CVE-2026-63518: Microsoft Office Word Remote Code Execution Vulnerability

highCVSS 7.8CVE-2026-63518

Heap-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to execute code locally.

CSIRTS triage

vendor: Microsoft product: Microsoft Office Word Remote code execution Memory corruption

What: Heap-based buffer overflow in Microsoft Office Word allows local code execution.
Who is affected: Systems with Microsoft Office Word installed processing untrusted Word documents.
Urgency: High severity (CVSS 7.8); not exploited but RCE capability requires urgent patching.
Action: Apply the latest Microsoft Office security update.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: high — CVSS 7.8
Published: 2026-08-11
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-63518

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-635180.35% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 28% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-63518	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for Microsoft Office Word

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

mediumCVE-2026-70319: Improper input validation in Microsoft Office Word allows an unauthorized attacker to disclose…nvd · 2026-08-11
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mediumCVE-2026-66810: Heap-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to disclos…nvd · 2026-08-11
mediumCVE-2026-66806: Off-by-one error in Microsoft Office Word allows an unauthorized attacker to disclose informat…nvd · 2026-08-11
mediumCVE-2026-64917: Out-of-bounds read in Microsoft Office Word allows an unauthorized attacker to disclose inform…nvd · 2026-08-11