id=1927007\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Issue Tracking\",\"Patch\",\"Third Party Advisory\"]},{\"url\":\"https://lists.debian.org/debian-lts-announce/2021/02/msg00024.html\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Mailing List\",\"Third Party Advisory\"]},{\"url\":\"https://lists.debian.org/debian-lts-announce/2022/09/msg00008.html\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Mailing List\",\"Third Party Advisory\"]},{\"url\":\"https://security.netapp.com/advisory/ntap-20210720-0009/\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Third Party Advisory\"]},{\"url\":\"https://www.zerodayinitiative.com/advisories/ZDI-21-159/\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Third Party Advisory\",\"VDB Entry\"]}]}}",
"redhat_vex": {
"aggregate_severity": "Moderate",
"current_release_date": "2026-06-28T07:05:03+00:00",
"cve": "CVE-2021-20181",
"id": "CVE-2021-20181",
"initial_release_date": "2021-01-14T00:00:00+00:00",
"product_status:known_not_affected": "105",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "qemu: 9pfs: TOCTOU privilege escalation vulnerability",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-20181.json",
"version": "3"
},
"suse_vex": {
"aggregate_severity": "important",
"current_release_date": "2026-08-22T17:07:02Z",
"cve": "CVE-2021-20181",
"id": "CVE-2021-20181",
"initial_release_date": "2023-02-15T03:47:38Z",
"product_status:known_affected": "370",
"product_status:known_not_affected": "249",
"product_status:recommended": "1977",
"source": "SUSE CSAF VEX",
"status": "interim",
"title": "SUSE CVE CVE-2021-20181",
"url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2021-20181.json",
"version": "43"
}
}
}
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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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