CVE-2021-26857
HIGH
Deserialization of Untrusted Data (CWE-502)
2021-03-03
secure@microsoft.com
7.8
CVSS 3.1
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CVSS VectorNVD
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
Lifecycle Timeline
4
Analysis Generated
Mar 26, 2026 - 11:19 vuln.today
Added to CISA KEV
Dec 18, 2025 - 02:00 cisa
CISA KEV
Patch released
Dec 18, 2025 - 02:00 nvd
Patch available
CVE Published
Mar 03, 2021 - 00:15 nvd
HIGH 7.8
DescriptionNVD
Microsoft Exchange Server Remote Code Execution Vulnerability
AnalysisAI
Microsoft Exchange Server Unified Messaging service contains a deserialization vulnerability that allows authenticated attackers to execute code as SYSTEM, part of the ProxyLogon exploit chain.
Technical ContextAI
The CWE-502 deserialization flaw in the Unified Messaging service processes untrusted serialized .NET objects. When chained with the ProxyLogon SSRF, an unauthenticated attacker can deliver the malicious payload to the Unified Messaging endpoint for code execution as SYSTEM.
Affected ProductsAI
Microsoft Exchange Server 2013/2016/2019 (with Unified Messaging role)
RemediationAI
Apply Microsoft security updates. Disable Unified Messaging if not required. Monitor for deserialization attack indicators.
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External POC / Exploit Code
Leaving vuln.today
Destination URL
POC code from unknown sources may be malicious, contain backdoors, or be fake.
Always review and test exploit code in a safe, isolated environment (VM/sandbox).
Verify the source reputation and cross-reference with known databases (Exploit-DB, GitHub Security).