# CVE-2026-45659: Microsoft SharePoint Server Deserialization of Untrusted Data

> An authorized attacker can execute arbitrary code remotely via unsafe deserialization in Microsoft SharePoint Server.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`)
- **Exploited in the wild:** Yes, since 1 Jul 2026 (CISA KEV), used in ransomware
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 22 May 2026
- **Updated:** 11 Aug 2026
- **Also known as:** GHSA-w3mh-jmwv-56f3

## What is CVE-2026-45659?

CVE-2026-45659 is a high-severity unsafe deserialization vulnerability in Microsoft Sharepoint Server, published on 22 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2026-45659?

It affects 1 product.


Products: Microsoft Sharepoint Server.

## How do I fix CVE-2026-45659?

No fix has been published for CVE-2026-45659 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 4 Jul 2026.

## Is CVE-2026-45659 being exploited?

Yes. Attackers have exploited CVE-2026-45659 in the wild since at least 1 Jul 2026, including in ransomware campaigns.

Public exploit code:

- CVE-2026-45659 (github_poc): https://github.com/HORKimhab/CVE-2026-45659

## 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-2026-45659 and fix it if it is affected.

What it is: CVE-2026-45659 is a high-severity unsafe deserialization vulnerability in Microsoft Sharepoint Server, published on 22 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2026-45659 in the wild since at least 1 Jul 2026, including in ransomware campaigns.

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-2026-45659/ (Markdown: https://insights.sbomify.com/CVE-2026-45659/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45659
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45659
- OSV: https://osv.dev/vulnerability/CVE-2026-45659

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-45659/
Summaries are generated and may contain mistakes; the official description above is the record.