EUVD-2026-44231
GHSA-g26f-g9f2-wqvr
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
File must be opened locally by a user (AV:L, UI:R) with no attacker privileges (PR:N); memory-corruption code execution yields full C:H/I:H/A:H in the user context.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Lifecycle Timeline
2DescriptionCVE.org
Use of uninitialized resource in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
AnalysisAI
Local code execution in Microsoft Office Excel (2016, 2019, LTSC 2021/2024, Microsoft 365 Apps, Office for Mac, and Office Online Server) allows an attacker to run arbitrary code in the context of the current user when a victim opens a maliciously crafted spreadsheet. The flaw stems from use of an uninitialized resource (CWE-908) and carries a CVSS 7.8; it requires user interaction (opening the file) and no prior privileges. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires a victim to open an attacker-crafted Excel file on an affected Office installation, as reflected by UI:R (required user interaction) and AV:L (local file-based vector) in the CVSS vector; the attacker needs no pre-existing privileges (PR:N) on the target. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 vector CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H yields 7.8 (High), driven by high confidentiality, integrity, and availability impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker emails a finance employee a crafted .xlsx spreadsheet disguised as an invoice or report; when the victim opens it and exits Protected View, Excel processes the malformed structure, triggers the uninitialized-resource condition, and executes attacker-supplied code with the victim's privileges. Because the CVSS vector is AV:L with UI:R, the attack hinges on convincing the user to open the file rather than on any network exposure. … |
| Remediation | Apply the Microsoft-released security update as the primary fix: consult the MSRC advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55949 for the exact patched build for each affected SKU (Microsoft 365 Apps, Excel 2016, Office 2019, Office LTSC 2021/2024, Office for Mac, and Office Online Server), since the input confirms a patch is available but does not list specific version numbers. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, deploy the vendor patch to a test environment for all affected Office versions (Excel 2016, 2019, LTSC 2021/2024, Microsoft 365 Apps, and Office for Mac). …
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Same weakness CWE-908 – Use of Uninitialized Resource
View allSame technique Authentication Bypass
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External POC / Exploit Code
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