Microsoft SharePoint Weak Authentication Vulnerability
Microsoft — Microsoft SharePoint Enterprise Server 2016
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
9.1
39.7%
Vector breakdown
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- Published
- Jul 14, 2026
- Modified
- Aug 19, 2026
- Added to KEV
- Aug 18, 2026
- Federal patch due
- Aug 21, 2026
CISA 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.
Weakness classification
Affected packages
Proof-of-concept & exploitation references
5 foundWeaponization
Public repositories whose name or description references CVE-2026-55040, found via a live GitHub search at request time. These are community-sourced signals, not a verified working exploit - cross-check each one before relying on it, and treat higher star counts and recent activity as (weak) corroboration, not proof.
- sfewer-r7/CVE-2026-55040★ 58
Microsoft SharePoint JWT Authentication Bypass (CVE-2026-55040)
updated Aug 27, 2026
- l0ggg/CVE-2026-55040★ 3
Exploit code for CVE-2026-55040, it can create auth header for any validate account.
updated Aug 20, 2026
- maxprog-svg/CVE-2026-55040-Mass-Exploit★ 0
CVE-2026-55040
updated Aug 27, 2026
- zenzue/CVE-2026-55040★ 0
updated Aug 26, 2026
- virologi-info/mssharepoint-scanner★ 0
A scanner for CVE-2026-55040 and CVE-2026-63520, designed to determine whether the server is affected by these two CVEs.
updated Aug 27, 2026
References
Frequently asked questions
What is CVE-2026-55040?
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
How severe is CVE-2026-55040?
CVE-2026-55040 has a CVSS base score of 9.1 out of 10 (CVSS 3.1).
Is CVE-2026-55040 actively exploited in the wild?
Yes. CVE-2026-55040 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added Aug 18, 2026, meaning CISA has confirmed evidence of active exploitation.
What is the EPSS score for CVE-2026-55040?
39.7% - meaning FIRST.org's EPSS model estimates a 39.7% probability this vulnerability will be exploited in the wild within 30 days (99% percentile among all scored CVEs).
Is there exploit tooling available for CVE-2026-55040?
We found 5 public GitHub repositories referencing CVE-2026-55040, though none matched a known Nuclei template or Metasploit module at last check. Review each one before relying on it - see the proof-of-concept section above.
What type of vulnerability is CVE-2026-55040?
CVE-2026-55040 is classified under CWE-1390 (CWE-1390: Weak Authentication).
Cross-checked against
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