CVE-2026-44819: Heap Buffer Overflow in Microsoft Office – Code Execution Risk

Technical summary

CVE-2026-44819 is a heap-based buffer overflow (CWE-122) in Microsoft Office components. The vulnerability exists in memory handling routines that process Office documents. When a malicious document is opened, an attacker can overwrite adjacent heap memory, achieving code execution with user-level privileges. The CVSS v3.1 score of 7.8 (HIGH) reflects the local attack vector (AV:L), low attack complexity (AC:L), no required privileges (PR:N), requirement for user interaction (UI:R), and high impact across confidentiality, integrity, and availability (C:H/I:H/A:H). The vulnerability affects Microsoft 365 Apps, Office 2016 through 2024, and SharePoint Server across multiple editions.

Business impact

Organizations relying on Microsoft Office for daily document handling face elevated risk of data exfiltration, unauthorized file modification, and endpoint compromise. The user-interaction requirement means social engineering or targeted document distribution can trigger exploitation. In enterprise environments with SharePoint Server deployments, compromise could extend to document repositories and collaborative workflows. Remediation delays create a window of vulnerability during which targeted attacks are possible. Supply-chain risks exist if Office documents are shared across trusted partner networks.

Affected systems

The vulnerability affects: Microsoft 365 Apps (all versions exposed), Microsoft Office 2016, 2019, 2021, and 2024 (across multiple editions), and Microsoft SharePoint Server instances. Home users, small businesses, and large enterprises using these widely deployed products are in scope. Organizations with Office document workflows, email-based file sharing, or SharePoint-based collaboration are particularly exposed.

Exploitability

Exploitation requires local file system access and user interaction—the attacker must convince or trick a user into opening a malicious Office document. No network propagation occurs; distribution depends on social engineering, phishing, or supply-chain compromise. The low attack complexity and absence of special privileges mean that once a crafted document reaches a target, the trigger is straightforward. As of the published date, this vulnerability is not yet tracked in CISA's Known Exploited Vulnerabilities catalog, suggesting active exploitation may be limited, but threat actors typically develop exploits for heap overflow vulnerabilities within weeks of disclosure.

Remediation

Microsoft has released security updates addressing this vulnerability across affected Office versions. Organizations should prioritize patching in the following order: (1) systems running Office 2024, 2021, or 365 Apps in high-risk roles (executives, finance, legal, engineering), (2) SharePoint Server installations, (3) Office 2019 and 2016 deployments. Interim mitigations include disabling Office document macros, blocking Office file types at email gateways if not business-critical, and educating users not to open unexpected document attachments. Consider phishing awareness training emphasizing suspicion of unsolicited documents.

Patch guidance

Verify patch availability and version numbers directly from Microsoft's security bulletins corresponding to the published date (June 9, 2026) or later. Patches are typically delivered through Windows Update, Microsoft Update, or Office Update mechanisms. Test patches in a non-production environment before broad deployment to ensure compatibility with line-of-business applications and add-ins. For SharePoint Server, coordinate patching with infrastructure teams to minimize service disruption. Organizations unable to patch immediately should implement enhanced detection and user awareness controls.

Detection guidance

Monitor for unexpected Office process crashes, memory access violations, or heap corruption errors in Windows Event Viewer (Application logs). Endpoint Detection and Response (EDR) solutions should alert on heap spray patterns, unusual Office child process spawning, or file access anomalies following document open. Log suspicious .docx, .xlsx, .pptx, or .doc file handling, especially from external sources. Network detection can focus on Office processes making unexpected outbound connections post-document open. Hunting should prioritize documents received via email or downloaded from untrusted sources in the days following vulnerability disclosure.

Why prioritize this

HIGH severity due to confluence of local code execution capability, high impact (confidential data access, system modification, denial of service potential), and broad affected product base spanning consumer and enterprise Office deployments. While exploitation requires user interaction and local access, the prevalence of Office and email-based document workflows makes this a practical attack vector in targeted campaigns. Organizations with elevated phishing or document-based attack history should elevate priority further.

Risk score, explained

CVSS 7.8 (HIGH) reflects the severity of arbitrary code execution with user-level impact, offset partially by the requirement for local access and user interaction. In a zero-trust security model or environment with strong endpoint controls and user awareness, the practical risk may be lower; in enterprises with lenient document-handling practices or high-value targets, risk approaches CRITICAL. The absence of active exploitation (KEV status: false) does not reduce patch urgency, as heap overflow vulnerabilities are attractive to sophisticated threat actors and proof-of-concept code typically emerges within weeks.

Frequently asked questions