CVE-2026-59859 — Vulnerability in Microsoft.OpenApi.Kiota — CVE...

# Impact The Kiota PHP code generator is vulnerable to a code generation literal injection attack. The generator embeds string values from OpenAPI fields (e.g. `description`, default values, and property names) directly into PHP double-quoted string literals without properly escaping the `$` character. Since PHP evaluates string interpolation expressions like `"${expr}"`, `"$var"`, and `"{$obj->prop}"` within double-quoted strings at runtime, an attacker who controls an OpenAPI specification file can inject arbitrary PHP code into generated model and request-builder classes. # Who is impacted Developers using Kiota to generate PHP API clients from external or untrusted OpenAPI specifications Teams with CI/CD pipelines configured to automatically regenerate client code from remote specs Applications that deploy generated PHP code to production servers # Vulnerability details Affected component: `StringExtensions.cs` Root cause: The shared `SanitizeDoubleQuote()` function in `Writers/StringExtensions.cs` does not escape the `$` character. As a result, any schema-derived string emitted as a PHP double-quoted literal preserves `$`-prefixed interpolation constructs (`${...}`, `$var`, `{$...}`) verbatim, which PHP evaluates at runtime instead of treating as literal text. This is the same class of code-generation literal-injection flaw previously fixed for the Ruby generator (`#` interpolation), recurring here as a missed variant for PHP's `$` interpolation in the sibling sanitizer helper. # Attack vectors OpenAPI `description` and default fields in schema properties Property wire-name keys embedded in deserializer/serializer methods Any schema-derived string embedded in PHP double-quoted literals Severity: Critical when generated code reaches production; High for CI/CD environments with access to production secrets; Medium for public third-party specs; Low for developer-controlled specs. # Patches [#7863](https://github.com/microsoft/kiota/pull/7863) # Workarounds If you cannot upgrade immediately: 1. Audit and sanitize OpenAPI specifications: Review all OpenAPI specification files for any descriptions, default values, or property names containing the `$` character. Remove or replace any suspicious strings before code generation. 2. Code review of generated files: Implement mandatory code review of all generated PHP files before merging into any branch. Look for double-quoted strings containing `${`, `$var`, or `{$` patterns. 3. Restrict specification sources: Only consume OpenAPI specifications from trusted internal sources. Avoid automatic code generation from external or third-party APIs until this patch is applied. 4. Isolate generated code from production: Do not deploy generated PHP models to production environments unless the specification source has been verified and reviewed. 5. Manual escaping (temporary): If regeneration is not possible, manually inspect and edit generated files to escape any `$` characters in double-quoted string literals (replace `$` with `\$`). # Remediation Upgrade Kiota to 1.29.1, 1.32.4, or later. Regenerate/refresh existing generated clients as a precaution: Refreshing generated clients ensures previously generated vulnerable code is replaced with hardened output.