PatchTheCVECVE-2026-55040: Microsoft SharePoint Weak Authentication Vulnerability
CVE-2026-55040 is a critical-severity flaw (CVSS 9.1) affecting sharepoint server, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Why this priority
- Critical severity
- EPSS top 1%: very likely to be exploited
- Exploited in the wild (CISA KEV)
- Public exploit reference
- CISA SSVC: automatable with total technical impact
- Remotely exploitable, no login, no user action
- On your watchlist
A fixed release or distro patch exists.
Risk facts
| CVSS score | 9.1 (Critical) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 69.5% (top 1%) |
| CISA exploited list | Yes, fix due 2026-08-21 |
| Weakness | CWE-1390 |
| Published | 2026-07-14 |
| Last modified | 2026-08-19 |
Last updated 2026-08-19 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Exploited Added to the CISA Known Exploited Vulnerabilities list
- Updated Record last modified
- Deadline CISA due date for US federal agencies to patch
Exact fixes by distribution
Public exploits and detection
Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.
- GitHub PoC: sfewer-r7/CVE-2026-55040 (59 stars)
- GitHub PoC: l0ggg/CVE-2026-55040 (3 stars)
- GitHub PoC: zenzue/CVE-2026-55040 (0 stars)
- Write-up: www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-
- Nuclei scan template: Microsoft SharePoint Server - JWT Authentication Bypass
Advisories and coverage
Research and news
- VulnCheck Blog: Exploiting SharePoint: CVE-2026-55040 and CVE-2026-63520 RCE Chain 2026-08-24
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-55040?
sharepoint server: upgrade to 16.0.19725.20434. Exact commands for each OS are on this page.
Is CVE-2026-55040 being exploited?
Yes. CVE-2026-55040 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.
What does CVE-2026-55040 affect?
CVE-2026-55040 affects sharepoint server. Severity is critical (CVSS 9.1). Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
How urgent is CVE-2026-55040?
Priority 100/100. Critical severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist
Software pages
SharePoint vulnerabilities · Microsoft Office vulnerabilities
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