Directory Traversal Affecting mlflow package, versions [0,]

mlflow is a platform to streamline machine learning development, including tracking experiments, packaging code into reproducible runs, and sharing and deploying models.

Affected versions of this package are vulnerable to Directory Traversal via a crafted trace ID submitted to the POST /api/3.0/mlflow/traces endpoint in the FileStore tracking backend. An unauthenticated attacker can supply a trace ID containing traversal sequences that causes FileStore.start_trace() to write trace_info.yaml, request_metadata, and tag files with attacker-controlled metadata to arbitrary filesystem paths outside the intended experiment trace directory, subject to the server process's filesystem permissions. The integrity impact is rated High and availability Low, consistent with the supplied CVSS vectors, reflecting arbitrary file writes with no confidentiality exposure.

Note: This is only exploitable when the FileStore tracking backend is in use. FileStore is the default backend before MLflow 3.7.0 and must be explicitly selected in later versions, where the default changed to a SQLite database.

A Directory Traversal attack (also known as path traversal) aims to access files and directories that are stored outside the intended folder. By manipulating files with "dot-dot-slash (../)" sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration, and other critical system files.

Directory Traversal vulnerabilities can be generally divided into two types:

• Information Disclosure: Allows the attacker to gain information about the folder structure or read the contents of sensitive files on the system.

st is a module for serving static files on web pages, and contains a vulnerability of this type. In our example, we will serve files from the public route.

If an attacker requests the following URL from our server, it will in turn leak the sensitive private key of the root user.

curl http://localhost:8080/public/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/root/.ssh/id_rsa

Note %2e is the URL encoded version of . (dot).

• Writing arbitrary files: Allows the attacker to create or replace existing files. This type of vulnerability is also known as Zip-Slip.

One way to achieve this is by using a malicious zip archive that holds path traversal filenames. When each filename in the zip archive gets concatenated to the target extraction folder, without validation, the final path ends up outside of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.

The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicious file will result in traversing out of the target folder, ending up in /root/.ssh/ overwriting the authorized_keys file:

2018-04-15 22:04:29 .....           19           19  good.txt
2018-04-15 22:04:42 .....           20           20  ../../../../../../root/.ssh/authorized_keys

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