CVE-2021-42292
Microsoft Excel Security Feature Bypass
Description
CVE-2021-42292 is a high-severity security feature bypass vulnerability in Microsoft Excel that allows local code execution. The flaw enables an attacker to bypass security mechanisms in Microsoft Office products, leading to arbitrary code execution when a user opens a specially crafted Excel file. CISA has added this vulnerability to its Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. With an EPSS score of 19.1% (95.3rd percentile), this Microsoft Excel security feature bypass presents a high probability of exploitation across enterprise environments.
KEV Information
CVSS Score
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | 365 apps | - |
| microsoft | excel | 2013 |
| microsoft | office | 2013; 2016; 2019 |
| microsoft | office long term servicing channel | 2021 |
Multiple CVSS Assessments
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References
Weakness Type
Security Feature Bypass
CVE-2021-42292 involves a security feature bypass in Microsoft Excel where built-in protections that normally prevent macro execution or content loading are circumvented. This allows malicious content embedded in a crafted spreadsheet to execute without triggering the expected security warnings or prompts that users rely on for protection.
Learn more: Security Feature Bypass
Impact Analysis
CVE-2021-42292 carries a CVSS 3.1 score of 7.8 (HIGH), representing a serious threat to organizations using Microsoft Office products. The vulnerability requires local access and user interaction — a victim must open a malicious Excel file — but no authentication is needed to craft and deliver the exploit payload. Once triggered, the impact is severe across all three security dimensions: confidentiality, integrity, and availability are all rated HIGH, meaning an attacker can steal sensitive data, modify files, and disrupt system operations. The EPSS score of 19.1% (95.3rd percentile) places this vulnerability well above the typical exploitation threshold, and its presence in the CISA KEV catalog confirms real-world attacks targeting this flaw.
Exploit Maturity
CVE-2021-42292 is confirmed as actively exploited through its listing in the CISA Known Exploited Vulnerabilities catalog, with a remediation deadline of 2021-12-01. While no publicly available exploit code has been identified in the provided references, the active exploitation status indicates that threat actors have developed and deployed working exploits in targeted campaigns. The EPSS score of 19.1% (95.3rd percentile) confirms a significant exploitation probability. This type of security feature bypass in Microsoft Office is commonly delivered through spear-phishing emails with malicious Excel attachments, making it particularly effective in social engineering campaigns.
Remediation
- Apply Microsoft security updates immediately as required by CISA KEV. Install the November 2021 security updates for all affected Microsoft Office products from the Microsoft Security Response Center advisory.
- Update all affected product versions including Microsoft 365 Apps, Microsoft Excel 2013, Microsoft Office 2013/2016/2019, and Microsoft Office LTSC 2021 to their latest patched releases.
- Implement email filtering and attachment scanning to block or quarantine suspicious Excel files before they reach end users. Configure Microsoft Defender for Office 365 Safe Attachments to detonate files in a sandbox environment.
- Enforce Protected View and Application Guard policies via Group Policy to ensure Excel files from untrusted sources open in a restricted sandbox, limiting the impact of security feature bypass attempts.
- Educate users about the risks of opening unexpected Excel attachments, especially from unknown senders, and establish a reporting mechanism for suspicious emails to enable rapid incident response.
Technical Details
CVE-2021-42292 exploits a security feature bypass in Microsoft Excel that circumvents built-in protections designed to prevent malicious content execution. The vulnerability allows an attacker to craft a specially designed Excel spreadsheet that, when opened by a victim, bypasses security features such as Protected View or macro execution warnings. The CVSS vector (CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H) indicates that while the attack requires local file access and user interaction (opening the file), no privileges are needed and the attack complexity is low. The scope remains unchanged, meaning the impact is confined to the vulnerable application context, but with HIGH ratings across confidentiality, integrity, and availability, the attacker gains significant control over the system once the bypass is triggered.
Frequently Asked Questions
Is CVE-2021-42292 being actively exploited?
Yes. CVE-2021-42292 is listed in the CISA Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. The EPSS score of 19.1% (95.3rd percentile) indicates a high probability of exploitation, and the vulnerability is commonly delivered through malicious Excel attachments.
What products are affected by CVE-2021-42292?
CVE-2021-42292 affects a wide range of Microsoft Office products including Microsoft 365 Apps, Microsoft Excel 2013, Microsoft Office 2013, Microsoft Office 2016, Microsoft Office 2019, and Microsoft Office Long Term Servicing Channel 2021.
How do I fix CVE-2021-42292?
Apply the November 2021 security updates from Microsoft for all affected Office products. Additionally, enforce Protected View policies via Group Policy and implement email filtering to block suspicious Excel attachments before they reach end users.
How severe is CVE-2021-42292?
CVE-2021-42292 has a CVSS 3.1 score of 7.8 (HIGH) and an EPSS score in the 95.3rd percentile. The security feature bypass allows attackers to circumvent Excel's built-in protections, leading to code execution when a victim opens a crafted file.
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