EUVD-2026-43774
GHSA-cjqx-7vg8-mm6c
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Code executes locally only when a user opens a crafted file, so AV:L and UI:R; no attacker privileges (PR:N) and full RCE in user context gives C/I/A:H.
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
Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
AnalysisAI
Local arbitrary code execution in Microsoft Excel arises from a heap-based buffer overflow (CWE-122) triggered when a user opens a maliciously crafted spreadsheet; successful exploitation runs attacker code in the context of the current user across desktop Office builds (Excel 2016, Office 2019, LTSC 2021/2024, Microsoft 365 Apps) on both Windows and Mac, as well as Office Online Server. The flaw carries CVSS 7.8 with high confidentiality, integrity, and availability impact but requires user interaction (opening the file). …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires a victim to open a specially crafted Excel workbook (UI:R in the CVSS vector) - the attacker cannot trigger the overflow without that user action. … 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): the local attack vector combined with required user interaction reflects the classic 'victim opens a malicious file' pattern rather than remote unauthenticated compromise - PR:N means no attacker privileges are needed, but UI:R means an authorized user must be socially engineered into opening the document. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker crafts a malicious Excel workbook whose internal records trigger the heap overflow and emails it as a phishing lure (e.g., a fake invoice or report) to a target user. When the victim opens the file - and, if prompted, dismisses Protected View - the overflow corrupts the heap and executes attacker-controlled code with the user's privileges, giving a foothold for further actions. … |
| Remediation | Patch available per vendor advisory: apply the Microsoft update for CVE-2026-58618 documented at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-58618, which covers Microsoft 365 Apps, Excel 2016, Office 2019, Office LTSC 2021/2024, the Mac builds, and Office Online Server (exact patched build numbers per channel are listed in the MSRC guide and are not reproduced in the input, so verify the target build there rather than assuming a version). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, complete asset inventory identifying all deployed versions of Excel 2016, Office 2019, LTSC 2021/2024, Microsoft 365 Apps, and Office Online Server; simultaneously issue user advisory warning against opening untrusted spreadsheet attachments. …
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Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Heap Overflow
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External POC / Exploit Code
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