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Critical, CVSS 10.0amended

Mesop has a Path Traversal utilizing FileStateSessionBackend leads to Application Denial of Service and File Write/Deletion

CVE-2026-33054GHSA-8qvf-mr4w-9x2c

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (mesop 1.2.3), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI mesop

    Affected
    <= 1.2.2
    Fixed in
    1.2.3

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
10.0 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
EPSS
  • CVE-2026-33054: 0.73% estimated exploitation activity in the next 30 days; percentile 54.14 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary A Path Traversal vulnerability allows any user (or attacker) 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. Details When the framework is configured to use the disk-based session backend (FileStateSessionBackend), the user's statetoken actively dictates where the runtime session state is physically saved or queried natively on disk. In mesop/server/server.py, specifically the uistream endpoint, the event.statetoken is collected directly from the untrusted incoming protobuf message struct: mesop.protos.uipb2.UserEvent. Because this is unconditionally passed to FileStateSessionBackend.makefilepath(self, token), it evaluates standard path operators (e.g. ../../../). Python's standard library natively resolves OS traversal…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-8qvf-mr4w-9x2c

  2. Revision 2 · amended ·

    Amended from osv record GHSA-8qvf-mr4w-9x2c

  3. Revision 1 · created ·

    Published from ghsa record GHSA-8qvf-mr4w-9x2c

Agent brief

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# Patch Next advisory brief: CVE-2026-33054

Advisory: Mesop has a Path Traversal utilizing `FileStateSessionBackend` leads to Application Denial of Service and File Write/Deletion
IDs: CVE-2026-33054, GHSA-8qvf-mr4w-9x2c
Record: https://patchnext.com/advisories/cve-2026-33054 (revision 3, source checked 26 Oct 2026, 13:37 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 10.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mesop 1.2.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mesop: affected <= 1.2.2; fixed in 1.2.3

## Suggested inspection (read-only)
- `python -m pip show mesop`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on mesop.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-8qvf-mr4w-9x2c (GitHub-reviewed advisory GHSA-8qvf-mr4w-9x2c lists affected ranges: PyPI mesop >=0 <=1.2.2)
- Verified: https://osv.dev/vulnerability/GHSA-8qvf-mr4w-9x2c (OSV record GHSA-8qvf-mr4w-9x2c lists affected ranges: PyPI mesop >=0 <1.2.3 (fixed))

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