CVE-2025-53770

Deserialization of untrusted data in on-premises Microsoft SharePoint Server allows an unauthorized attacker to execute code over a network. Microsoft is aware that an exploit for CVE-2025-53770 exists in the wild. Microsoft is preparing and fully testing a comprehensive update to address this vulnerability. In the meantime, please make sure that the mitigation provided in this CVE documentation is in place so that you are protected from exploitation.

Weakness

The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.

Affected Software

Potential Mitigations

• Make fields transient to protect them from deserialization.
• An attempt to serialize and then deserialize a class containing transient fields will result in NULLs where the transient data should be. This is an excellent way to prevent time, environment-based, or sensitive variables from being carried over and used improperly.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/586.html

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-53770
• https://arstechnica.com/security/2025/07/sharepoint-vulnerability-with-9-8-severity-rating-is-under-exploit-across-the-globe/
• https://github.com/kaizensecurity/CVE-2025-53770
• https://msrc.microsoft.com/blog/2025/07/customer-guidance-for-sharepoint-vulnerability-cve-2025-53770/
• https://news.ycombinator.com/item?id=44629710
• https://research.eye.security/sharepoint-under-siege/
• https://therecord.media/microsoft-sharepoint-zero-day-vulnerability-exploited-globally
• https://www.bleepingcomputer.com/news/microsoft/microsoft-sharepoint-zero-day-exploited-in-rce-attacks-no-patch-available/
• https://www.cisa.gov/news-events/alerts/2025/07/20/microsoft-releases-guidance-exploitation-sharepoint-vulnerability-cve-2025-53770
• https://www.darkreading.com/remote-workforce/microsoft-rushes-emergency-fix-exploited-sharepoint-toolshell-flaw
• https://www.forbes.com/sites/daveywinder/2025/07/20/microsoft-confirms-ongoing-mass-sharepoint-attack---no-patch-available/
• https://x.com/Shadowserver/status/1946900837306868163