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Microsoft Word CVE-2026-88167

| EUVDEUVD-2026-99731 MEDIUM
Buffer Over-read (CWE-126)
2026-10-13 secure@microsoft.com GHSA-j8w5-3jg3-qvvc
6.5
CVSS 3.1 · Vendor: microsoft
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Craft malicious Word document
  2. Exploit
    Deliver via email or web download
  3. Execution
    Victim opens file triggering out-of-bounds read
  4. Impact
    Disclose adjacent process memory to attacker

Vulnerability Assessment

Weakness
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Buffer over-read prevention
Exploitation Conditions

Exploitation requires the victim to open an attacker-supplied, specially crafted Word document (UI:R) - this is the primary limiting factor and prevents unattended or wormable mass exploitation. No authentication or prior privileges are needed (PR:N), and the flaw is reachable against default Word configurations (no special feature or non-default setting is called out in the description). The attack is confined to information disclosure: it leaks memory contents but does not, on its own, modify data or crash the application (I:N/A:N). Realistic risk is therefore gated by social-engineering success in getting a user to open the document.

Impact

This is a medium-severity (CVSS 6.5) information-disclosure flaw whose real-world priority is moderate at best, and the available signals are internally consistent rather than conflicting. The CVSS vector (AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N) describes a network-delivered, low-complexity, unauthenticated bug that nonetheless REQUIRES user interaction (UI:R) and yields confidentiality impact only (C:H, I:N, A:N) - i.e., memory disclosure, not code execution or tampering. CISA's SSVC framework reinforces the low-urgency reading: Exploitation = none (no observed or public exploitation), Automatable = no (the required user interaction prevents mass/wormable automation), and Technical Impact = partial. There is no CISA KEV listing and no public proof-of-concept in the supplied data, so exploitation status is 'no public exploit identified at time of analysis.' No EPSS score was provided, so probabilistic exploitation likelihood cannot be quantified. Net: this is a credible but not high-priority issue - the ubiquity of Microsoft Office/Word raises the aggregate exposure, but the mandatory user interaction, lack of integrity/availability impact, SSVC 'none/no/partial' rating, and absence of any exploit evidence argue against emergency prioritization. Patch in the next normal cycle.

Exploit ScenarioDerived

An attacker crafts a malicious Word document that triggers an out-of-bounds read when parsed, and delivers it to a victim via email attachment or a web download. When the victim opens the document, Word reads beyond the intended buffer boundary and exposes adjacent process memory, which can leak sensitive data (e.g., memory layout or document/application secrets). No public exploit code is identified at time of analysis, and the attack cannot succeed without the user opening the file (UI:R).

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.9% exploitation probability (EPSS)

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AnalysisAIv1 – Oct 14, 2026

Information disclosure in Microsoft Word allows an unauthenticated attacker to leak memory contents from a victim's machine when the victim opens a specially crafted Word document. The flaw is a buffer over-read (CWE-126) rated CVSS 6.5, with confidentiality impact limited to memory disclosure and no effect on integrity or availability. Exploitation is gated by user interaction (UI:R) - the attacker must convince a victim to open a malicious file - which prevents unattended or wormable mass abuse; no public exploit code has been identified at time of analysis, CISA's SSVC assessment rates exploitation as 'none', and Microsoft has released vendor patches via the MSRC update guide.

RemediationAI

Apply the Microsoft Office security update documented in the MSRC update guide for CVE-2026-88167 (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-88167); vendor-released patch versions include 16.0.14334.20974 for Office LTSC 2021 and 16.0.17932.21056 for Office LTSC 2024, while Microsoft 365 Apps for Enterprise should be updated to the current Channel build listed at https://aka.ms/OfficeSecurityReleases and the Mac clients (Office LTSC for Mac 2021/2024, Office 365 for Mac) should be updated to the version named in the MSRC advisory. Where patching must be sequenced, compensating controls reduce exposure but with trade-offs: keep Protected View and Application Guard for Office enabled for documents originating from the internet or email attachments (side effect: macro-enabled or embedded-object templates from network locations may be blocked until the file is unblocked manually); configure email/web gateways to strip or quarantine .doc, .docx, .rtf and other Word formats from untrusted senders (side effect: legitimate business attachments are delayed or rejected); and restrict or disable the handling of untrusted Office files on high-value endpoints (side effect: reduced user productivity and possible failure of automated document-processing scripts). These are risk mitigations only - they do not correct the underlying over-read, so the Microsoft update remains the primary fix. Until then, user awareness that opening unexpected Word attachments can leak memory contents is the last line of defense, and there is no indication of active exploitation requiring emergency out-of-band action beyond normal patch cycles.

Affected VersionsENISA

Microsoft Office LTSC 2021 16.0.1 <16.0.14334.20974
Microsoft Office LTSC 2024 16.0.0 <16.0.17932.21056
Microsoft 365 Apps for Enterprise 16.0.1 <https://aka.ms/OfficeSecurityReleases
Microsoft Office LTSC for Mac 2021 16.0.1 <publication
Microsoft Office LTSC for Mac 2024 16.0.0 <publication
Microsoft Office 365 for Mac 1.0.0 <publication

Affected Packages

euvd microsoft_office_ltsc_2021 fix: 16.0.14334.20974
euvd microsoft_office_ltsc_2024 fix: 16.0.17932.21056

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 2 packages in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

The root cause is an out-of-bounds read (CWE-126, buffer over-read) in the code that Microsoft Word uses to parse attacker-supplied document content. Instead of a write primitive, the vulnerable code reads past the end of an allocated memory buffer - typically because a length or offset field embedded in the document is not sufficiently bounds-checked - and the adjacent memory contents can be disclosed back to the attacker in the rendered output, error state, or network traffic. Per the CVSS 3.1 vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N, the attack is network-reachable, low complexity, requires no privileges (PR:N) and no user authentication, but does require a user to open the crafted document (UI:R); scope is unchanged and only confidentiality is impacted (C:H, I:N, A:N). No non-default Word feature or configuration is called out, so the flaw is reachable against default installations. The affected code paths span the Windows Word engine and the macOS Word builds, as reflected in the EUVD version list covering Office LTSC 2021/2024, Microsoft 365 Apps for Enterprise, Office LTSC for Mac 2021/2024, and Office 365 for Mac.

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Severity by source

Vendor (microsoft) PRIMARY 6.5 MEDIUM
AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
vuln.today AI 6.5 MEDIUM

Network-delivered crafted document (AV:N, AC:L, PR:N) that only works when the user opens it (UI:R); a buffer over-read discloses memory, so C:H with no integrity or availability impact.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (microsoft).

CVSS VectorVendor: microsoft

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

Lifecycle Timeline

2
Patch available
Oct 13, 2026 - 20:20 EUVD
CVE Published
Oct 13, 2026 - 19:21 cve.org
MEDIUM 6.5

DescriptionCVE.org

Buffer over-read in Microsoft Office Word allows an unauthorized attacker to disclose information over a network.

Threat Intelligence Overview

EPSS Score
0.9%
Top 43% exploitable
Prevalence
Ubiquitous
Microsoft Office/Word is installed on a huge fraction of enterprise and consumer desktops
Vendor Status
Publicly Disclosed:No
Exploited:No
Latest Software Release:Exploitation Less Likely
Data Quality
5 sources
Confidence: Medium

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.9%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
No
Human Impact· derived
Medium
Technical Impact
Partial

Priority Score

33
Low Medium High Critical
KEV: 0
EPSS: +1
CVSS: +32
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

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