CVE-2026-55040 Microsoft SharePoint: login or permission bypass
In plain words: A door that should be locked is not: part of the system can be reached without a valid login or permission. The attacker gets in as a user or administrator without knowing a password.
Confirmed exploited by CISA on · US federal patch deadline Aug 21, 2026
What to do
- Install Microsoft's security update for SharePoint. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Keep a list of every internet-facing server you run so nothing is forgotten.
- Patch anything in this catalog first, ahead of normal patch cycles.
- Put admin and file-transfer apps behind a VPN or single sign-on instead of the open internet.
Who is affected
Work IT. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.
What's at risk: Mass data theft and ransomware: a single flaw in a file-transfer or email server has exposed thousands of organisations at once.
The details
- Official name
- Microsoft SharePoint Weak Authentication Vulnerability
- Product
- Microsoft SharePoint
- CISA description
- Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.
- Type of flaw
- Login or permission bypass (CWE-1390)
- Confirmed exploited
- Aug 18, 2026
- US federal patch deadline
- Aug 21, 2026
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Answering about CVE-2026-55040 ·
Questions about CVE-2026-55040
Is CVE-2026-55040 being exploited?
Yes. CISA added CVE-2026-55040 to its Known Exploited Vulnerabilities catalog on Aug 18, 2026, which means there is reliable evidence of real-world attacks.
How do I fix CVE-2026-55040?
Install Microsoft's security update for SharePoint. If no update exists, follow the vendor's workaround or stop using the product until one ships. Keep a list of every internet-facing server you run so nothing is forgotten.
Am I affected by CVE-2026-55040?
Only if you use Microsoft SharePoint. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.