Microsoft SharePoint's New RCE Flaw: Patch Now If You Haven't Already
- May 27
- 2 min read
Key Findings
Critical remote code execution vulnerability CVE-2026-45659 identified in Microsoft SharePoint with CVSS score of 8.8
Flaw exploitable by any authenticated user with Site Member permissions or higher, requiring only network access
Root cause is unsafe deserialization of untrusted data allowing arbitrary code execution on servers
Security patches released for SharePoint Server Subscription Edition, SharePoint Server 2019, and SharePoint Enterprise Server 2016
Exploitation requires minimal effort and low-privilege account access, presenting serious risk to unpatched systems
Prior SharePoint vulnerabilities have demonstrated active exploitation patterns in the wild
Background
Microsoft released security updates addressing CVE-2026-45659, a high-severity vulnerability in Microsoft SharePoint that permits remote code execution. The flaw was discovered and reported by a security researcher using the moniker MEOW. This vulnerability sits within a troubling pattern of SharePoint being repeatedly targeted by threat actors over several years, with previous flaws like CVE-2026-32201 documented as actively exploited in real-world attacks.
Technical Details of the Vulnerability
The vulnerability stems from improper handling of serialized data. When SharePoint deserializes untrusted data without adequate validation, attackers can craft malicious payloads that execute arbitrary code on the server. The concerning aspect is the low barrier to exploitation. An attacker needs only an authenticated account with Site Member permissions, the minimum privilege level in SharePoint environments. From there, they can trigger code execution across the network without requiring administrative access or complex preconditions.
Affected Versions and Patch Availability
Organizations running any of the following versions should prioritize immediate patching: SharePoint Server Subscription Edition, SharePoint Server 2019, and SharePoint Enterprise Server 2016. Microsoft has already released updates for all three versions. There is no legitimate reason to delay implementation beyond immediate deployment windows.
Risk Assessment and Historical Context
While Microsoft characterizes this particular flaw as less likely to be exploited compared to other vulnerabilities, this assessment warrants skepticism. SharePoint has an established track record as an attractive target for adversaries. Most notably, CISA added the CVE-2026-32201 SharePoint vulnerability to its Known Exploited Vulnerabilities catalog in April after observing active exploitation. This history strongly suggests CVE-2026-45659 will attract attention from threat actors regardless of Microsoft's initial threat evaluation.
Sources
https://securityaffairs.com/192730/security/microsoft-sharepoint-has-a-new-rce-flaw-if-you-havent-patched-yet-go-do-that.html
https://thehackernews.com/2026/05/microsoft-patches-sharepoint-rce-flaw.html
https://www.develeap.com/news/microsoft-patches-sharepoint-rce-flaw-cve-2026-45659-across-2295a64f
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