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Fencer Vulns
critical 9.1

CVE-2026-55040 kev in the critical feed json

Microsoft SharePoint Server Security Feature Bypass Vulnerability

published 2026-07-14 3 mo ago modified 2026-11-01 7 d ago also EUVD-2026-44211

cvss
9.1
version 3.1, CNA
cisa kev
Exploited
added 2026-08-18
epss
69.5%
EPSS 69.5% chance of exploitation in 30 days, percentile 99.3%
public exploits
0
none known, plus a Nuclei check

Summary

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

Patch / fix

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.

  • Microsoft Microsoft SharePoint Enterprise Server 2016 16.0.5561.1001
  • Microsoft Microsoft SharePoint Server 2019 16.0.10417.20175
  • Microsoft Microsoft SharePoint Server Subscription Edition 16.0.19725.20434

Timeline

  1. CISA SSVC: exploitation active
  2. Published
  3. Added to CISA KEV
  4. CISA patch deadline

Known exploited

Added
2 mo ago
Patch by
2026-08-21 (2 mo ago)
Ransomware
Not known
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.
Vendor, product
Microsoft, SharePoint
CISA name
Microsoft SharePoint Weak Authentication Vulnerability

CISA SSVC

Exploitation
Active, exploited in the wild
Automatable
yes
Technical impact
total
Assessed
3 mo ago

Exploit prediction

69.54% chance of exploitation in the next 30 days, higher than 99.3% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • Nuclei template Microsoft SharePoint Server - JWT Authentication Bypass nuclei detection template
  • github.com https://github.com/sfewer-r7/CVE-2026-55040 referenced PoC, tagged "exploit" by a source, unverified
  • cisa.gov https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:C
CNA 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

  • Microsoft Microsoft SharePoint Enterprise Server 2016
  • Microsoft Microsoft SharePoint Server 2019
  • Microsoft Microsoft SharePoint Server Subscription Edition

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.