Directory Traversal Affecting microsoft.openapi.kiota package, versions [,1.32.5)

Affected versions of this package are vulnerable to Directory Traversal through the OpenApiDocumentDownloadService and KiotaBuilder document-loading path. An attacker can trigger SSRF, remote file inclusion, and local file inclusion by supplying a spec whose $ref points to an attacker-controlled http(s) URL or to an arbitrary local path. When kiota generate processes such a description, it fetches remote content from the build host and reads local files outside the intended tree, then inlines that data into the generated client, exposing internal services and sensitive files to the resulting output.

Notes

• The vulnerable behavior is present in both the primary generator package and the builder package, so downstream build pipelines that invoke either path can trigger the issue.
• Resolution is transitive across nested references, so a spec that only contains a benign top-level document can still reach external http(s) URLs or out-of-tree local paths through deeper $ref chains.

Workarounds

• Run kiota generate only with --allowed-external-origins entries for trusted $ref targets, and leave the list empty for untrusted specs. This prevents Kiota from loading attacker-controlled remote URLs and out-of-tree local files during OpenAPI resolution.
• If you must allow external references, restrict --allowed-external-origins to specific trusted origins or paths rather than broad patterns; this limits the blast radius of SSRF, remote file inclusion, and local file inclusion from malicious $refs.

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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