# CVE-2026-55040: Microsoft SharePoint Weak Authentication

> An unauthorized attacker can bypass security features in Microsoft SharePoint Server via weak authentication mechanisms.

- **Severity:** Critical 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`)
- **Exploited in the wild:** Yes, since 18 Aug 2026 (CISA KEV)
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Jul 2026
- **Updated:** 28 Oct 2026
- **Also known as:** GHSA-grxw-7cvc-96rv

## What is CVE-2026-55040?

CVE-2026-55040 is a critical vulnerability in Microsoft Sharepoint Server, published on 14 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

Weakness: CWE-1390 (Weak Authentication)

## Which versions are affected by CVE-2026-55040?

It affects 1 product.


Products: Microsoft Sharepoint Server.

## How do I fix CVE-2026-55040?

No fix has been published for CVE-2026-55040 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 21 Aug 2026.

## Is CVE-2026-55040 being exploited?

Yes. Attackers have exploited CVE-2026-55040 in the wild since at least 18 Aug 2026.

Public exploit code:

- Microsoft SharePoint JWT Authentication Bypass (CVE-2026-55040) (github_poc): https://github.com/sfewer-r7/CVE-2026-55040
- Exploit code for CVE-2026-55040, it can create auth header for any validate account. (github_poc): https://github.com/l0ggg/CVE-2026-55040
- https://github.com/zenzue/CVE-2026-55040 (github_poc): https://github.com/zenzue/CVE-2026-55040
- CVE-2026-55040 (github_poc): https://github.com/maxprog-svg/CVE-2026-55040-Mass-Exploit
- A scanner for CVE-2026-55040 and CVE-2026-63520, designed to determine whether the server is affected by these two CVEs. (github_poc): https://github.com/virologi-info/mssharepoint-scanner
- Microsoft SharePoint Server - JWT Authentication Bypass (nuclei)

## Other vulnerabilities in Microsoft Sharepoint Server

- [CVE-2026-50522](https://insights.sbomify.com/CVE-2026-50522/): Microsoft SharePoint Deserialization of Untrusted Data Vulnerability (critical 9.8, exploited in the wild)
- [CVE-2026-58644](https://insights.sbomify.com/CVE-2026-58644/): Microsoft SharePoint Deserialization of Untrusted Data (critical 9.8, exploited in the wild)
- [CVE-2026-20963](https://insights.sbomify.com/CVE-2026-20963/): Microsoft SharePoint Deserialization of Untrusted Data (critical 9.8, exploited in the wild)
- [CVE-2025-53770](https://insights.sbomify.com/CVE-2025-53770/): Microsoft SharePoint Deserialization of Untrusted Data (critical 9.8, exploited in the wild)
- [CVE-2023-29357](https://insights.sbomify.com/CVE-2023-29357/): Microsoft SharePoint Server Privilege Escalation (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55040 and fix it if it is affected.

What it is: CVE-2026-55040 is a critical vulnerability in Microsoft Sharepoint Server, published on 14 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2026-55040 in the wild since at least 18 Aug 2026.

Affected product: Microsoft Sharepoint Server. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55040/ (Markdown: https://insights.sbomify.com/CVE-2026-55040/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55040
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55040
- OSV: https://osv.dev/vulnerability/CVE-2026-55040

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55040/
Summaries are generated and may contain mistakes; the official description above is the record.