EUVD-2026-56414
GHSA-97wg-gxw5-r3h4
Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Network-accessible Exchange endpoint, low complexity, but PR:L required as description specifies an authorized attacker; no confidentiality or integrity impact, only high availability disruption.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Deserialization of untrusted data in Microsoft Exchange Server allows an authorized attacker to deny service over a network.
AnalysisAI
Microsoft Exchange Server's handling of serialized data exposes organizations running Exchange 2016 CU23, Exchange 2019 CU14/CU15, and Exchange Subscription Edition to denial-of-service attacks from low-privileged, network-authenticated users. An authorized attacker exploiting this CWE-502 deserialization flaw can disrupt Exchange availability without requiring elevated permissions, potentially taking down email infrastructure for all dependent users and connected services. Microsoft has released cumulative update patches addressing this vulnerability; no public exploit has been identified at time of analysis.
Technical ContextAI
CWE-502 (Deserialization of Untrusted Data) describes a class of vulnerability where an application deserializes data from an untrusted source without adequate validation, enabling an attacker to supply a maliciously crafted serialized object that triggers unintended behavior during the deserialization process. Microsoft Exchange Server, built heavily on the .NET runtime, processes complex serialized object graphs across mail flow, calendar data, and web service API requests; a crafted payload can cause excessive resource consumption, unhandled exceptions, or process crashes sufficient to produce a high availability impact. Per EUVD-2026-56414, affected builds span Exchange Server 2016 CU23 (build series 15.01.x below 15.01.2507.072), Exchange Server 2019 CU14 (15.02.x below 15.02.1544.044), Exchange Server 2019 CU15 (15.02.x below 15.02.1748.049), and Exchange Server Subscription Edition RTM (15.02.x below 15.02.2562.046).
RemediationAI
Microsoft has released patches for all affected Exchange Server versions. Organizations should upgrade to the following confirmed fix builds: Exchange Server 2016 CU23 to version 15.01.2507.072 or later; Exchange Server 2019 CU14 to version 15.02.1544.044 or later; Exchange Server 2019 CU15 to version 15.02.1748.049 or later; and Exchange Server Subscription Edition to version 15.02.2562.046 or later. Patch guidance is available via the Microsoft Security Response Center at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-62912. Where immediate patching is not operationally feasible, compensating controls include restricting Exchange Web Services and remote PowerShell endpoints to trusted IP ranges only, and ensuring that only the minimum required set of accounts hold Exchange permissions - shrinking the attacker population that can trigger the flaw. Note that restricting EWS may impact third-party integrations, mobile device connectivity, and calendar federation workflows.
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Same weakness CWE-502 – Deserialization of Untrusted Data
View allSame technique Deserialization
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External POC / Exploit Code
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