# CVE-2026-45555: Roslyn CodeLens MCP Server: Untrusted Roslyn Analyzer Execution via get_diagnostics Leads to Arbitrary Code Execution

> An attacker can achieve arbitrary code execution by tricking a victim into opening a malicious project with the Roslyn CodeLens MCP Server.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 29 May 2026
- **Updated:** 29 May 2026
- **Also known as:** GHSA-552p-8f74-6x7q

## What is CVE-2026-45555?

CVE-2026-45555 is a high-severity code injection vulnerability in MarcelRoozekrans roslyn-codelens-mcp, published on 29 May 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

Roslyn CodeLens MCP Server is a Roslyn-based MCP server providing semantic code intelligence for .NET codebases. From 0.0.9 to 1.17.0, the get_diagnostics MCP tool loads and executes all DiagnosticAnalyzer assemblies referenced by the target solution without any allowlist, signature check, or user confirmation; includeAnalyzers defaults to true, so no explicit opt-in is required. An attacker who can place a malicious .csproj referencing an attacker-controlled DLL in a location the victim opens with the MCP server will achieve arbitrary code execution in the server process with the server's OS privileges. This vulnerability is fixed in 1.17.0.

Weakness: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-45555?


## How do I fix CVE-2026-45555?

No fix has been published for CVE-2026-45555 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-45555 being exploited?

There is no known exploitation of CVE-2026-45555 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45555 and fix it if it is affected.

What it is: CVE-2026-45555 is a high-severity code injection vulnerability in MarcelRoozekrans roslyn-codelens-mcp, published on 29 May 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-45555 in the wild and no public exploit code.

Affected product: MarcelRoozekrans roslyn-codelens-mcp. 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-2026-45555/ (Markdown: https://insights.sbomify.com/CVE-2026-45555/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45555
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45555
- OSV: https://osv.dev/vulnerability/CVE-2026-45555

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-45555/
Summaries are generated and may contain mistakes; the official description above is the record.