CVE-2026-55040
What it is
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
At a glance
- Exploitability
- Can be exploited over the network without logging in. High risk of data exposure, data tampering.
- In the wild
- CISA lists this as exploited in real attacks. Treat as urgent.
- Fix
- A patch, advisory or fixed version is referenced. Upgrade or apply it.
Timeline
- ReservedThe CVE id was reserved by its CNA
- PublishedDisclosed publicly on CVE.org and NVD
- 2026-08-18 Exploited in the wildAdded to CISA's Known Exploited Vulnerabilities list
- Last updatedMost recent change to the record
- 2026-08-21 Remediation deadlineCISA's due date for federal agencies to fix it
Why it ranks here
- Exploited in the wild: yes, CISA lists it. This puts it above everything that is not.
- Exploit odds: 69.5% in the next 30 days (EPSS).
- Severity: 9.1 CRITICAL (CVSS).
- Fix: a patch or advisory is linked.
- It meets the bar for Drop everything: critical, and exploited or very likely to be.
Details
- Published
- Last modified
- Added to CISA KEV
- 2026-08-18
- Exploit probability
- 69.5% · EPSS, next 30 days
- Weakness
- CWE-1390
- Record status
- Analyzed
Affected
- Microsoft Sharepoint Server < 16.0.19725.20434
- Microsoft Sharepoint Server 2016
- Microsoft Sharepoint Server 2019
Attack profile CVSS 3.1 · 9.1
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2026-55040.md and follow it. Check whether this project is affected by CVE-2026-55040. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
Fix and advisories
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040
- https://github.com/sfewer-r7/CVE-2026-55040
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040
- https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/