Directory Traversal Affecting docling-slim package, versions [2.94.0,2.132.0)

docling-slim is a Modular version of the Docling package: SDK and CLI for parsing PDF, DOCX, HTML, and more, to a unified document representation for powering downstream workflows such as gen AI applications.

Affected versions of this package are vulnerable to Directory Traversal via the TectonicEngine class in docling/backend/latex/engines/tectonic.py when processing LaTeX input containing TikZ pictures. When the Tectonic engine is used to render TikZ diagrams, it compiles the TikZ body and document preamble without restricting TeX file primitives (\openin, \openout, \input, \include, etc.) or shell escape (\write18), allowing an attacker who controls the LaTeX input to read or write arbitrary files on the host filesystem, or execute arbitrary shell commands. Prior to the fix, TectonicEngine defaulted to allow_shell_escape=True, enabling \write18 shell command execution, and performed no pre-flight check for path traversal or unsafe TeX primitives referencing files outside the rendering directory.

Note: This is only exploitable when the LaTeX backend is explicitly configured to render TikZ pictures with the Tectonic engine (LatexBackendOptions(tikz_engine="tectonic")). The default configuration (tikz_engine=None) is not affected.

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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