A critical vulnerability, tracked as CVE-2026-45659, in Microsoft SharePoint can allow attackers to achieve remote code execution with little effort.
Microsoft released security updates to patch a high-severity SharePoint vulnerability, tracked as CVE-2026-45659 (CVSS score of 8.8), that could allow remote code execution. The flaw does not require complex conditions for exploitation, making it a serious risk for unpatched systems. Organizations using Microsoft SharePoint should apply the updates as soon as possible.
The root cause is deserialization of untrusted data.
“Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.” reads the advisory. “In a network-based attack, an authenticated attacker, who has a minimum of Site Member permissions (PR:L), could execute code remotely on the SharePoint Server.”
Deserialization of untrusted data is a security vulnerability that happens when an application accepts and processes serialized data from an untrusted source without proper validation. An attacker can craft a payload that runs code on the server. In this case, all it takes is network access and a low-privilege SharePoint account.
The vulnerability was discovered and reported by a researcher using the moniker MEOW. Patches are available for SharePoint Server Subscription Edition, SharePoint Server 2019, and SharePoint Enterprise Server 2016. If you’re running any of these, the update is out and there’s no good reason to wait.
Apply the fix now, not after the next Patch Tuesday retrospective.
Microsoft says exploitation is less likely for this particular flaw, but that assessment deserves some skepticism. SharePoint has a long and well-documented history of being targeted. In April, the U.S. Cybersecurity and Infrastructure Security Agency (CISA) added Microsoft SharePoint Server flaw CVE-2026-32201 to its Known Exploited Vulnerabilities (KEV) catalog.
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