EUVD-2026-56747
GHSA-w35v-hpfj-gw86
Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Network vector and low complexity confirmed by deserialization over HTTP; PR:L reflects required authenticated account; full CIA impact from arbitrary code execution on server.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Lifecycle Timeline
3DescriptionCVE.org
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
AnalysisAI
Remote code execution in Microsoft Office SharePoint enables any authenticated low-privileged user to execute arbitrary code on the server by submitting maliciously crafted serialized data over the network. The CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) confirms the attack requires no user interaction, low complexity, and only a standard SharePoint account - making this straightforward to weaponize within any organization whose SharePoint is network-accessible to internal users or external authenticated parties. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires a valid, low-privileged SharePoint account (PR:L per CVSS vector) and network access to the SharePoint server. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 8.8 High score is well-supported by the vector metrics: network-accessible (AV:N), low attack complexity (AC:L), low privilege (PR:L), no user interaction (UI:N), and full CIA impact (C:H/I:H/A:H). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker with a low-privilege SharePoint account - obtained via phishing, credential stuffing, or insider access - crafts an HTTP request containing a malicious serialized .NET object payload targeting a vulnerable SharePoint endpoint. Upon submission, the SharePoint server deserializes the payload without adequate type validation, executing attacker-controlled code in the IIS application pool context. … |
| Remediation | Apply the Microsoft security update addressing CVE-2026-66805 as released through the MSRC update guide at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66805. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Conduct complete inventory of all SharePoint deployments and low-privilege user accounts with network access; implement firewall rules restricting SharePoint access to essential users only; enable detailed logging of authentication and deserialization events. …
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Same weakness CWE-502 – Deserialization of Untrusted Data
View allSame technique Deserialization
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