CVE-2018-0798: Microsoft Office Memory Corruption Vulnerability

CVE-2018-0798 is a memory corruption vulnerability in Microsoft Office that arises from the way the software handles objects in memory. Successful exploitation can allow an attacker to run code in the context of the current user. It has been noted as usable in combination with CVE-2018-0802, which raises the practical risk for environments that still run unpatched Office clients.

For IT and security teams, this matters because Office is widely deployed on endpoints that process untrusted documents. Remote code execution under the user’s privileges can lead to further access, credential theft, or lateral movement if other controls are weak. Confirm all version and patch details against the vendor advisory before acting.

How it works

The weakness is classified as CWE-787 (out-of-bounds write), a form of memory corruption. In products like Microsoft Office, such flaws typically occur when the application incorrectly manages object data in memory while parsing a file or related content. An attacker who can get a crafted document opened (or previewed, depending on configuration) may corrupt memory in a way that redirects execution flow.

Public detail on exact exploit mechanics for this CVE is limited in the provided record. In general for this class, the goal is remote code execution as the logged-on user rather than as SYSTEM, unless other elevation paths are available. The record states this vulnerability is known to be chained with CVE-2018-0802; defenders should treat multi-CVE document weaponization as a realistic scenario and verify both issues against Microsoft’s guidance. Do not assume specific file formats, triggers, or reliability without confirming in the vendor advisory.

Am I affected? How to find it in your systems

Microsoft Office is commonly installed on Windows workstations, VDI pools, and some servers used for document processing or automation. Inventory every host that has Office or related components (including viewers or compatibility packs if present in your environment).

• Use software inventory (SCCM/ConfigMgr, Intune, vulnerability scanners, or endpoint management agents) to list installed Office editions and build/version information.
• Compare those versions to the fixed builds listed in Microsoft’s advisory for CVE-2018-0798; do not rely on informal version cutoffs.
• Identify systems that open documents from email, web downloads, file shares, or automated ingestion pipelines—these are higher exposure.
• Review whether protected view, Attack Surface Reduction (ASR) rules, or application control are already in place; their absence increases likelihood of successful exploitation if a malicious file is opened.

Telemetry signs of exploitation for memory-corruption Office bugs are often indirect: unexpected child processes from Office applications (WINWORD.EXE, EXCEL.EXE, POWERPNT.EXE, and similar), Office spawning scripting hosts or command interpreters, crashes followed by suspicious network activity, or document open events correlated with later persistence. Confirm detection logic against your EDR documentation and the vendor advisory; the provided facts do not include unique IOCs for this CVE.

How to remediate

Patch first. Apply the Microsoft updates specified for CVE-2018-0798 (and review related guidance for CVE-2018-0802, given the documented chaining). Follow CISA’s required action: apply updates per vendor instructions. Use your standard enterprise deployment ring process, then verify installation via inventory and compliance reporting.

• Prioritize internet-facing and high-churn user endpoints, then shared workstations and document-processing servers.
• After patching, validate that the effective Office build matches the remediated versions in the advisory.
• Hardening for this class: enforce Protected View for files from the internet and unsafe locations; enable Office MoTW handling; turn on relevant ASR rules that block Office from creating executable content or launching child processes where compatible with business needs; run users without local admin rights.
• Keep endpoint detection and response coverage current so post-exploit behavior is visible even if a future similar bug appears.

If you can't patch immediately

Reduce exposure until the vendor update can be deployed everywhere.

• Segment and restrict: limit outbound connectivity from high-risk workstations where feasible; isolate document-processing jump hosts.
• Mail and file controls: block or sandbox high-risk attachments at the gateway; force sandbox detonation for Office documents from external senders.
• Application hardening: disable unnecessary Office features and legacy format support if policy allows; ensure Protected View and restricted permissions modes are on; consider application control (e.g., allowlisting) so Office cannot launch untrusted binaries.
• Virtual patching / WAF: less applicable to thick-client Office bugs than to web apps, but network IPS/EDS signatures and email gateway rules that target known malicious document patterns can add a layer—tune to avoid sole reliance on them.
• Monitoring: alert on Office spawning cmd, powershell, wscript/cscript, mshta, or unusual network connections; increase logging on endpoints that must remain temporarily unpatched.

These measures lower likelihood and impact but do not replace the official update. Schedule patching as soon as operationally possible and confirm completeness against the vendor advisory.

If your data may have been exposed

Actively exploited vulnerabilities of this type can contribute to endpoint compromise and later data theft, even when ransomware use is not documented for this specific CVE. If you suspect successful exploitation, follow your incident response process: isolate hosts, preserve memory and disk evidence, rotate credentials accessible from the affected user context, and hunt for persistence and lateral movement.

As a supplementary check for personal or work email addresses that may appear in known breach datasets, you can run a free exposure scan to see whether those addresses are present in collected breach records and prioritize password resets and monitoring accordingly.