7.1

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-59867

CVE-2026-59867: Microsoft Kiota: Generation-time SSRF + remote/local file inclusion via unrestricted $ref

Summary

Microsoft Kiota resolved OpenAPI $refs by fetching remote http(s) URLs and reading local files (including absolute / out-of-tree paths), inlining the referenced schema into the generated client. Running kiota generate on a spec whose $ref pointed at an attacker/internal URL or an arbitrary local file yielded SSRF, remote file inclusion, and local file inclusion. Verified on 1.32.3 / 1.32.4.

Details

$ref: http://attacker/internal-evil.json#/... → build host fetches the URL (SSRF) and inlines the remote schema (RFI); confirmed property REMOTE_KIOTA_PROP in the generated client.
$ref: /abs/path.json#/... or ../../secret.json#/... → Kiota reads the out-of-tree local file and inlines its schema (LFI); confirmed Leaked schema in the generated client. Resolution is transitive across nesting levels.

Kiota escapes its output sinks (comments/strings/identifiers), so attacker-controlled remote/local content cannot break out into code — no RCE. The chain stops at SSRF + RFI + LFI.

Impact

Build-time SSRF (CWE-918) from the developer or CI host, disclosure of arbitrary local files (CWE-22), and inclusion of untrusted remote content (CWE-829), from running the generator on an attacker-controlled or attacker-influenced OpenAPI description. No code execution. Notable because Kiota is otherwise the hardened generator (it resists the code-injection class).

The relevant threat is not "change the generated output" (an attacker who fully controls the description can already do that) but the side effects on the build host: outbound requests from inside the CI network (cloud metadata, internal-only services) and reads of local files the attacker never possessed, whose contents are then inlined into the generated — and typically committed/published — client. It also bypasses controls that review the description document but not externally-referenced content.

Patches

Fixed in 1.29.1 and 1.32.5 (https://github.com/microsoft/kiota/pull/7888). External reference resolution is now default-deny: a new AllowedExternalOriginsStreamLoader refuses to load any external $ref — remote http(s) URLs and local file paths alike — unless its origin/path is explicitly allow-listed. A new --allowed-external-origins parameter (added to the commands that load OpenAPI descriptions) opts specific origins back in, accepting *, full URIs, URI patterns, full paths, relative paths, or path patterns (wildcards supported). With no allow-list entries, external references are not loaded at all.

Remediation

Upgrade to Kiota 1.29.1, 1.32.5, or later. External references now require explicit opt-in via --allowed-external-origins; add only trusted origins/paths.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2026-59867

CVE-2026-59867:

7.1

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

SSVC / BOD 26-04 ↗

Exploitation NoneAutomatable NoTech Impact Partial

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Package Name	Ecosystem	Vulnerable Versions	First Patched Version
Microsoft.OpenApi.Kiota	nuget	>= 1.30.0, < 1.32.5	1.32.5
Microsoft.OpenApi.Kiota.Builder	nuget	>= 1.30.0, < 1.32.5	1.32.5

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability exists in the way Microsoft Kiota handles external references ($ref) in OpenAPI documents during code generation. Kiota utilized the Microsoft.OpenApi.Reader library, which by default resolves and fetches any external reference, whether it's a remote URL or a local file path. This behavior was exposed through the Kiota.Builder.OpenApiDocumentDownloadService.CreateOpenApiDocumentAsync function, which configured the OpenAPI reader to load external references without any security restrictions. Consequently, an attacker could craft an OpenAPI document with a malicious $ref to trigger a Server-Side Request Forgery (SSRF) or a Local File Inclusion (LFI) on the machine running the kiota generate command.

The patch addresses this by introducing a new AllowedExternalOriginsStreamLoader which acts as a security control. This new loader is now used by default and it validates any external reference against a user-provided allow-list of origins. The DefaultStreamLoader.LoadAsync function, which performs the actual fetching, is now only called for allowed origins. Therefore, the root cause was the unrestricted use of the DefaultStreamLoader's capabilities, which was fixed by wrapping it with a security-conscious loader.

Vulnerable functions

Kiota.Builder.OpenApiDocumentDownloadService.CreateOpenApiDocumentAsync

src/Kiota.Builder/OpenApiDocumentDownloadService.cs

This function is responsible for configuring the OpenAPI reader. Before the patch, it configured the reader to use the default stream loader which insecurely loaded external references from URLs and local files, leading to SSRF and LFI. The patch introduces a custom stream loader that validates external origins against an allow-list.

Microsoft.OpenApi.Reader.DefaultStreamLoader.LoadAsync