CISA Adds Exploited SharePoint RCE Zero-Day CVE-2026

CVE-2026-25089 is an OS command injection flaw (CWE-78) in Fortinet FortiSandbox caused by improper neutralization of special elements in OS commands, allowing an unauthenticated attacker to execute unauthorized commands by sending specifically crafted HTTP requests to the product. The flaw is network-exploitable with no privileges or user interaction required (CVSS 3.1 score of 9.8), meaning any reachable instance — hardware/VM appliance, FortiSandbox Cloud, or FortiSandbox PaaS — is exposed to system-level command execution. Successful exploitation carries high impact to confidentiality, integrity, and availability on the sandbox itself and can serve as a foothold into the surrounding network. Organizations running FortiSandbox 5.0.0–5.0.5, 4.4.0–4.4.8, or 4.2 (all versions), as well as FortiSandbox Cloud 5.0.4–5.0.5 and FortiSandbox PaaS 5.0.4–5.0.5, are affected. The vulnerability is being actively exploited in the wild: CISA added it to the KEV catalog on 2026-07-16, EPSS assigns a 76.1% probability of exploitation within 30 days (100th percentile), and news coverage describes FortiSandbox bugs under active attack, though no public proof-of-concept is known.

Do: Upgrade FortiSandbox to a release beyond the affected ranges — newer than 5.0.5, 4.4.8, and 4.2 — and update FortiSandbox Cloud and PaaS beyond 5.0.5, following Fortinet's PSIRT advisory for the exact fixed versions (not specified in this data). Until patched, restrict the FortiSandbox management interface from direct internet exposure and review appliance logs for signs of command-injection exploitation. Organizations subject to CISA's KEV requirements must apply vendor mitigations per BOD 26-04 timelines or discontinue cloud use of the product if mitigations are unavailable.

Microsoft SharePoint Server contains an improper input validation flaw (CWE-20) that can be triggered by an unauthenticated, network-based attacker submitting crafted input to the server. Successful exploitation allows the attacker to perform spoofing over the network, impersonating a trusted user or source within SharePoint; detailed impact mechanics have not been published and no CVSS score or public proof-of-concept is available. Any organization running on-premises Microsoft SharePoint Server is potentially affected, and the available data does not specify affected version ranges. CISA added the vulnerability to the Known Exploited Vulnerabilities catalog on 2026-04-14, indicating evidence of active exploitation, and EPSS assigns a 42.8% probability of exploitation within 30 days (99th percentile). Ransomware association is currently unknown.

Do: Apply Microsoft's security updates for SharePoint Server per the vendor advisory as soon as possible, and identify your SharePoint Server versions and builds since specific affected ranges are not provided here. Given the KEV listing, federal agencies must apply the vendor mitigations, follow applicable BOD 22-01 cloud guidance, or discontinue use by the established deadline. Until patched, limit network exposure of SharePoint servers and review authentication and access logs for signs of impersonation or spoofing activity.

CVE-2026-39808 is an OS command injection flaw (CWE-78) in Fortinet FortiSandbox versions 4.4.0 through 4.4.8, caused by improper neutralization of special elements passed to OS commands. The vulnerability is network-reachable, requires no privileges or user interaction (CVSS 3.1: 9.8, AV:N/AC:L/PR:N/UI:N), though CISA's description does not specify the exact entry point that a remote unauthenticated attacker abuses to trigger it. Successful exploitation lets the attacker execute unauthorized code or commands on the appliance, with high impact to confidentiality, integrity, and availability. Any organization running FortiSandbox 4.4.0-4.4.8 is affected; these sandboxing appliances are typically deployed as add-ons to enterprise FortiGate security estates. The flaw was added to CISA's KEV on 2026-07-16, and press coverage describes critical FortiSandbox bugs coming under active attack, so in-the-wild exploitation should be assumed.

Do: Upgrade all FortiSandbox appliances out of the affected 4.4.0-4.4.8 range to a fixed release per Fortinet's advisory, prioritizing internet-exposed units and complying with the CISA KEV required action (added 2026-07-16) and BOD 26-04 guidance. Until patched, restrict network access to the appliance's management and analysis interfaces and triage for signs of command execution such as unexpected processes or outbound connections. Confirm the specific fixed 4.4.x build in Fortinet's PSIRT advisory before scheduling upgrades.

CVE-2026-45659 is a deserialization-of-untrusted-data vulnerability (CWE-502) in Microsoft SharePoint Server in which an authorized (authenticated, low-privilege) attacker can submit crafted serialized data over the network, with no user interaction required, to execute code on the server. Successful exploitation carries high impact on confidentiality, integrity, and availability within the SharePoint service context, giving attackers a foothold for follow-on activity, and CISA notes that ransomware use is known. Organizations running on-premises Microsoft SharePoint Server are affected; the source data lists no specific version ranges, and the CPE scope (sharepoint server) points to the on-premises product rather than the Microsoft-managed SharePoint Online service. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2026-07-01 after active exploitation, and its EPSS score of 76.1% (100th percentile) indicates a high probability of near-term exploitation. The CVE record lists no public proof-of-concept, though related reporting describes exploitation activity following a public PoC release for a SharePoint authentication bypass.

Do: Apply Microsoft's current security updates for SharePoint Server following vendor instructions, prioritizing internet-facing servers, and comply with CISA BOD 26-04, which requires applying mitigations per vendor guidance (including the cited Forensics Triage Requirements) or discontinuing use of the product if mitigations are unavailable. Because in-the-wild exploitation and ransomware use are confirmed, triage exposed servers for compromise: review IIS/SharePoint logs for unexpected authenticated requests, look for webshells or newly modified files in SharePoint web roots, and check for unusual child processes spawned by the SharePoint application pool. Given related reporting on an authentication-bypass PoC, also verify that any related SharePoint authentication-bypass patches are…

Microsoft SharePoint Server contains a missing authentication for critical function vulnerability (CWE-306) that lets an unauthenticated attacker elevate privileges over a network without valid credentials. The flaw is triggered when the affected SharePoint function is accessed remotely without any authentication check, allowing an attacker to gain higher privileges than intended. Successful exploitation could enable an attacker to take elevated actions within the SharePoint environment, potentially leading to further compromise of the server and its data. All organizations running on-premises Microsoft SharePoint Server are potentially affected, though specific versions have not yet been enumerated by Microsoft or CISA. The vulnerability was added to CISA's Known Exploited Vulnerabilities catalog on 2026-07-14, indicating it is being actively exploited, and its EPSS score of 26.6% (98th percentile) reflects a high near-term exploitation risk.

Do: Apply Microsoft's security updates for SharePoint Server as soon as they are available, and check Microsoft's advisory for the specific affected version ranges once published. In the meantime, restrict network access to SharePoint servers, especially for internet-facing instances, and verify whether your environment falls under CISA BOD 26-04 requirements given the KEV listing. Monitor for updated guidance from Microsoft and CISA, as exploitation is confirmed and patching urgency is high.

CVE-2026-58644 is a critical (CVSS 9.8) deserialization-of-untrusted-data flaw (CWE-502) in Microsoft SharePoint Server that allows an unauthorized attacker to execute code over a network. An attacker triggers it by sending crafted serialized data to the server, with no privileges or user interaction required, gaining code execution in the context of the SharePoint service. Any organization running on-premises SharePoint Server is affected, with highest risk for instances reachable from the internet or by untrusted network users. CISA added the flaw to its Known Exploited Vulnerabilities catalog on 2026-07-16, and contemporaneous headlines describe an exploited SharePoint zero-day, indicating active in-the-wild exploitation; EPSS assigns a roughly 16% probability of exploitation within 30 days (97th percentile). Fixes shipped in Microsoft's July 2026 Patch Tuesday release (621 CVEs total), while no public proof-of-concept for this specific CVE is documented.

Do: Apply Microsoft's July 2026 Patch Tuesday security updates for SharePoint Server immediately, prioritizing internet-facing instances, as required for federal agencies under CISA BOD 26-04 and the KEV listing. If patching must be delayed, restrict network exposure to SharePoint per Microsoft/CISA mitigation guidance and assess each asset's internet exposure. Review SharePoint and web-server logs for signs of exploitation and enumerate all SharePoint Server installations in the environment to confirm coverage.