Exploited vulnerabilities / CVE-2026-55040
Confirmed exploited · exploited vulnerability · Microsoft SharePointCVE-2026-55040
Microsoft SharePoint exploited vulnerability, confirmed exploited in the wild.
Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.
| CISA's name for it | Microsoft SharePoint Weak Authentication Vulnerability |
|---|---|
| Vendor and product | Microsoft · SharePoint |
| Type | exploited vulnerability · CWE-1390 |
| Exploited | Confirmed by CISA listed 18 August 2026 |
| Likelihood | one of the most likely to be exploited of every vulnerability tracked |
| Deadline | 21 August 2026 · already passed |
| Used in ransomware | Not reported |
| Advisories | msrc.microsoft.com ↗ · www.cisa.gov ↗ · www.cisa.gov ↗ · nvd.nist.gov ↗ |
Three steps, in this order
Apply the vendor's fix or mitigation; CISA lists only vulnerabilities seen exploited.
If you cannot patch now, restrict network access to the affected product.
Check for signs of compromise since the date it was added to the list.
| CISA's 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. |
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Know before someone else finds it
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CVE-2026-55040 in short
Is CVE-2026-55040 being exploited?
Yes. CISA added CVE-2026-55040 to its Known Exploited Vulnerabilities catalogue on 18 August 2026, which it does only on evidence of exploitation in the wild.
What is the CISA deadline for CVE-2026-55040?
US federal agencies must remediate it by 21 August 2026. Everyone else should treat that date as the latest safe point to patch an internet-facing system.
How likely is CVE-2026-55040 to be exploited in the next 30 days?
FIRST's Exploit Prediction Scoring System gives it 70%, the 99th percentile of every CVE it scores.
How do I fix CVE-2026-55040?
Apply the vendor's fix or mitigation; CISA lists only vulnerabilities seen exploited. If you cannot patch now, restrict network access to the affected product. Check for signs of compromise since the date it was added to the list.
Other Microsoft vulnerabilities being exploited
| CVE | Product | Type | Listed |
|---|---|---|---|
| CVE-2026-124194 | Office | exploited vulnerability | 10 November 2026 |
| CVE-2026-96951 | Windows | command injection | 13 October 2026 |
| CVE-2026-65660 | SharePoint | exploited vulnerability | 25 September 2026 |
| CVE-2026-81963 | Windows | privilege escalation | 8 September 2026 |
| CVE-2026-85880 | Windows | privilege escalation | 8 September 2026 |
| CVE-2019-1068 | SQL Server | remote code execution | 26 August 2026 |
Sources: CISA Known Exploited Vulnerabilities catalogue (released 10 November 2026) and FIRST EPSS. Page compiled automatically by SAK T.L.M, the threat-intelligence tool of SAK T.E.C, on 13 November 2026.