Microsoft Kiota's OpenAPI $ref resolution mechanism in versions before 1.32.5 fetches remote HTTP(S) URLs and reads local files, including absolute and out-of-tree paths, inlining their schemas into the generated client. This behavior enables server-side request forgery (SSRF), remote file inclusion (RFI), and local file inclusion (LFI) during the build process when processing attacker-controlled or influenced OpenAPI specifications. Although the output is escaped to prevent code injection or remote code execution, the side effects include unauthorized outbound requests from the build environment and disclosure of local files not accessible to the attacker. The vulnerability is addressed by introducing a default-deny external reference loader and an explicit allow-list mechanism via the --allowed-external-origins parameter in Kiota versions 1.29.1 and 1.32.5 and later.

The vulnerability allows attackers to induce SSRF from the build or CI host, disclose arbitrary local files through path traversal, and include untrusted remote content in the generated client code. While no remote code execution is possible, the side effects can expose sensitive internal resources and data from the build environment. This can lead to leakage of confidential information and unintended network requests from trusted environments.

Upgrade to Microsoft Kiota version 1.29.1, 1.32.5, or later. These versions implement a default-deny policy for external $ref resolution, blocking all remote HTTP(S) URLs and local file paths unless explicitly allow-listed via the new --allowed-external-origins parameter. Only trusted origins and paths should be added to the allow-list. No other mitigation is required as the vulnerability is fully addressed by these updates.