10

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-33054

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

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.

(GitHub Advisory)

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CVE-2026-33054

CVE-2026-33054:

10

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
mesop	pip	<= 1.2.2	1.2.3

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability described is a path traversal within the FileStateSessionBackend. The advisory points to the _make_file_path function in mesop/server/state_session.py as the source of the vulnerability. To confirm this and identify the exact function signature, I first identified the patched version (1.2.3) and the last vulnerable version (1.2.2) from the advisory. By comparing the git tags for these versions in the mesop-dev/mesop repository, I located the commit that introduced the fix: c6b382f363b73ac32c402a2db3aadc7784f66a5b. The diff in this commit clearly shows changes to the _make_file_path function in mesop/server/state_session.py. The original code return self.base_dir / (self.prefix + token) was removed. This line is the vulnerability, as it combines a base path with an unsanitized user-provided token. The patch adds validation to the token using a regular expression and resolves the path to ensure it remains within the base directory, thus mitigating the path traversal risk. Therefore, the FileStateSessionBackend._make_file_path function is the precise location of the vulnerability.

Vulnerable functions

FileStateSessionBackend._make_file_path

mesop/server/state_session.py

The function `_make_file_path` within the `FileStateSessionBackend` class is vulnerable to path traversal. It constructs a file path by directly concatenating the user-supplied `token` to a base directory without proper sanitization. An attacker can provide a token with path traversal sequences (e.g., `../../`) to read, write, or delete files outside of the intended storage directory, leading to denial of service or arbitrary file manipulation.

Vulnerability Intelligence
Miggo AI

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WAF Protection Rules

WAF Rule

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Reasoning

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