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Microsoft Outlook CVE-2026-97016

| EUVDEUVD-2026-99799 CRITICAL
Heap-based Buffer Overflow (CWE-122)
2026-10-13 secure@microsoft.com GHSA-cf52-mp5c-rw57
9.8
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 email message
  2. Delivery
    Deliver to target Outlook mailbox
  3. Exploit
    Trigger heap overflow during message parsing
  4. Execution
    Execute arbitrary code in user context
  5. Impact
    Full compromise of host

Vulnerability Assessment

Weakness
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Heap buffer bounds checking
MITRE ATT&CK

1 technique across 1 tactic: Execution

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

Exploitation Conditions

Exploitation requires the target to run an affected Microsoft Office/Outlook build (Microsoft 365 Apps for Enterprise before the patched release, Office LTSC 2024 before 16.0.17932.21056, or Office LTSC 2021 before 16.0.14334.20974) and to receive an attacker-crafted email that Outlook parses. Per the vendor CVSS vector (PR:N/UI:N), no authentication and no explicit user click are required - consistent with Outlook's automatic message rendering/Preview Pane processing being the trigger. Limiting factors: the victim's Outlook must be updated to a vulnerable version and must receive/render the malicious message; applying the available vendor patch fully removes the condition, and disabling automatic preview/rendering would raise the effective interaction requirement.

Impact

This is a genuine high-priority vulnerability, not a high-CVSS/low-real-risk paper tiger. The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N, C:H/I:H/A:H → 9.8) describes the most dangerous possible profile: network-reachable, low-complexity, no privileges, and - per the vendor-assigned vector - no user interaction, yielding full confidentiality, integrity, and availability compromise. The affected product (Microsoft Outlook / Office) is an extremely high-value, near-ubiquitous target historically favored for email-borne exploitation. Tempering this, several exploitation signals are ABSENT from the input: no EPSS score was provided, there is no CISA KEV listing, no POC availability indicator, and no SSVC decision data - so there is NO confirmation of active or imminent exploitation, only the theoretical severity of the flaw. One point warrants vendor verification: the vector asserts UI:N, yet Outlook heap-overflow RCEs are frequently triggered via email parsing/Preview Pane, which Microsoft conventionally rates as UI:N even though an email must still be received and auto-rendered - verify whether default Preview Pane behavior is the trigger. Net: treat as urgent-to-patch due to severity, product footprint, and a vendor patch already being available, while recognizing exploitation itself is currently unproven in the supplied data.

Exploit ScenarioDerived

A remote attacker crafts a malicious email message that, when received and rendered by Outlook (e.g., via the Preview Pane per the UI:N rating), triggers a heap-based buffer overflow in Outlook's message-parsing code and executes attacker-controlled code in the user's context. No authentication or explicit victim click is indicated by the CVSS vector. No public exploit code is identified in the provided intelligence at time of analysis.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 1.0% exploitation probability (EPSS)

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AnalysisAIv1 – Oct 13, 2026

Remote code execution in Microsoft Outlook allows unauthenticated attackers to execute arbitrary code by sending a crafted email that triggers a heap-based buffer overflow when the message is parsed. Affected versions include Microsoft 365 Apps for Enterprise, Office LTSC 2024 before 16.0.17932.21056, and Office LTSC 2021 before 16.0.14334.20974. No public exploit identified at time of analysis, but the vulnerability is high severity (CVSS 9.8) and requires no user interaction per the vendor vector, making it a serious risk for unpatched systems.

RemediationAI

Apply the vendor-released patches: upgrade Microsoft Office LTSC 2024 to version 16.0.17932.21056 or later, and Microsoft Office LTSC 2021 to version 16.0.14334.20974 or later. For Microsoft 365 Apps for Enterprise, ensure the installation is updated to the latest build via the standard update channel (click-to-run updates automatically; see https://aka.ms/OfficeSecurityReleases). As a compensating control, disabling automatic preview or rendering (e.g., turning off the Preview Pane, reading email in plain text) would raise the effective interaction requirement but may impact usability and is not a full substitute for patching. The Microsoft advisory is at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-97016.

Affected VersionsENISA

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

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 vulnerability is a heap-based buffer overflow (CWE-122) in Microsoft Outlook's email parsing engine. When Outlook processes a specially crafted email, it can write beyond the bounds of a heap-allocated buffer, corrupting memory and potentially allowing an attacker to execute arbitrary code in the context of the Outlook process. The CVSS vector (AV:N/AC:L/PR:N/UI:N) indicates that the attack is network-based, low complexity, requires no privileges, and no user interaction, which is consistent with automatic message rendering or Preview Pane processing. Affected builds are identified by the EUVD as Microsoft 365 Apps for Enterprise, Office LTSC 2024 before 16.0.17932.21056, and Office LTSC 2021 before 16.0.14334.20974. The root cause class, CWE-122, highlights improper bounds checking on heap memory during message parsing.

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  • Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (microsoft) PRIMARY 9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
vuln.today AI 9.8 CRITICAL

Network-delivered email parsing flaw needing no privileges; UI:N retained per vendor on the assumption of automatic Preview Pane rendering, yielding full code-execution impact.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/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
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

2
Patch available
Oct 13, 2026 - 20:20 EUVD
CVE Published
Oct 13, 2026 - 19:22 nvd
CRITICAL 9.8

DescriptionCVE.org

Heap-based buffer overflow in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.

Executive ViewAI

Why It Matters

Microsoft Outlook is affected by a critical remote code execution vulnerability (CVE-2026-97016) that can be triggered by a crafted email, putting endpoints and email-dependent business processes at risk. Although no public exploit identified at time of analysis, the severity and potential for broad impact across Microsoft 365 Apps for Enterprise, Office LTSC 2024, and Office LTSC 2021 make timely remediation a leadership priority. Organizations should act to prevent potential unauthorized code execution and data compromise.

Business Impact: Severe
Compensating Controls

Apply vendor patch.

Threat Intelligence Overview

EPSS Score
1.0%
Top 38% exploitable
Prevalence
High
Microsoft Outlook/Office is among the most widely deployed enterprise email clients
Threat Intel
1
1 sources
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 CRITICAL
CISA KEV No
Public POC No
EPSS 1.0%
Patch available Yes
Active threat No
Deciding rule
CRITICAL severity
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
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
Yes
Human Impact
Very High
Technical Impact
Total

Priority Score

50
Low Medium High Critical
KEV: 0
EPSS: +1
CVSS: +49
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.

A heap overflow occurs when a program writes data beyond the bounds of a buffer allocated in the heap memory region.

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