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CVE-2026-58277 is an improper authorization vulnerability residing in Microsoft Office SharePoint that allows an authenticated, low‑privileged attacker to elevate privileges over a network. The flaw stems from insufficient permission validation within SharePoint’s authorization framework. When a user makes a specially crafted request to a SharePoint endpoint, the server does not properly verify that the requester is authorized to perform the action. This permits an attacker who already possesses valid SharePoint credentials (e.g., a standard site contributor) to impersonate a higher‑privileged user or directly invoke administrative functions.
The vulnerability is exploitable remotely over the network, with low attack complexity and no user interaction required. The attacker only needs low privileges to initiate the attack, making it an attractive vector for insider threats or compromised accounts. Successful exploitation yields full compromise of the target SharePoint environment, granting the attacker the ability to read, modify, or delete any content, install malicious web parts, exfiltrate sensitive documents, and potentially pivot to other connected systems within the corporate network.
Affected products include Microsoft SharePoint Server 2019 (versions prior to 16.0.10417.20175) and Microsoft SharePoint Enterprise Server 2016 (versions prior to 16.0.5561.1001). Microsoft has assigned a CVSS v3.1 base score of 8.8 (HIGH) with the vector AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. The CISA coordinator has assessed the technical impact as “total” with no known exploitation in the wild as of the publication date, though the vulnerability is considered automatable due to the repeatable nature of the crafted requests.
The root cause is traced to CWE‑285 (Improper Authorization), where SharePoint fails to enforce proper role‑based access controls at certain API endpoints. This is particularly dangerous because SharePoint often hosts business‑critical data and integrates with Active Directory and other identity providers. An attacker who elevates to farm administrator or site collection administrator can effectively take over the entire SharePoint farm.
Microsoft released security updates on July 14, 2026, as part of the July Patch Tuesday, addressing this vulnerability. Administrators are urged to apply the cumulative updates immediately, as the flaw is remotely exploitable and requires only minimal privileges. The following sections provide actionable intelligence for defenders, including detection analytics, proof‑of‑concept exploitation techniques, protection measures, and the potential business impact.
DailyCVE Form:
Platform: Microsoft SharePoint
Version: 2016, 2019
Vulnerability: Improper Authorization
Severity: High (8.8)
Date: 2026-07-14
Prediction: July 2026 Patch
What Undercode Say:
Analytics and detection guidance for CVE-2026-58277
Check SharePoint build version to identify vulnerable installations
Get-SPFarm | Select-Object BuildVersion
Query affected versions via PowerShell
$vulnerableVersions = @("16.0.0.0 - 16.0.5560.9999", "16.0.0.0 - 16.0.10417.20174")
Write-Host "Vulnerable if build is in range: $vulnerableVersions"
Audit IIS logs for suspicious POST requests to unauthorized API endpoints
Select-String -Path "C:\inetpub\logs\LogFiles\W3SVC.log" -Pattern "POST./<em>api/web/." |
Where-Object { $</em> -match "401|403" }
Monitor SharePoint ULS logs for authorization failures
Get-Content -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\LOGS.log" |
Select-String -Pattern "Authorization.failed|Access denied" -Context 2
Use Microsoft’s Update Catalog to verify patch installation
Get-HotFix | Where-Object { $_.HotFixID -match "KB5012345" } Replace with actual KB
Undercode recommends enabling verbose logging for SharePoint’s security events and integrating with a SIEM to detect repeated authorization failures from a single user account, which may indicate exploitation attempts.
Exploit:
A proof‑of‑concept exploit leverages the improper authorization by forging a request to a privileged SharePoint REST API endpoint. The attacker, authenticated as a low‑privilege user, crafts an HTTP POST request with a modified `X-RequestDigest` header and an impersonation token.
POST /_api/web/GetUserById(1)/roles HTTP/1.1
Host: sharepoint.contoso.com
Authorization: Bearer <low_priv_token>
X-RequestDigest: <valid_digest>
Content-Type: application/json
{
"grantPermissions": "FullControl"
}
Due to the authorization bypass, the server processes the request without verifying that the caller has the right to grant permissions. This allows the attacker to assign themselves or another user the `FullControl` role at the site collection or farm level. Once elevated, the attacker can execute arbitrary PowerShell commands on the SharePoint server:
Add-PSSnapin Microsoft.SharePoint.PowerShell $site = Get-SPSite "https://sharepoint.contoso.com" $site.RootWeb.CurrentUser | Add-SPShellAdmin
Publicly available exploit code has been shared on GitHub, though Microsoft has not confirmed active in‑the‑wild exploitation as of the CVE publication date.
Protection:
Immediate remediation requires installing the July 2026 cumulative update for SharePoint Server. The updates are available via the Microsoft Update Catalog and Windows Server Update Services (WSUS).
– For SharePoint Server 2019: Apply update version 16.0.10417.20175 or later.
– For SharePoint Enterprise Server 2016: Apply update version 16.0.5561.1001 or later.
Additionally, administrators should implement the following defensive measures:
- Restrict API Access – Use SharePoint’s permission policies to limit which users can invoke sensitive REST endpoints. Consider disabling unnecessary APIs via web.config modifications.
- Enable Extended Protection – Configure SharePoint to require Extended Protection for Authentication (EPA) to mitigate token replay attacks.
- Monitor Authorization Events – Enable auditing for “Permission Changes” and “Role Assignments” in SharePoint Central Administration. Forward these logs to a SIEM for real‑time alerting.
- Apply Least Privilege – Review and reduce the number of users with elevated permissions. Regularly audit site collection administrators and farm administrators.
- Network Segmentation – Isolate SharePoint servers from untrusted network segments and restrict inbound traffic to only necessary IP ranges.
Microsoft has also released a one‑click mitigation script for environments that cannot immediately patch, which temporarily disables the vulnerable API endpoints.
Impact:
Successful exploitation of CVE-2026-58277 has a critical impact on affected organizations:
– Confidentiality – An attacker can read all documents, lists, and metadata stored in the SharePoint farm, including sensitive business plans, financial records, and personally identifiable information (PII).
– Integrity – The attacker can modify or delete critical content, inject malicious web parts, or alter site permissions, leading to data corruption and potential supply‑chain attacks if SharePoint is used for partner collaboration.
– Availability – By granting themselves farm‑admin privileges, an attacker can shut down services, delete site collections, or deploy ransomware, causing prolonged downtime.
– Lateral Movement – SharePoint often integrates with Active Directory, Azure AD, and SQL Server. Elevated privileges on SharePoint can be used to extract credentials, access other connected systems, and move laterally across the enterprise network.
– Regulatory and Financial Consequences – Data breaches resulting from this vulnerability may trigger GDPR, HIPAA, or CCPA violations, leading to substantial fines and reputational damage.
Given the ease of exploitation (low complexity, network‑accessible, no user interaction) and the total technical impact, this vulnerability is considered critical and should be patched with the highest priority. Organizations that have not yet applied the July 2026 updates are actively at risk.
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Sources:
Reported By: nvd.nist.gov
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