On 2026-08-18, CISA added CVE-2026-55040 (Microsoft SharePoint) to its Known Exploited Vulnerabilities (KEV) catalog [2]. The vulnerability is listed in the catalog as "Microsoft SharePoint Weak Authentication Vulnerability" [2]. CISA requires remediation in accordance with the listed vendor mitigation guidance; see the original text in the body for specific requirements [2].
Backfill: this event became public on Aug 18, 2026 and we added it on Nov 10, 2026. It is not a new event.
CISA Adds Microsoft SharePoint Vulnerability CVE-2026-55040 to Known Exploited Vulnerabilities Catalog
1 min read
- Disclosed
- Aug 18, 2026
- Published
- Nov 10, 2026
- Last updated
- Nov 8, 2026
- CVSS basis
- Our assessment
- 69.5%, higher than 99% of CVEs
- Exploitation and patch status
- ExploitedKEV
- Attack vector
- Vulnerability status
- Actor type
- Motivation
On this page
30-second summary
What happened
Who is affected
Industries mainly affected: Government, Cross-industry
What to do nowOur advice
CISA requires remediation in accordance with the listed vendor mitigation guidance; see the original text in the body for specific requirements [2].
Timeline
Technical details
CISA KEV Listing Record
CISA added CVE-2026-55040 (Microsoft SharePoint) to the Known Exploited Vulnerabilities () catalog on 2026-08-18 [2].
Original Technical Description
Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network. [2]
Official Required Action
Apply 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. [2]
Individual Vulnerability Record
The U.S. National Vulnerability Database (NVD) provides an independent vulnerability record and description for CVE-2026-55040 [1].
References
Official / primary3
- [1]
“Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.”
- [2]CISA2026-08-18Accessed 2026-11-07
This site aggregates public information and is not security consulting advice. Test remediation steps before applying.