CVE-2026-58644: Microsoft SharePoint Deserialization of Untrusted Data Vulnerability
Microsoft SharePoint contains a deserialization of untrusted data vulnerability that allows an unauthorized attacker to execute code over a network.
Overview
Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a network.
Vulnerability details
SharePoint deserializes data supplied by external callers as part of its normal request-handling pipeline. CWE-502 (Deserialization of Untrusted Data) arises when an application reconstructs objects from attacker-controlled bytes without first verifying their integrity or type safety. In .NET-based platforms such as SharePoint, deserialization gadget chains can redirect execution flow during object reconstruction, turning what appears to be a data-parsing step into arbitrary code execution before any application-level logic can intervene.
An unauthenticated attacker with network access to a SharePoint instance sends a crafted serialized payload to a reachable SharePoint endpoint. No credentials and no user interaction are required. When SharePoint deserializes the payload, code executes in the context of the SharePoint server process, giving the attacker full control over confidentiality, integrity, and availability of that server. The only precondition is that the SharePoint instance is reachable over the network from the attacker's position.
Severity and impact
Exploitation status
This vulnerability is confirmed as actively exploited in the wild — it is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog.
Detection and monitoring
- Monitor SharePoint Unified Logging Service (ULS) logs and IIS logs for POST requests to SharePoint endpoints that return HTTP 500 errors or trigger unhandled exceptions immediately after receiving large or binary-encoded request bodies, which may indicate a malformed or weaponized deserialization payload.
- Alert on unexpected child processes spawned by the SharePoint application pool worker process (w3wp.exe), such as cmd.exe, powershell.exe, or wscript.exe, which are not part of normal SharePoint operation and indicate post-deserialization code execution.
Remediation
Additional hardening
- Restrict network access to SharePoint services using perimeter controls; block unauthenticated inbound connections from untrusted IP ranges at the firewall or load balancer.
- Run SharePoint application pools under a least-privilege service account, limiting the OS-level impact of any code execution.
- Deploy Web Application Firewall rules to inspect and block requests containing binary serialization markers targeting SharePoint endpoints.
- Enable Windows Defender Credential Guard and application control policies to constrain process spawning from IIS worker processes.
Key dates
References
Frequently asked questions
Does CVE-2026-58644 affect my FedRAMP authorization?
If Microsoft SharePoint runs inside your authorization boundary, yes. CVE-2026-58644 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, which carries a remediation deadline of July 19, 2026. For a FedRAMP-authorized service, an unpatched KEV in your boundary is a finding — one you either remediate or formally document a mitigation for before your assessor and sponsoring agency raise it.
How does Knox help me handle CVE-2026-58644?
Knox doesn't patch your software for you — remediating Microsoft SharePoint is your responsibility under the FedRAMP shared responsibility model. What Knox gives you is the pre-authorized, single-tenant boundary to remediate in, plus continuous compliance monitoring and audit-artifact coverage that help you document the fix for your next assessment. The fix is yours to apply; staying compliant while you apply it isn't something you manage alone.
How does Knox's monitoring help with vulnerabilities like this?
Knox's continuous monitoring, powered by KnoxAI, watches your environment in real time for newly disclosed vulnerabilities and compliance issues. Exposure surfaces as part of ongoing monitoring — not only when an assessor flags it at review time.
How do I get FedRAMP authorized with Knox?
Book a meeting and Knox maps your path — FedRAMP in 90 days for 90% less, without dependency or delay.
What happens if CVE-2026-58644 isn't remediated by July 19, 2026?
It becomes a POA&M item, and a growing POA&M list is what turns a routine continuous-monitoring review into a real conversation with your agency. Meeting the deadline keeps your authorization clean and the agency relationship intact.
What this vulnerability means for your FedRAMP compliance
Because this flaw is in CISA's Known Exploited Vulnerabilities catalog, FedRAMP continuous monitoring puts a hard remediation clock on it. The clock starts on awareness — and missing the deadline can put an Authority to Operate at risk.
FedRAMP remediation deadlines for actively exploited vulnerabilities
FedRAMP ConMon SLAs give cloud providers 30, 90, or 180 days by severity — but KEV-listed flaws carry the tighter CISA deadline shown above. For authorized services, that date is the compliance line that assessors and agency sponsors will check.
How Knox reduces the burden of CVE vulnerabilities
Remediating the flaw is your responsibility under the FedRAMP shared responsibility model — but staying compliant while you fix it isn't something you manage alone. KnoxAI's continuous monitoring surfaces exposure in real time, and Knox keeps your continuous-monitoring evidence and audit artifacts current while you apply the fix. Learn more about the Knox platform.
How to limit your exposure through inherited controls and isolation
Knox's single-tenant architecture gives every customer a dedicated boundary, and 60–80% of FedRAMP controls are inherited from the platform — shrinking the surface you have to patch and prove. See why teams choose Knox.
Ready to achieve FedRAMP authorization in 90 days or less?
Schedule a meeting to discuss scope, parse readiness, and map your company’s accelerated path to FedRAMP authorization.
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