Critical SharePoint RCE CVE-2026-50522 Under Active Exploitation After Public PoC

A third SharePoint Server flaw patched by Microsoft as part of its Patch Tuesday update for July 2026 has come under active exploitation, per watchTowr.

The vulnerability in question is CVE-2026-50522 (CVSS score: 9.8), a critical deserialization of untrusted data in Microsoft Office SharePoint that could allow an unauthorized attacker to execute code over a network. Microsoft credited DEVCORE researcher “splitline” with discovering and reporting the flaw.

“In a network-based attack, an attacker authenticated as at least a Site Owner, could write arbitrary code to inject and execute code remotely on the SharePoint Server,” Redmond said in an advisory released last week.

“The attack vector is Network (AV:N) because this vulnerability is remotely exploitable and can be exploited from the internet. The attack complexity is Low (AC:L) because an attacker does not require significant prior knowledge of the system and can achieve repeatable success with the payload against the vulnerable component.”

The tech giant also tagged CVE-2026-50522 with an exploitability assessment of “Exploitation More Likely.”

In a post shared on LinkedIn, watchTowr said it has detected active exploitation of the shortcoming against on-premises Microsoft SharePoint deployments following the release of a public proof-of-concept (PoC) exploit, allowing attackers to steal machine keys to maintain persistent access.

“Attackers are pulling SharePoint machine keys via a single request,” the security vendor said. “Patching is not enough; defenders should rotate credentials on any assets that may have been exposed.”

Defused Cyber has also disclosed that threat actors are likely exploiting CVE-2026-50522 to deliver a .NET deserialization payload to a SharePoint sign-in endpoint. “The captured requests carry no authentication material, matching 50522’s unauthenticated profile,” it said.

CVE-2026-50522 is the third vulnerability in SharePoint Server after CVE-2026-56164 (CVSS score: 5.3) and CVE-2026-58644 (CVSS score: 9.8) to witness active exploitation efforts, with the latter two weaponized as zero-days prior to them being fixed in July 2026.