# CVE-2026-33054: Mesop has a Path Traversal utilizing `FileStateSessionBackend` leads to Application Denial of Service and File Write/Deletion

> Attackers can exploit path traversal in Mesop's FileStateSessionBackend to overwrite or delete files, causing denial of service or data modification.

- **Severity:** Critical 10.0 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Mar 2026
- **Updated:** 20 Mar 2026
- **Also known as:** GHSA-8qvf-mr4w-9x2c, PYSEC-2026-411

## What is CVE-2026-33054?

CVE-2026-33054 is a critical path traversal vulnerability in mesop-dev mesop, published on 20 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Mesop is a Python-based UI framework that allows users to build web applications. Versions 1.2.2 and below contain a Path Traversal vulnerability that allows any user supplying an untrusted state_token through the UI stream payload to arbitrarily target files on the disk under the standard file-based runtime backend. This can result in application denial of service (via crash loops when reading non-msgpack target files as configurations), or arbitrary file manipulation. This vulnerability heavily exposes systems hosted utilizing FileStateSessionBackend. Unauthorized malicious actors could interact with arbitrary payloads overwriting or explicitly removing underlying service resources natively outside the application bounds. This issue has been fixed in version 1.2.3.

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

## Which versions are affected by CVE-2026-33054?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mesop` | PyPI | All versions | 1.2.3 |
| `mesop` | PyPI | All versions | 1.2.3 |
| `mesop` | PyPI | All versions | 1.2.3 |

Products: Mesop-Dev Mesop.

## How do I fix CVE-2026-33054?

Upgrade mesop to 1.2.3 or later.

## Is CVE-2026-33054 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33054 exists.

## Other vulnerabilities in mesop-dev mesop

- [CVE-2026-33057](https://insights.sbomify.com/CVE-2026-33057/): Mesop Affected by Unauthenticated Remote Code Execution via Test Suite Route /exec-py (critical 9.8)
- [CVE-2026-34824](https://insights.sbomify.com/CVE-2026-34824/): Mesop: Unbounded Thread Creation in WebSocket Handler Leads to Denial of Service (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33054 and fix it if it is affected.

What it is: CVE-2026-33054 is a critical path traversal vulnerability in mesop-dev mesop, published on 20 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33054 exists.

Affected packages and fixed versions:
- mesop (PyPI): affected all versions; fixed in 1.2.3
- mesop (PyPI): affected all versions; fixed in 1.2.3
- mesop (PyPI): affected all versions; fixed in 1.2.3

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-2026-33054/ (Markdown: https://insights.sbomify.com/CVE-2026-33054/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33054
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33054
- OSV: https://osv.dev/vulnerability/CVE-2026-33054

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33054/
Summaries are generated and may contain mistakes; the official description above is the record.