CVE-2020-1493
📋 TL;DR
This CVE describes an information disclosure vulnerability in Microsoft Outlook where files attached as links to emails could be accessed by unauthorized users. Attackers could share email attachments with individuals who shouldn't have access, bypassing organizational security settings. This affects Outlook users who attach files as links rather than embedding them directly.
💻 Affected Systems
- Microsoft Outlook
📦 What is this software?
365 Apps by Microsoft
Office by Microsoft
Outlook by Microsoft
Outlook by Microsoft
Outlook by Microsoft
Outlook by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Sensitive files containing confidential business data, personal information, or credentials could be exposed to unauthorized external parties, leading to data breaches and regulatory violations.
Likely Case
Internal documents or files with limited access permissions could be inadvertently shared with broader audiences than intended, potentially violating data classification policies.
If Mitigated
With proper access controls and monitoring, unauthorized access attempts could be detected and blocked, limiting data exposure.
🎯 Exploit Status
Exploitation requires user interaction (email recipient clicking the link) and some social engineering to convince users to share emails with unauthorized parties.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security updates released in August 2020 - specific version depends on Outlook build
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1493
Restart Required: Yes
Instructions:
1. Open Outlook. 2. Go to File > Office Account > Update Options > Update Now. 3. Install available updates. 4. Restart Outlook when prompted. For enterprise deployments, deploy Microsoft's August 2020 security updates through your patch management system.
🔧 Temporary Workarounds
Disable link attachments
windowsConfigure Outlook to prevent attaching files as links, forcing users to embed files directly
Not applicable - configuration change in Outlook settings
Implement attachment policies
windowsUse Exchange/Office 365 policies to restrict attachment types and sharing permissions
Not applicable - administrative configuration
🧯 If You Can't Patch
- Educate users to avoid attaching files as links and instead embed files directly in emails
- Implement monitoring for unusual file sharing patterns and review access logs for shared file links
🔍 How to Verify
Check if Vulnerable:
Check Outlook version and compare against patched versions in Microsoft's security advisory. Vulnerable if using pre-August 2020 security updates.Check Version:
In Outlook: File > Office Account > About Outlook (shows version number)Verify Fix Applied:
Verify Outlook has August 2020 or later security updates installed and test that file links now respect access permissions.📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns from unexpected IP addresses or user accounts
- Multiple failed access attempts to shared file links
Network Indicators:
- Unexpected external requests to internal file share URLs that were shared via email
SIEM Query:
source="outlook_logs" AND (event="file_link_shared" OR event="attachment_access") AND user NOT IN authorized_users🔗 References
- http://packetstormsecurity.com/files/169960/Microsoft-Outlook-2019-16.0.12624.20424-Out-Of-Bounds-Read.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1493
- http://packetstormsecurity.com/files/169960/Microsoft-Outlook-2019-16.0.12624.20424-Out-Of-Bounds-Read.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1493
