CVE-2021-27059 is a remote code execution vulnerability in Microsoft Office. CISA added it to the Known Exploited Vulnerabilities catalogue on 3 November 2021, which means attackers have used it in real attacks. Microsoft Office contains an unspecified vulnerability that allows for remote code execution.
What This Vulnerability Means in Microsoft Office
CVE-2021-27059 is dangerous because it turns a document-processing product into an execution path. In practical terms, that means a malicious file or content flow can become a foothold for code execution inside the user’s Office environment, which is why remote code execution issues in productivity software are treated as high-impact enterprise exposure.
For readers tracking exploitation history, the key point is that CISA placed the issue in the KEV catalogue, which confirms real-world abuse and raises the urgency of exposure checks, remediation, and compensating controls. Official version and patch details should be taken from the vendor advisory and the CVE Program record and the NIST National Vulnerability Database entry.
Why Remote Code Execution in Office Matters
Remote code execution in a desktop or collaboration suite is not just a crash or denial of service. It can let an attacker run code under the context of the user opening the content, which may expose email, documents, browser sessions, synced files, and other local or network-reachable material.
The risk is amplified because Office is widely used, often trusted implicitly, and commonly receives files from external sources. A successful exploit can therefore become an initial access event, a data access event, or a staging point for further compromise if the host has broad connectivity or privileged access.
How Organisations Assess Exposure
Exposure review starts with knowing where Microsoft Office is installed, which business units still rely on it, and which endpoints regularly open untrusted files. Asset inventory is essential because patching cannot be validated if the organisation does not know which systems are in scope.
Internet exposure is also relevant, but in this case the bigger question is often document ingress, email delivery, shared storage, and user workflow. Organisations should review vendor advisories, internal software inventories, and any exception lists that delay updates or leave specific devices on older build channels.
Remediation, Detection, and Post-Incident Review
Remediation normally means applying the vendor fix as soon as operationally possible and using compensating controls until then. Those controls can include restricting untrusted document sources, tightening attachment handling, limiting macro and script execution where applicable, and isolating high-risk user groups that handle external files.
Detection should focus on unusual child processes, suspicious Office spawning patterns, abnormal network connections after document open, and endpoint telemetry that indicates a document-triggered execution chain. After patching, organisations should review for signs of pre-patch compromise, because exploitation may have already occurred before the vulnerability was fixed.
Where exploitation is confirmed or strongly suspected, rotate any credentials, session material, or service access that may have been exposed on the affected workstation, especially if the user had access to mail, cloud services, or administrative tools.
Risk and Threat Considerations
Office RCE vulnerabilities are attractive to attackers because they combine a trusted file format with executable impact. In many environments, the most dangerous part is not the vulnerable application alone, but the business habit of opening external content from email, shared drives, or collaboration platforms.
Failure mechanism: An attacker delivers a crafted document or related content path that triggers code execution when the target processes it, then uses that foothold to execute payloads, steal data, or stage follow-on activity.
Impact: The result can be endpoint compromise, user-session abuse, lateral movement, document theft, or a broader intrusion if the affected system has access to sensitive applications or networks.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
MITRE ATT&CK addresses the attack and risk surface, while CIS Controls v8, NIST SP 800-53 Rev 5 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| CIS Controls v8 | CIS-7 — Continuous Vulnerability Management | This CVE requires prioritised vulnerability tracking and remediation. |
| Recommendation — Prioritise the Office CVE for remediation and verify closure with authenticated scanning. | ||
| NIST SP 800-53 Rev 5 | SI-2 — Flaw Remediation | Office RCE remediation depends on timely flaw handling and patch verification. |
| SI-3 — Malicious Code Protection | Exploit delivery through documents makes endpoint protection and inspection materially relevant. | |
| Recommendation — Track the flaw to remediation and confirm affected hosts are updated. Apply malicious code protections to inspect and block weaponised Office content. | ||
| MITRE ATT&CK | T1203 — Exploitation for Client Execution | The vulnerability enables code execution when a victim opens or processes content. |
| Recommendation — Map detections to client-execution exploits and hunt for document-triggered payloads. | ||
| NIST CSF 2.0 | PR.IP-12 — Vulnerability Management | The CVE is a governed vulnerability needing prioritisation, patching, and verification. |
| Recommendation — Place the Office CVE into your vulnerability management workflow and track closure. | ||
Practitioner Guidance
Why practitioners should care: Treat this as an endpoint and identity-adjacent exposure problem, not only a software patching issue. The real business risk is the combination of exploitability, user trust, and whatever access the compromised workstation already holds.
What to watch for: Prioritise systems that open external files frequently, sit outside managed patch cadences, or belong to users with elevated access. If those systems also show suspicious process creation or outbound connections after document open, investigate immediately.
Practitioner takeaway: The safest response is to close the exploit path quickly, then assume any pre-patch compromise may have touched user data, sessions, or connected services.