CVE-2026-73851

Kiota is an OpenAPI based HTTP Client code generator. Prior to 1.29.1 and 1.34.0, an attacker who controls or tampers with the OpenAPI description consumed by Kiota can supply a file reference that resolves outside the manifest package (e.g. ../../../../etc/passwd, an absolute path, or a file:// / http(s):// URI). When the generated manifest is deployed and consumed by an AI host, this can lead to inclusion or disclosure of files outside the intended package boundary. This vulnerability is fixed in 1.29.1 and 1.34.0.

Kiota is an OpenAPI based HTTP Client code generator. Prior to 1.29.1 and 1.34.0, an attacker who controls or tampers with the OpenAPI description consumed by Kiota can supply a file reference that resolves outside the manifest package (e.g. ../../../../etc/passwd, an absolute path, or a file:// / http(s):// URI). When the generated manifest is deployed and consumed by an AI host, this can lead to inclusion or disclosure of files outside the intended package boundary. This vulnerability is fixed in 1.29.1 and 1.34.0.

Impact

Kiota generates AI plugin manifests from an OpenAPI description. When the description contains an x-ai-capabilities response semantics static_template (or the adaptive-card extension x-ai-adaptive-card), the file reference is written into the generated manifest's response_semantics.static_template.file and is later resolved by the AI host relative to the plugin package.

An attacker who controls or tampers with the OpenAPI description consumed by Kiota can supply a file reference that resolves outside the manifest package (e.g. ../../../../etc/passwd, an absolute path, or a file:// / http(s):// URI). When the generated manifest is deployed and consumed by an AI host, this can lead to inclusion or disclosure of files outside the intended package boundary (CWE-22 Path Traversal, CWE-829 Inclusion of Functionality from an Untrusted Control Sphere).

A mitigation shipped in v1.32.5 (ExtensionResponseSemanticsStaticTemplate.IsSafeFileReference) rejected literal traversal, rooted paths, drive-qualified paths, and absolute URIs. However, that check inspected the raw reference string, so percent-encoded payloads bypassed every check and were still emitted verbatim. Examples that were incorrectly accepted as safe:

| Input | Decodes to | |-------|-----------| | %2e%2e/card.json | ../card.json | | ..%2f..%2f..%2f..%2f..%2f..%2fetc%2fpasswd | ../../../../../../etc/passwd | | file%3A%2F%2F%2Fetc%2Fpasswd | file:///etc/passwd | | %2e%2e%2f%2e%2e%2f%2e%2e%2fetc%2fpasswd | ../../../etc/passwd |

Multi-level (double) encoding such as %252e%252e%252fcard.json was also affected. A follow-up review found additional residual bypasses of the same validator: an embedded NUL byte (%00) that truncated the path and defeated the parent-directory segment check, encoding nested deeper than the decode budget (which failed open), and Unicode full-width homoglyphs (e.g. %EF%BC%8E%EF%BC%8E → ．．).

Patches

• The percent-encoding bypass is fixed by decoding the reference (bounded multi-pass) before validation: https://github.com/microsoft/kiota/pull/7910
• Residual bypasses (NUL / control characters, decode-budget fail-open, Unicode homoglyphs) are fixed by failing closed on residual encoding, rejecting control characters, and NFKC-folding before validation: https://github.com/microsoft/kiota/pull/7913 (tracking issue https://github.com/microsoft/kiota/issues/7912)

Users should upgrade to the first released Microsoft.OpenApi.Kiota version that includes these fixes (the release following 1.33.0).

Workarounds

• Only generate clients/plugins from trusted OpenAPI descriptions.
• Review generated plugin manifests before deployment and reject any response_semantics.static_template.file value that is not a simple relative path within the adaptiveCards/ package folder (no .., no rooted/absolute paths, no URIs, no percent-encoded separators).

References

• CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
• CWE-829: Inclusion of Functionality from an Untrusted Control Sphere
• Affected code: src/Kiota.Builder/OpenApiExtensions/OpenApiAiCapabilitiesExtension.cs (IsSafeFileReference) and enforcement in src/Kiota.Builder/Plugins/PluginsGenerationService.cs.

Kiota is an OpenAPI based HTTP Client code generator. Prior to 1.29.1 and 1.34.0, an attacker who controls or tampers with the OpenAPI description consumed by Kiota can supply a file reference that resolves outside the manifest package (e.g. ../../../../etc/passwd, an absolute path, or a file:// / http(s):// URI). When the generated manifest is deployed and consumed by an AI host, this can lead to inclusion or disclosure of files outside the intended package boundary. This vulnerability is fixed in 1.29.1 and 1.34.0.

Kiota is an OpenAPI based HTTP Client code generator. Prior to 1.29.1 and 1.34.0, an attacker who controls or tampers with the OpenAPI description consumed by Kiota can supply a file reference that resolves outside the manifest package (e.g. ../../../../etc/passwd, an absolute path, or a file:// / http(s):// URI). When the generated manifest is deployed and consumed by an AI host, this can lead to inclusion or disclosure of files outside the intended package boundary. This vulnerability is fixed in 1.29.1 and 1.34.0.

Impact

Kiota generates AI plugin manifests from an OpenAPI description. When the description contains an x-ai-capabilities response semantics static_template (or the adaptive-card extension x-ai-adaptive-card), the file reference is written into the generated manifest's response_semantics.static_template.file and is later resolved by the AI host relative to the plugin package.

An attacker who controls or tampers with the OpenAPI description consumed by Kiota can supply a file reference that resolves outside the manifest package (e.g. ../../../../etc/passwd, an absolute path, or a file:// / http(s):// URI). When the generated manifest is deployed and consumed by an AI host, this can lead to inclusion or disclosure of files outside the intended package boundary (CWE-22 Path Traversal, CWE-829 Inclusion of Functionality from an Untrusted Control Sphere).

A mitigation shipped in v1.32.5 (ExtensionResponseSemanticsStaticTemplate.IsSafeFileReference) rejected literal traversal, rooted paths, drive-qualified paths, and absolute URIs. However, that check inspected the raw reference string, so percent-encoded payloads bypassed every check and were still emitted verbatim. Examples that were incorrectly accepted as safe:

| Input | Decodes to | |-------|-----------| | %2e%2e/card.json | ../card.json | | ..%2f..%2f..%2f..%2f..%2f..%2fetc%2fpasswd | ../../../../../../etc/passwd | | file%3A%2F%2F%2Fetc%2Fpasswd | file:///etc/passwd | | %2e%2e%2f%2e%2e%2f%2e%2e%2fetc%2fpasswd | ../../../etc/passwd |

Multi-level (double) encoding such as %252e%252e%252fcard.json was also affected. A follow-up review found additional residual bypasses of the same validator: an embedded NUL byte (%00) that truncated the path and defeated the parent-directory segment check, encoding nested deeper than the decode budget (which failed open), and Unicode full-width homoglyphs (e.g. %EF%BC%8E%EF%BC%8E → ．．).

Patches

• The percent-encoding bypass is fixed by decoding the reference (bounded multi-pass) before validation: https://github.com/microsoft/kiota/pull/7910
• Residual bypasses (NUL / control characters, decode-budget fail-open, Unicode homoglyphs) are fixed by failing closed on residual encoding, rejecting control characters, and NFKC-folding before validation: https://github.com/microsoft/kiota/pull/7913 (tracking issue https://github.com/microsoft/kiota/issues/7912)

Users should upgrade to the first released Microsoft.OpenApi.Kiota version that includes these fixes (the release following 1.33.0).

Workarounds

• Only generate clients/plugins from trusted OpenAPI descriptions.
• Review generated plugin manifests before deployment and reject any response_semantics.static_template.file value that is not a simple relative path within the adaptiveCards/ package folder (no .., no rooted/absolute paths, no URIs, no percent-encoded separators).

References

• CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
• CWE-829: Inclusion of Functionality from an Untrusted Control Sphere
• Affected code: src/Kiota.Builder/OpenApiExtensions/OpenApiAiCapabilitiesExtension.cs (IsSafeFileReference) and enforcement in src/Kiota.Builder/Plugins/PluginsGenerationService.cs.