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

Affected versions of this package are vulnerable to Directory Traversal via the LanguageInformation handling in Kiota.Builder.Models.LanguageInformation and GenerationConfiguration when it reads x-ms-kiota-info clientClassName and clientNamespaceName values. An attacker can overwrite generated output outside the intended directory and inject attacker-controlled text into the generated client by supplying a crafted OpenAPI description with malicious class or namespace names.

Notes

• When Kiota is run without -c/--class-name, the x-ms-kiota-info-supplied client names are treated as the source of truth for the zero-config generation flow, so the issue is reachable in API descriptions intended to drive client scaffolding rather than only in hand-edited configs.
• The same unsanitized names also flowed through configuration binding for per-language settings, so deployments that load Kiota settings from config files or environment-backed configuration could hit the same path/file-write and declaration-injection behavior without using an OpenAPI extension.

Workarounds

• Use kiota generate -c/--class-name <name> instead of relying on the x-ms-kiota-info clientClassName/clientNamespaceName values from the OpenAPI document; this prevents attacker-controlled names in the description from driving the output path or generated declarations.
• Avoid generating clients from untrusted or tampered OpenAPI descriptions when -c/--class-name is omitted; this blocks the zero-config path where provider-supplied x-ms-kiota-info names are consumed directly.

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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