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

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-20 · updated 2026-06-17
Weakness: CWE-22

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.

Affected products

mesop-dev mesop: before 1.2.3 — fixed in 1.2.3

How to fix

Upgrade to a fixed version: mesop-dev mesop 1.2.3. Check the vendor advisory for mitigations.

References

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