Disabling Inline SVG Image Display in Outlook for Web and Windows

Overview

Microsoft has announced a significant security enhancement for Outlook users. As part of this update, inline SVG (Scalable Vector Graphics) image support will be retired across both Outlook for Web (OWA) and the new Outlook for Windows platforms. This change is a proactive measure designed to strengthen email security infrastructure and mitigate potential cybersecurity threats. The phased rollout is set to ensure comprehensive coverage across all Microsoft 365 environments, with a completion timeline designed to minimize disruption and allow organizations ample time to adapt.

Who It Impacts

• Outlook Users: All organizations and users that rely on Outlook for Web or Outlook for Windows.
• Email Senders: Any entity that embeds SVG images directly within the body of their emails (inline SVG).
• Government and Specialized Environments: This update also impacts GCC, GCC-H, DoD, and Gallatin deployments, which will begin seeing this change in mid-September 2025, with full implementation by mid-October 2025.

How It Impacts

• Inline SVG Rendering Disabled: Inline SVG images embedded directly within email content will no longer render in Outlook for Web and Windows. Instead, these will appear as blank spaces or broken image icons.
• Security Vulnerabilities Addressed: The removal of inline SVGs is aimed at addressing critical security concerns, particularly around cross-site scripting (XSS) attacks. SVG files can be used to inject malicious JavaScript code, posing a risk when rendered inline in email clients.
• No Impact on SVG Attachments: While inline SVG images are being retired, SVG attachments will remain fully supported. Users can still send and receive SVG files as attachments, and recipients can download them from the attachment section without issue.
• Minimal Disruption: Microsoft’s data indicates that this change will affect less than 0.1% of all images used in Outlook, ensuring minimal operational disruption while significantly improving security.

Targeted Products

• Outlook for Web (OWA)
• Outlook for Windows (Desktop)
• Microsoft 365 Environments (including GCC, GCC-H, DoD, and Gallatin environments)

Recommendations

1. Update Email Content: Organizations should replace inline SVG images with alternative image formats (PNG, JPEG, GIF) for email signatures, logos, or other embedded content.
2. Review Email Communication Strategies: Ensure that emails no longer rely on inline SVGs for critical content. Update internal documentation and inform users who commonly use SVGs in emails.
3. Monitor Impact: Since the phased rollout is ongoing, it is advised to monitor the impact of this change on email renderings within your organization and communicate any required adjustments.
4. Test Email Compatibility: Test emails containing SVGs to ensure that users are not experiencing broken images and that alternative formats display correctly across different email clients.
5. Stay Informed: Stay updated on further security developments from Microsoft and any additional changes related to email content rendering in Outlook.

References

• https://cybersecuritynews.com/cisa-practices-secure-microsoft-365-cloud/
• https://cybersecuritynews.com/disable-svg-images-display-outlook/
• https://cybersecuritynews.com/hackers-svg-image-files-deliver-guloader-malware/
• https://cybersecuritynews.com/http-2-security-arbitrary-cross-site-scripting/