CVE-2026-47634: SharePoint Output Injection Spoofing Vulnerability

Technical summary

CVE-2026-47634 is an output encoding failure (CWE-74, CWE-79) in SharePoint that permits improper neutralization of special elements in data passed to downstream rendering components. An authenticated attacker can craft payloads that bypass output encoding, resulting in context-dependent injection. The CVSS 3.1 score of 7.3 (HIGH) reflects network-accessible attack surface, low attack complexity, required authenticated access, user interaction dependency, and high impact to confidentiality and integrity.

Business impact

SharePoint spoofing attacks can undermine trust in internal communications, enable phishing against users who believe they are reading authentic content from trusted sources, facilitate credential harvesting, and potentially spread malware disguised as legitimate internal resources. Given SharePoint's role in document management and team collaboration, successful exploitation could compromise sensitive intellectual property or financial data that appears to come from legitimate internal actors.

Affected systems

Microsoft SharePoint Server is affected. Exact version scope should be verified against the official Microsoft security advisory to determine which product editions and update levels are impacted and whether cloud-hosted (SharePoint Online) or on-premises deployments carry the same risk.

Exploitability

Exploitation requires valid SharePoint user credentials and successful social engineering to trigger user interaction with the malicious content. There is no evidence of active exploitation in the wild (not listed on CISA KEV). However, the low attack complexity and straightforward injection mechanism mean that once discovered, reliable exploits are likely to emerge quickly. The barrier to entry is moderate for insiders but higher for external threat actors.

Remediation

Apply patches from Microsoft as soon as they become available through standard SharePoint update channels. Until patching is complete, restrict SharePoint access to trusted internal users and networks, monitor for unusual content creation or modification patterns, and educate users to verify the source and authenticity of sensitive communications arriving through SharePoint.

Patch guidance

Monitor Microsoft's official security bulletins and the SharePoint product update schedule for patched versions. Prioritize deployment in non-production environments first to validate compatibility. Verify patch applicability for your specific SharePoint edition (Server 2019, 2016, or other variants) before production rollout. Test collaborative workflows and third-party integrations post-patch to ensure no regressions.

Detection guidance

Monitor SharePoint content audit logs for unusual submissions or modifications containing special characters, script tags, or encoded payloads in documents and list items. Flag any rapid creation of content followed by user clicks on suspicious links. Review SharePoint search query logs and click-through patterns for evidence of users accessing spoofed content. Correlate with email gateway logs if SharePoint links are shared externally or in forwarded communications.

Why prioritize this

Although not yet in CISA's KEV catalog, the HIGH severity rating, low attack complexity, and SharePoint's pervasive use in enterprise environments warrant prompt attention. Spoofing attacks are particularly effective in organizations that rely on SharePoint for trusted internal communication. The authentication requirement limits attack surface but not urgency, since insiders and compromised accounts present realistic threats.

Risk score, explained

The 7.3 CVSS score reflects high confidentiality and integrity impact (users can be deceived into disclosing or modifying sensitive information), combined with network accessibility and low attack complexity. The requirement for prior authentication and user interaction prevents a maximum score, but the attack is still reliably exploitable by insiders and creates meaningful risk to data integrity and organizational trust.

Frequently asked questions