Exploitation evidence
Known exploited · CISA KEV listed
Added 2026-04-13. Ransomware campaign use: Known.
CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
CISA due date: 2026-04-27. This is the catalog’s deadline, not an assessment of your organization’s exposure.
KEV checked 13 Nov 2026, 00:20 Jerusalem · Original catalog ↗Reported products and versions
Microsoft / Microsoft Exchange Server 2013 Cumulative Update 23
Default status: Not specified
- affected: 15.00.0 to < 15.00.1497.047 (custom)
Microsoft / Microsoft Exchange Server 2016 Cumulative Update 23
Default status: Not specified
- affected: 15.01.0 to < 15.01.2507.021 (custom)
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 11
Default status: Not specified
- affected: 15.02.0 to < 15.02.0986.041 (custom)
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 12
Default status: Not specified
- affected: 15.02.0 to < 15.02.1118.025 (custom)
Fixes and workarounds
No explicit solution text in the downloaded CVE record. Consult the vendor advisory; unaffected version ranges are shown above as reported, not inferred as a patch recommendation.
Sources and related reporting
CVE Program record ↗ · Download tracked evidence as JSON
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529
- https://www.microsoft.com/en-us/security/blog/2026/04/06/storm-1175-focuses-gaze-on-vulnerable-web-facing-assets-in-high-tempo-medusa-ransomware-operations/
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-21529
Observed change timeline
History begins when Egret first downloads each source. It is not the complete upstream CVE history.
12 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-12",
"epss": 0.59294,
"percentile": 0.99132
}10 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-10",
"epss": 0.59294,
"percentile": 0.99127
}09 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-09",
"epss": 0.59294,
"percentile": 0.99125
}08 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-08",
"epss": 0.59294,
"percentile": 0.99125
}07 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-07",
"epss": 0.59294,
"percentile": 0.99124
}06 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-06",
"epss": 0.59294,
"percentile": 0.99123
}06 Nov 2026, 06:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-05",
"epss": 0.59294,
"percentile": 0.99122
}05 Nov 2026, 00:20 Jerusalem · CVE Program record changed
Stored CNA snapshot at this observation.
{
"containers": {
"adp": [
{
"providerMetadata": {
"dateUpdated": "2024-08-02T09:44:01.279Z",
"orgId": "af854a3a-2127-422b-91ae-364da2661108",
"shortName": "CVE"
},
"references": [
{
"name": "Microsoft Exchange Server Remote Code Execution Vulnerability",
"tags": [
"vendor-advisory",
"x_transferred"
],
"url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529"
}
],
"title": "CVE Program Container"
},
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2023-21529",
"options": [
{
"Exploitation": "active"
},
{
"Automatable": "no"
},
{
"Technical Impact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2023-02-15T00:00:00+00:00",
"version": "2.0.3"
},
"type": "ssvc"
}
},
{
"other": {
"content": {
"dateAdded": "2026-04-13",
"reference": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-21529"
},
"type": "kev"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-04-14T03:55:24.065Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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},
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],
"url": "https://www.microsoft.com/en-us/security/blog/2026/04/06/storm-1175-focuses-gaze-on-vulnerable-web-facing-assets-in-high-tempo-medusa-ransomware-operations/"
},
{
"tags": [
"government-resource"
],
"url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-21529"
}
],
"timeline": [
{
"lang": "en",
"time": "2026-04-13T00:00:00.000Z",
"value": "CVE-2023-21529 added to CISA KEV"
}
],
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
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"x64-based Systems"
],
"product": "Microsoft Exchange Server 2013 Cumulative Update 23",
"vendor": "Microsoft",
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},
{
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],
"product": "Microsoft Exchange Server 2016 Cumulative Update 23",
"vendor": "Microsoft",
"versions": [
{
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"status": "affected",
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]
},
{
"platforms": [
"x64-based Systems"
],
"product": "Microsoft Exchange Server 2019 Cumulative Update 11",
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"status": "affected",
"version": "15.02.0",
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}
]
},
{
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"x64-based Systems"
],
"product": "Microsoft Exchange Server 2019 Cumulative Update 12",
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{
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"status": "affected",
"version": "15.02.0",
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}
]
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],
"cpeApplicability": [
{
"nodes": [
{
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{
"criteria": "cpe:2.3:a:microsoft:exchange_server:*:cumulative_update_12:*:*:*:*:*:*",
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"vulnerable": true
},
{
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"vulnerable": true
},
{
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"versionEndExcluding": "15.00.1497.047",
"versionStartIncluding": "15.00.0",
"vulnerable": true
},
{
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"versionEndExcluding": "15.01.2507.021",
"versionStartIncluding": "15.01.0",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
]
}
],
"datePublic": "2023-02-14T08:00:00.000Z",
"descriptions": [
{
"lang": "en-US",
"value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 8.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C",
"version": "3.1"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en-US",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-502",
"description": "CWE-502: Deserialization of Untrusted Data",
"lang": "en-US",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-19T16:26:33.854Z",
"orgId": "f38d906d-7342-40ea-92c1-6c4a2c6478c8",
"shortName": "microsoft"
},
"references": [
{
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"tags": [
"vendor-advisory",
"patch"
],
"url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529"
}
],
"title": "Microsoft Exchange Server Remote Code Execution Vulnerability"
}
},
"cveMetadata": {
"assignerOrgId": "f38d906d-7342-40ea-92c1-6c4a2c6478c8",
"assignerShortName": "microsoft",
"cveId": "CVE-2023-21529",
"datePublished": "2023-02-14T19:33:00.590Z",
"dateReserved": "2022-12-01T14:00:11.197Z",
"dateUpdated": "2026-08-19T16:26:33.854Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}04 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-04",
"epss": 0.59294,
"percentile": 0.99122
}03 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-03",
"epss": 0.59294,
"percentile": 0.9912
}03 Nov 2026, 02:22 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-02",
"epss": 0.59294,
"percentile": 0.99119
}03 Nov 2026, 02:22 Jerusalem · CISA KEV status changed
Stored KEV snapshot at this observation.
{
"cveID": "CVE-2023-21529",
"cwes": [
"CWE-502"
],
"dateAdded": "2026-04-13",
"dueDate": "2026-04-27",
"forensicTriage": "No",
"knownRansomwareCampaignUse": "Known",
"notes": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529 ; https://nvd.nist.gov/vuln/detail/CVE-2023-21529",
"product": "Exchange Server",
"requiredAction": "Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.",
"shortDescription": "Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.",
"vendorProject": "Microsoft",
"vulnerabilityName": "Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability"
}