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

## Summary Microsoft Kiota resolved OpenAPI `$ref`s by fetching remote `http(s)` URLs and reading local files (including absolute / out-of-tree paths), inlining the referenced schema into the generated client. Running `kiota generate` on a spec whose `$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.

Source published

24 Jul 2026 16:10:17 UTC

Source modified

17 Aug 2026 15:00:08 UTC

Observed here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N

Publisher rating · HIGH