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CISA updated its Known Exploited Vulnerabilities catalog to mark CVE-2026-45659 in Microsoft SharePoint Server as linked to known ransomware campaign use, escalating concern around a flaw already tracked as actively exploited. The vulnerability is a deserialization of untrusted data issue that can let an authorized or low-privileged attacker execute arbitrary code over the network on unpatched SharePoint servers, and CISA continues to direct organizations to apply Microsoft mitigations under BOD 26-04.
The agency had previously added the bug to the KEV catalog and required Federal Civilian Executive Branch agencies to remediate it within three days, while also urging defenders to verify patch deployment, monitor SharePoint servers for signs of exploitation, shorten patching cycles, and enable AMSI integration and Microsoft Defender Antivirus detections. Reporting cited internet scans showing more than 8,500 exposed SharePoint servers, including more than 200 still unpatched against CVE-2026-45659, underscoring the ongoing exposure as ransomware operators adopt the exploit.
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3 events from the most recent confirmed update back to the earliest known activity.
CISA updated the KEV catalog entry for CVE-2026-45659 to change known ransomware campaign use from "Unknown" to "Known," indicating the SharePoint flaw is associated with ransomware attacks.
CISA added CVE-2026-45659, a Microsoft SharePoint remote code execution vulnerability, to its Known Exploited Vulnerabilities catalog and required Federal Civilian Executive Branch agencies to remediate it within three days.
Microsoft released security updates in May for SharePoint Enterprise Server 2016, SharePoint Server 2019, and SharePoint Server Subscription Edition to address CVE-2026-45659.
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CISA added **`CVE-2026-45659`** to its Known Exploited Vulnerabilities catalog after confirming active attacks against Microsoft SharePoint Server. The high-severity flaw is a **deserialization of untrusted data** issue that lets an authenticated attacker with only **Site Member** permissions execute arbitrary code on vulnerable, internet-exposed servers, with no user interaction required and low attack complexity. Microsoft said the bug is easy to exploit with repeatable success and released fixes in late May after the CVE was initially omitted from its May 2026 security updates. The vulnerability affects **SharePoint Server Subscription Edition**, **SharePoint Server 2019**, **SharePoint Server 2016**, and **SharePoint Enterprise Server 2016**. CISA ordered Federal Civilian Executive Branch agencies to remediate the issue within days under **BOD 26-04**, while internet scanning data cited by Shadowserver shows more than **10,000** SharePoint servers remain exposed online. Separately, Microsoft disclosed a ransomware investigation involving **Storm-2603** and another threat actor operating in the same compromised environment, where the attackers used persistence, remote access tools, privilege escalation, and defense evasion after initial access was likely obtained through **`CVE-2025-11371`** in Gladinet Triofox.
Jul 12, 2026
**CISA** added **CVE-2026-20963**, a **Microsoft SharePoint** deserialization flaw, to its **Known Exploited Vulnerabilities (KEV)** catalog after confirming active exploitation in the wild. The vulnerability allows an **unauthorized remote attacker** to execute arbitrary code over the network by sending crafted serialized data that SharePoint improperly deserializes, creating a **pre-authentication remote code execution** path. Reporting indicates the specific threat actors behind the attacks have not been publicly identified, but the flaw affects a widely deployed enterprise collaboration platform that often stores sensitive internal documents and communications. The KEV entry triggered urgent remediation requirements, including a **March 21, 2026** deadline for **FCEB agencies** under **Binding Operational Directive 22-01**. Additional reporting notes that the same KEV update also included vulnerabilities in **Wing FTP Server** and **Synacor Zimbra Collaboration Suite**, but the SharePoint issue stands out because of its likely value for **initial access brokers** and **ransomware affiliates** seeking enterprise footholds. Organizations using SharePoint should treat internet-exposed systems as high priority for patching and review for signs of compromise given confirmed in-the-wild exploitation.
Jun 29, 2026
CISA added **`CVE-2026-45659`** to its Known Exploited Vulnerabilities catalog after confirming active exploitation of a high-severity remote code execution flaw in on-premises **Microsoft SharePoint Server**. The vulnerability stems from **deserialization of untrusted data** (`CWE-502`) and carries a **CVSS 8.8** score. It affects **SharePoint Enterprise Server 2016**, **SharePoint Server 2019**, and **SharePoint Server Subscription Edition** below patched versions, and can be exploited over the network by an authenticated attacker with low privileges such as **Site Member**, without user interaction. Microsoft issued fixes in its **May 2026** security updates, later clarifying that the CVE had been inadvertently omitted from the initial update list. CISA set a **July 4, 2026** remediation deadline for federal civilian agencies under Binding Operational Directive 22-01, while public reporting said the exact vulnerable SharePoint component, gadget chain, payload delivery method, and any connection to ransomware activity had not yet been disclosed. Security guidance accompanying the KEV listing urged organizations to patch immediately and review exposed SharePoint environments for signs of compromise.
Jul 10, 2026