Microsoft Kiota: Arbitrary file write + code-injection via x-ms-kiota-info clientClassName and clientNamespaceName
Summary
Microsoft Kiota emitted the x-ms-kiota-info extension's clientClassName or clientNamespaceName value
raw, with no identifier or path sanitization, as both the generated client's class/namespace name
and part of the generated output path. When kiota generate is run without -c/--class-name — the
zero-config workflow that x-ms-kiota-info is explicitly designed for (the API provider supplies the names in
the description so consumers don't have to) — an attacker who controls or tampers with the OpenAPI description
could therefore:
- (CWE-22) write the generated source file to a path outside the
-o output directory — e.g.
clientClassName: "/var/www/html/shell"; and
- (CWE-94) inject arbitrary text into the generated class/namespace declaration, corrupting the generated
client.
Confirmed on Kiota 1.32.4 (the self-contained linux-x64 release binary), i.e. after the earlier
writer-sink hardening — that fix escaped property/enum/default/serialization sinks but never sanitized the
provider-supplied clientClassName / clientNamespaceName.
Details
clientClassName reached two unsanitized sinks (observed in the generated C#; the same raw emission occurred
for Java, Go, TypeScript, Python, and PHP):
```
# output FILENAME (CWE-22): clientClassName flows into the file path
clientClassName: "/abs/path/PWNED" -> /abs/path/PWNED.cs (written outside -o)
# class declaration (CWE-94): clientClassName flows verbatim into the type declaration
clientClassName: 'Pwn { } public class INJECTED { } public partial class RealClient'
-> public partial class Pwn { } public class INJECTED { } public partial class RealClient : ... { }
```
clientNamespaceName reached the analogous namespace/path sinks.
Impact
A developer or CI host generating a client from an attacker-controlled or compromised OpenAPI description
(without -c) could create/overwrite a generated source file at an attacker-influenced path and emit
attacker-controlled text into the generated client.
This does not reach clean remote code execution: because clientClassName is reused verbatim at multiple
sites (the class name and the constructor name), injected code cannot be made to compile — it breaks the
build. So the code-injection vector is a generation/build-corruption (integrity/DoS), and the high-severity
primitive is the file write. CWE-22 / CWE-94.
Patches
Fixed in 1.32.5 (https://github.com/microsoft/kiota/pull/7884). clientClassName and
clientNamespaceName sourced from x-ms-kiota-info are now sanitized before use:
GenerationConfiguration.SanitizeClientClassName strips any character outside [A-Za-z0-9_] and any invalid
leading character (falling back to ApiClient), and SanitizeClientNamespaceName restricts to
[A-Za-z0-9._-], collapses consecutive dots, strips invalid leading characters (falling back to ApiSdk).
This removes path separators, drive/colon, .., quotes, and braces, so the values can no longer influence
the output path or inject into the declaration.
Remediation
Upgrade to Kiota 1.32.5 or later and regenerate affected clients.
