CVE-2026-55040Microsoft SharePoint Server Security Feature Bypass Vulnerability
- 9.1CriticalCVSS base score
- 69.5%Exploitation in 30 daysEPSS · top 0.6% of all CVEs
- YesKnown exploitedin CISA's KEV since 18 Aug 2026
- 1Public exploitsMetasploit, Nuclei and Exploit-DB
Description
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Exploited in the wild
CISA lists this vulnerability in its Known Exploited Vulnerabilities catalog as Microsoft SharePoint Weak Authentication Vulnerability.
- Added
- 18 Aug 2026
- Fix due (US federal)
- 21 Aug 2026
- Used by ransomware
- Not known
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.
ENISA's EU Vulnerability Database lists it as exploited, from CISA's KEV, since 18 Aug 2026.
Public exploit
An exploit or proof of concept is public: anyone can try it against an unpatched system. The public collections list a Nuclei template for it. A reference of the record is tagged as an exploit. CISA's SSVC rates its exploitation: it is being exploited.
Show the exploits2
Nuclei templates1 template
- Microsoft SharePoint Server - JWT Authentication Bypass (Nuclei template) (opens in a new tab)
javascript/cves/2026/CVE-2026-55040.yamlSeverity critical
References tagged exploit1 reference
Modules, templates and exploits as listed by the Metasploit Framework (BSD-3-Clause), ProjectDiscovery's Nuclei templates (MIT) and the Exploit Database (GPLv2), read once a day. Where the data comes from
Timeline
ID reserved
By microsoft
- 28 days later
· 28 days later
Published
- 35 days later
· 35 days later
Added to CISA KEV
Known exploited in the wild
- 3 months later
· 3 months later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| microsoftCNA (assigner) | 3.1 | Critical9.1 | 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 |
| NVDNVD · Analyzed | 3.1 | Critical9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
- EPSS (exploitation in 30 days)
- 69.5% · top 0.6% of all CVEs (14 Nov 2026)
- CISA SSVC
- Exploitation: active · Automatable: yes · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.1.
Affected products
Microsoft · Microsoft SharePoint Enterprise Server 2016
- affected 16.0.0 – < 16.0.5561.1001
Microsoft · Microsoft SharePoint Server 2019
- affected 16.0.0 – < 16.0.10417.20175
Microsoft · Microsoft SharePoint Server Subscription Edition
- affected 16.0.0 – < 16.0.19725.20434
References
References4
- Microsoft SharePoint Server Security Feature Bypass Vulnerability (opens in a new tab)vendor-advisorypatch
- https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/ (opens in a new tab)technical-description
- https://github.com/sfewer-r7/CVE-2026-55040 (opens in a new tab)exploit
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040 (opens in a new tab)government-resource
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- CISA KEV catalog (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-44211 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-55040)Record last updated .