# CVE-2026-21851: MONAI has Path Traversal (Zip Slip) in NGC Private Bundle Download

> Attackers can exploit a path traversal vulnerability in MONAI's private bundle download to write arbitrary files, potentially leading to code execution.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 7 Jan 2026
- **Updated:** 8 Jan 2026
- **Also known as:** GHSA-9rg3-9pvr-6p27, PYSEC-2026-1678

## What is CVE-2026-21851?

CVE-2026-21851 is a medium-severity path traversal vulnerability in Project-MONAI MONAI, published on 7 Jan 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

MONAI (Medical Open Network for AI) is an AI toolkit for health care imaging. In versions up to and including 1.5.1, a Path Traversal (Zip Slip) vulnerability exists in MONAI's `_download_from_ngc_private()` function. The function uses `zipfile.ZipFile.extractall()` without path validation, while other similar download functions in the same codebase properly use the existing `safe_extract_member()` function. Commit 4014c8475626f20f158921ae0cf98ed259ae4d59 fixes this issue.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-21851?

3 open source packages ship an affected version, including monai. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `monai` | PyPI | All versions | 1.5.2 |
| `monai` | PyPI | All versions | 1.5.2 |
| `monai` | PyPI | All versions | 1.5.2 |

Products: Project-Monai Monai.

## How do I fix CVE-2026-21851?

Upgrade monai to 1.5.2 or later.

## Is CVE-2026-21851 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21851 exists.

## Other vulnerabilities in Project-MONAI MONAI

- [CVE-2026-100846](https://insights.sbomify.com/CVE-2026-100846/): MONAI before 1.5.2 Remote Code Execution via Pickle Deserialization (high 8.8)
- [CVE-2026-100844](https://insights.sbomify.com/CVE-2026-100844/): MONAI before 1.6.0 OS Command Injection via dataset_name_or_id (high 8.6)
- [CVE-2026-100840](https://insights.sbomify.com/CVE-2026-100840/): MONAI through 1.6.0 Remote Code Execution via bundle configuration (high 8.5)
- [CVE-2026-100841](https://insights.sbomify.com/CVE-2026-100841/): MONAI through 1.6.0 PersistentDataset Remote Code Execution via Pickle Cache (high 8.5)
- [CVE-2026-100843](https://insights.sbomify.com/CVE-2026-100843/): MONAI before 1.6.0 Remote Code Execution via algo_from_pickle (high 8.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-21851 and fix it if it is affected.

What it is: CVE-2026-21851 is a medium-severity path traversal vulnerability in Project-MONAI MONAI, published on 7 Jan 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21851 exists.

Affected packages and fixed versions:
- monai (PyPI): affected all versions; fixed in 1.5.2
- monai (PyPI): affected all versions; fixed in 1.5.2
- monai (PyPI): affected all versions; fixed in 1.5.2

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-2026-21851/ (Markdown: https://insights.sbomify.com/CVE-2026-21851/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21851
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21851
- OSV: https://osv.dev/vulnerability/CVE-2026-21851

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21851/
Summaries are generated and may contain mistakes; the official description above is the record.