CVE-2026-70259 Overview
CVE-2026-70259 is a Server-Side Request Forgery (SSRF) vulnerability in Microsoft Office SharePoint that allows an authenticated attacker to disclose information over a network. The flaw is tracked under CWE-918 and affects Microsoft SharePoint Server subscription edition.
An attacker with low privileges on a vulnerable SharePoint instance can coerce the server into issuing arbitrary outbound requests. These requests can reach internal services or metadata endpoints that are not directly reachable from the public network, exposing sensitive information.
Critical Impact
An authenticated attacker can abuse SharePoint to make server-side requests to internal resources, resulting in disclosure of confidential data from otherwise inaccessible network segments.
Affected Products
- Microsoft SharePoint Server (Subscription Edition)
- Deployments exposing SharePoint endpoints that accept user-controlled URLs
- On-premises SharePoint farms integrated with internal services or cloud metadata APIs
Discovery Timeline
- 2026-10-13 - CVE-2026-70259 published to the National Vulnerability Database (NVD)
- 2026-10-14 - Last updated in NVD database
- 2026-10-13 - Microsoft Security Response Center (MSRC) advisory published
Technical Details for CVE-2026-70259
Vulnerability Analysis
The vulnerability is a Server-Side Request Forgery (SSRF) classified under CWE-918. SharePoint processes user-supplied input that references a URL or network resource and issues an HTTP request on the server's behalf without sufficient validation of the destination.
Because the request originates from the SharePoint server, it can reach resources that trust the server's network position. These include internal management interfaces, intranet applications, and cloud instance metadata services. The impact is scoped to confidentiality; the attacker reads data returned to the SharePoint process but does not directly modify server state.
Exploitation requires network access to a SharePoint endpoint and valid, low-privileged credentials. No user interaction is required, which makes the issue practical in environments where self-service account registration or broad SharePoint access is enabled.
Root Cause
The root cause is improper validation of a URL or host parameter used in a server-side fetch. SharePoint does not sufficiently restrict the destination scheme, host, or address range before dispatching the outbound request. As a result, loopback addresses, private IP ranges, and cloud metadata endpoints remain reachable.
Attack Vector
The attack vector is network-based. An authenticated attacker submits a crafted request to a SharePoint feature that accepts a URL as input. SharePoint retrieves the attacker-specified resource and returns, reflects, or logs portions of the response. The attacker uses this behavior to enumerate internal services and extract information from them.
No verified proof-of-concept exploit is publicly available at this time. Refer to the Microsoft CVE-2026-70259 Advisory for vendor-supplied technical details.
Detection Methods for CVE-2026-70259
Indicators of Compromise
- Outbound HTTP or HTTPS connections from SharePoint worker processes (w3wp.exe) to internal IP ranges, loopback addresses, or cloud metadata endpoints such as 169.254.169.254.
- SharePoint ULS logs showing unusual URL parameters pointing to private hosts or non-standard ports.
- Spikes in authenticated requests from a single low-privileged account targeting SharePoint features that fetch remote content.
Detection Strategies
- Inspect IIS and SharePoint ULS logs for request parameters containing http://, https://, file://, or gopher:// schemes directed at internal destinations.
- Correlate authenticated SharePoint session activity with outbound connections from the SharePoint host to non-business destinations.
- Baseline normal outbound destinations from SharePoint servers and alert on deviations, particularly connections to link-local or RFC1918 addresses.
Monitoring Recommendations
- Enable egress logging on SharePoint servers and forward logs to a centralized analytics platform for correlation.
- Monitor authentication events for accounts that recently used SharePoint features accepting URL input.
- Alert on any SharePoint-originated traffic to cloud instance metadata services in Azure, AWS, or GCP hosted environments.
How to Mitigate CVE-2026-70259
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft CVE-2026-70259 Advisory to all SharePoint Server subscription-edition farms.
- Audit SharePoint accounts and remove unnecessary low-privileged access, particularly for anonymous or self-registered users.
- Review SharePoint-originated outbound traffic for signs of prior SSRF exploitation.
Patch Information
Microsoft has published guidance and updates through the Microsoft Security Response Center. Administrators should consult the Microsoft CVE-2026-70259 Advisory for the specific build numbers and cumulative updates that remediate the vulnerability on affected SharePoint Server versions.
Workarounds
- Restrict outbound network access from SharePoint servers to only required destinations using host-based or perimeter firewall rules.
- Block SharePoint server access to cloud instance metadata endpoints (for example, 169.254.169.254) when running in cloud environments.
- Place SharePoint servers behind an egress proxy that enforces an allowlist of permitted external destinations.
- Limit which SharePoint features that accept remote URLs are exposed to low-privileged users.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
