Summary
Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.
Remediation
CISA required actionApply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
References
- Patchhttps://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040
- Advisoryhttps://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- Advisoryhttps://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
- Advisoryhttps://nvd.nist.gov/vuln/detail/CVE-2026-55040
- Referencehttps://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/
- Referencehttps://github.com/sfewer-r7/CVE-2026-55040
- Referencehttps://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040