A spoofing vulnerability exists when Office Online Server does not validate origin in cross-origin communications correctly. An attacker could exploit the vulnerability by sending a specially crafted request to an affected site.
The attacker who successfully exploited the vulnerability could then perform cross-origin attacks on affected systems. These attacks could allow the attacker to read content that the attacker is not authorized to read, and use the victim's identity to take actions on the site on behalf of the victim. The victim needs to be authenticated for an attacker to compromise the victim.
The security update addresses the vulnerability by ensuring that Office Online Server properly validates origins.
## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Microsoft | Office Online Server | | [KB4484254](https://patchblox.com/security/data/fix/microsoft/kb4484254.md) | Feb 11, 2020 | --- Data as of 2026-11-07T18:46:35Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.