---
title: "CVE-2026-33054: Mesop has a Path Traversal utilizing `FileStateSessionBackend` leads to Application Denial of Service and File Write/Deletion"
url: https://erroneo.us/security/cve/CVE-2026-33054/
description: "CVE-2026-33054 (mesop (PyPI)): Mesop is a Python-based UI framework that allows users to build web applications. Versions 1.2.2 and below contain a Path…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-03-20
date_modified: 2026-03-20
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-33054"
kev: false
cvss: 10
epss: 0.00729
license: All rights reserved. Quote with attribution and a link.
---

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

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.7% , percentile 54: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 54% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes mesop (PyPI) <= 1.2.2, fixed in 1.2.3 . Check your lockfile, including transitive dependencies.

## What it is

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 statetoken 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.

## Affected packages

- PyPI `mesop` <= 1.2.2 → fixed: 1.2.3

## Affected products (CVE record)

- mesop-dev mesop: < 1.2.3

## Severity

- GitHub_M CVSS 3.1: 10 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`
- GitHub CVSS 3.1: 10.0 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.73% probability of exploitation activity in the next 30 days; percentile 54.

## Sources

- [GitHub Advisory GHSA-8qvf-mr4w-9x2c](https://github.com/advisories/GHSA-8qvf-mr4w-9x2c)
- [CVE.org record CVE-2026-33054](https://www.cve.org/CVERecord?id=CVE-2026-33054)
- [NVD entry CVE-2026-33054](https://nvd.nist.gov/vuln/detail/CVE-2026-33054)
- [github.com](https://github.com/mesop-dev/mesop/security/advisories/GHSA-8qvf-mr4w-9x2c)
- [github.com](https://github.com/mesop-dev/mesop/commit/c6b382f363b73ac32c402a2db3aadc7784f66a5b)
- [github.com](https://github.com/mesop-dev/mesop/releases/tag/v1.2.3)

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Source page: https://erroneo.us/security/cve/CVE-2026-33054/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt