CVE-2026-42248: Ollama for Windows Skips Update Signature Checks

CVE-2026-42248 is a missing integrity check in the Windows update routine of Ollama, scored CVSS 9.8 (critical). It accepts downloaded update executables without verifying their signature. Versions 0.12.10 through 0.17.5 are confirmed affected, and no fixed version is stated, so check Ollama's releases.

What's affected

CERT Polska, which coordinated the disclosure, lists Ollama for Windows from 0.12.10 through 0.17.5 as vulnerable. Those versions were tested and confirmed. Other versions were not tested and might also be vulnerable.

The advisory says the maintainers were notified early but did not reply with details of the flaw or the vulnerable version range. I found no fixed version in the record or in the advisory, so I will not name one. Check the Ollama release notes and download page before you decide.

The flaw is specific to the Windows build. The record says the Windows verification routine always reports success, unlike other platforms.

How to check if you're exposed

1. Check the Ollama version in a terminal.

ollama --version

2. If it reads from 0.12.10 through 0.17.5, it is in the tested range. Versions outside that range were not tested, so they may be affected too.
3. Open the Windows Startup folder for each user and look for files you did not put there.

dir "%APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup"

4. Check how Ollama reaches the internet for updates, and whether that traffic crosses a network you do not control.

What to do now

1. List every Windows machine with Ollama installed, including developer laptops and lab systems.
2. Read the Ollama release notes for a version newer than 0.17.5, and check whether it says it fixes update verification. If you cannot confirm that, do not assume it does.
3. Reduce exposure to a tampered update path. Keep the machines on trusted networks, and avoid running updates on public Wi-Fi.
4. If automatic updates cannot be controlled and no fix is confirmed, consider stopping use of Ollama on Windows until a fix is confirmed, or run it in a managed environment that controls its updates.
5. Use application control to allow only signed, approved executables where your organization supports it.
6. Review the related flaw CVE-2026-42249, which chains with this one.

Why it matters

The class is CWE-494, download of code without integrity check. When an application installs an update, the signature is what tells it that the file came from the vendor. If the check always passes, anyone who can alter or replace the download can supply the program that gets run.

The record stresses that Ollama for Windows installs updates silently, so a bad payload could be installed without the user noticing. The CVSS vector is network reachable with no privileges and no user interaction, which is why the score is 9.8. Real exposure depends on whether an attacker can sit in the path of the update request, so the risk is higher on untrusted networks.

CVE-2026-42249 describes a second flaw in the same update path, where values from HTTP response headers are used to build file paths without validation. Together they let a tampered update be written to and run from sensitive locations. Treat the pair as one problem when planning your response.

The KEV flag is false, and I found no report of exploitation in the wild. Many developers run local model tools on laptops that also hold source code and keys, so an unnoticed code execution path there deserves attention even without active attacks. An inventory of tools like this is a practical first step, and the free in-browser dependency scan covers the packages in your own projects.

Quick check

Sources

• CERT Polska advisory for the Ollama update flaws
• Gold page for this CVE

Last reviewed: 19 October 2026.