CVE-2026-45659

Tenable Blog · Jul 16, 2026

Four Microsoft SharePoint Server vulnerabilities are under active exploitation, prompting CISA to issue a hardening alert. An additional high-severity flaw recently patched adds pressure for organizations running on-premises deployments.Key TakeawaysCISA confirmed active exploitation of three on-premises SharePoint Server vulnerabilities (CVE-2026-32201, CVE-2026-45659, CVE-2026-56164), used to gain unauthorized access, establish remote code execution, steal IIS machine keys and deploy malware for persistence.Two additional SharePoint Server vulnerabilities disclosed on July 14, 2026, CVE-2026-55040 and CVE-2026-58644, were not yet observed exploited at the time of publication, but Microsoft has flagged CVE-2026-58644 as exploited on July 15.Microsoft released patches for all five vulnerabilities and Microsoft Defender Antivirus detection signatures are available to identify exploitation activity for three of the actively exploited flaws.BackgroundTenable's Research Special Operations (RSO) team has compiled this blog to answer Frequently Asked Questions (FAQ) regarding active exploitation of Microsoft SharePoint Server vulnerabilities.FAQWhen did CISA issue an alert about SharePoint Server exploitation?On July 14, 2026, the U.S. Cybersecurity and Infrastructure Security Agency (CISA) published an alert confirming active exploitation of three on-premises SharePoint Server vulnerabilities: CVE-2026-32201, CVE-2026-45659, and CVE-2026-56164. The alert noted that these flaws had been used to gain unauthorized access to SharePoint deployments across all supported on-premises versions and flagged two additional high-risk vulnerabilities, CVE-2026-55040 and CVE-2026-58644, as not yet exploited but warranting immediate patching. However in an update to the security advisory on July 15, Microsoft confirmed CVE-2026-58644 has been exploited in the wild.What vulnerabilities are covered in this alert?Five Microsoft SharePoint Server vulnerabilities are covered in CISA’s...

Daily CyberSecurity · Jul 15, 2026

TL;DR CISA has confirmed active exploitation of three SharePoint vulnerabilities: CVE-2026-32201, CVE-2026-45659, and CVE-2026-56164. Threat actors chain them The post CISA Warns Three SharePoint Server Vulnerabilities Are Exploited in the Wild, Urges Hardening appeared first on Daily CyberSecurity.

All CISA Advisories · Jul 14, 2026

CISA is aware of active exploitation of vulnerabilities CVE-2026-32201, CVE-2026-45659, and CVE-2026-56164, enabling cyber threat actors to gain unauthorized access to on-premises SharePoint Server instances. These vulnerabilities affect all supported on-premises SharePoint Server versions (Subscription Edition, 2019, and 2016) and involve establishing remote code execution (RCE) and post-exploitation activities, such as stealing Internet Information Services (IIS) machine keys and performing deserialization techniques, to gain persistence and deploy malware. Organizations should monitor affected SharePoint Servers closely for any signs of exploitation or unusual activity.  Additionally, the following newly disclosed CVEs are not yet known to have been exploited, but Microsoft has identified them as posing a potential risk if left unpatched: CVE-2026-55040 CVE-2026-58644 CISA urges organizations to detect and remediate a potential compromise by implementing the following recommendations: Apply the latest patches and security updates from Microsoft, verify that installation completes successfully, and shorten patching cycles when possible. Verify that Antimalware Scan Interface (AMSI) integration is enabled for each SharePoint web application. Follow Microsoft’s Configure AMSI integration with SharePoint Server guidance to ensure proper configuration and select the “Full Mode” option for the Request Body Scan Mode, where feasible. When compromise is expected, use the following AMSI and Microsoft Defender Antivirus (MDAV) detections, and implement your organization’s incident response plan for any positive detections: AMSI: Exploit:Script/SuspSignoutReqBody.A – request body scanning; SharePoint Server Subscription only; Microsoft has blocked observed attempts. AMSI: Exploit:Script/ToolPaneAuthBypass.A – request header scanning; SharePoint Server 2016, 2019, and Subscription Edition. AMSI: Exploit:Script/ToolPaneAuthBypass.C – RCE coverage; SharePoint Server...

TheHackerNews · Jul 02, 2026

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) on Wednesday added a high-severity flaw impacting Microsoft SharePoint Server to its Known Exploited Vulnerabilities (KEV) catalog, citing evidence of active exploitation. The vulnerability, tracked as CVE-2026-45659 (CVSS score: 8.8), is a case of remote code execution arising from the deserialization of untrusted data. The issue

All CISA Advisories · Jul 01, 2026

CISA has added one new vulnerability to its Known Exploited Vulnerabilities (KEV) Catalog, based on evidence of active exploitation. CVE-2026-45659 Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability This type of vulnerability is a frequent attack vector for malicious cyber actors and poses significant risks to the federal enterprise. Binding Operational Directive (BOD) 26-04: Prioritizing Security Updates Based on Risk establishes vulnerability management requirements for Federal Civilian Executive Branch (FCEB) agencies. BOD 26-04 reinforces the importance of the KEV Catalog and requires federal agencies to prioritize rapid remediation of high-risk vulnerabilities, specifically those identified by Common Vulnerabilities and Exposures (CVEs) listed in CISA’s KEV Catalog on publicly exposed assets that grant total control of the asset post-exploitation, while deferring action for lower-risk vulnerabilities. BOD 26-04 further establishes basic expectations for when agencies must check whether threat actors compromised the system before the patch was applied. While BOD 26-04 applies only to FCEB agencies, CISA encourages all organizations to adopt risk-based vulnerability management and prioritize remediation of KEV Catalog vulnerabilities. CISA will continue to add vulnerabilities to the catalog that meet the specified criteria. Aware of an exploited vulnerability not currently listed in the KEV Catalog? Submit it for potential addition through CISA’s KEV Nomination Form. Potential KEV additions must have a CVE ID, evidence of exploitation, and clear mitigation guidance. 

TheHackerNews · May 26, 2026

Microsoft has rolled out updates to fix a remote code execution vulnerability impacting SharePoint that could be exploited by bad actors in attacks without requiring any specialized conditions to be met. The vulnerability, tracked as CVE-2026-45659, carries a CVSS score of 8.8. It has been assigned an important severity. "Deserialization of untrusted data in Microsoft Office SharePoint allows

github · Created 2026-07-07 23:52:15 UTC · 0 stars

CVE-2026-45659 - Microsoft SharePoint Deserialization RCE - PoC & Analysis | CVSS 8.8 | AMN SECURITY

github · Created 2026-06-09 11:16:39 UTC · 0 stars

github · Created 2026-05-27 14:12:48 UTC · 0 stars

CVE-2026-45659 Microsoft SharePoint Server Deserialization RCE.

github · Created 2026-05-27 01:25:03 UTC · 0 stars

CVE-2026-45659 - Draft